WHAT IS VOLTAGE?

Of several electricity concepts, the idea of "voltage" or "electrical potential" is probably the hardest to understand.

It's also really tough to explain. It's a headache for both the student and the teacher. To understand voltage, it helps if you first understand a little about its nearest relative, magnetism.

Most of us are familiar with magnetic fields. Small magnets are surrounded with an invisible "field" which pulls upon iron, and which can attract or repel other magnets. The magnetic field forces oblong magnetic objects (such as iron rods, or iron powder) to twist and align to follow particular directions. Put a bar magnet under a piece of paper, sprinkle on some iron filings, and the filings all line up and show the general shape of the invisible field. Obtain a small compass, and you'll see the little compass pointer twist and align with the magnetic field of the earth. That's magnetism.

There is another type of invisible field besides magnetism. It is called the "electric field" or "electrostatic field" or "e-field." This second kind of field is much like magnetism. It's invisible, it has lines of flux, and it can attract and repel objects. However, it is not magnetism, it is something separate. It is voltage.

Most people know about magnetic fields but not about e-fields or "voltage fields." In part, this is because magnetism is explained in school, but for some reason voltage fields are hidden away under the name "static electricity." E-fields are never mentioned in beginner's science textbooks. This is odd, since voltage and "static electricity" go together. Whenever a negative charge attracts a positive charge, invisible fields of voltage MUST EXIST between the charges. Voltage causes the attraction between opposite charges; the voltage fields reach across space. In reality, "static" electricity has nothing to do with motion (or with being static.) Instead static electricity involves high voltage. Scuff across a rug, and you charge your body to several thousand volts. When you remove a wool sock from your clothes dryer, and all the fibers stand outwards, the fibers are following the invisible lines of voltage in the air. Fibers are the "iron filings" that make the voltage patterns visible. And whenever the charges within a conductor are forced to flow, they only move because they're being driven along by a voltage-field which runs through the length of the wire. Voltage causes current. Voltage causes dryer-cling, but it also causes electric currents in wires. Another way to say it: electric currents are caused by "static electricity," and "static electricity" is not necessarily static. The connection between voltage and "static" electricity is not explained in the books, and that's one main reason why voltage seems so complicated and mysterious.

The Simple Math Behind "Voltage"

To be a bit more specific, Voltage is a way of using numbers to describe an electric field. Electric fields or "E-fields" are measured in volts over a distance; volts per centimeter for example. A stronger e-field has more volts per centimeter than a weaker field. Voltage and e-fields are basically the same thing: if e-fields are like the slope of a mountainside, then the volts are like the various heights of each different spot on the mountain. The slope of a mountainside can make a boulder start rolling. So can the differing heights of the different points on the mountain, it's just another way to describe the same thing. "Voltage" and "e-fields" are two ways to describe the same basic concept.

When you have e-fields, you have voltage. E-fields can exist in the air, and so can voltage. Whenever you have a high voltage across a short distance, then you have strong e-fields. Whenever an e-field is attracting or repelling an object, instead we could say that the object is being driven by the voltage in the space around the object.

How High is my Voltage?

Can an object have a certain voltage? No. Why not?

Well, please tell what my distance is. What is my distance? That's a ridiculous question, because I didn't tell you my distance FROM WHAT. Voltage is a bit like length; it is a measurement made BETWEEN two things. My distance is 300ft above sea level, but simultaneously my distance is also 1cm from the floor (since I'm not barefoot,) and it's also 93 million miles from the sun. My voltage might be -250 Volts in relation to the earth, but it also might be billions of volts when compared to the moon. Volts are always measured along the flux lines of electric field, therefore voltage is always measured between two charged objects. If I start at the negative end of my flashlight battery, I can call that end "zero volts", and so the other end must be positive 1.5 volts. However, if I start at the POSITIVE end instead, then the positive battery terminal is zero volts, and the other terminal is negative 1.5 volts. Or, if I start half way between the battery terminals, then one terminal is -.75 volts, and the other terminal is +.75 volts. OK, what is the REAL voltage of the positive battery terminal? Is it actually zero, or actually +1.5, or is it +.75 volts? Nobody can say. The terminal can have several voltages at the same time. But this is no big deal, because neither can anyone tell you the battery's distance! We can easily imagine the distance between two points, and we can also imagine the voltage between two points. But single objects don't "have distance", and single objects also don't "have voltage."

Un-twisting the Terminology

You've probably heard of electromagnetic fields and electromagnetism. In the word "Electromagnetism," the term "electro" does not refer to electricity. Instead it refers... to voltage! Electromagnetism is the study of e-fields and magnetic fields: electro/magnetism. Charge flow (electric current) is intimately associated with magnetism, and separated opposite charges are intimately associated with voltage. A flow of electromagnetic energy along a cable is composed half of electric current, and half of voltage. It is "voltagecurrent," it is electrostatic/magnetostatic, it's electro-magnetism. Electromagnetism is a two-sided coin, so what is voltage? It's one side of EM (the other side being magnetism.)

Besides not being found in elementary school science books, Voltage is also missing from our everyday language. If we have no common words to describe something, we tend to never talk about it. We have trouble even thinking about it, or believing it exists. For example, we have the word "magnetism", and most people have heard of magnetic fields. ELECTRIC fields exist too, but unfortunately "electri-cism" is not an English word. Everyone can discuss magnetism, but nobody ever talks about "electricism." Without the word "electricism," we have a tough time talking about electric fields, or about electric attraction/repulsion forces, and we never realize that they are important in electric circuits. Yet there's a word we could use instead of "Electricizm." We don't have to coin some weird new term.

If magnetism is "that which involves magnetic fields", then what is "that which involves electric fields?"

Voltage!

Pick up some nails with a magnet, and that's an example of magnetism, then pick up some bits of paper with a fur-rubbed balloon, and that's an example of voltage. What are the three kinds of invisible field? Gravity, magnetism... and voltage!

Perhaps we should change the word "Electromagnetism" into "Voltagemagnetism?" (grin!)

VOLTAGE SURROUNDS TWO ELECTRIC CHARGES

MAGNETISM SURROUNDS A MAGNET'S POLES

Electromagnetic Duality

Voltage and magnetism form a pair of twins; they are two halves of a duality. Physicists and engineers even use the word "dual" to describe them: voltage is the "dual" of magnetism, and magnetism is the "dual" of voltage. This duality raises its head in many places in the physical sciences. One small analogy: A spinning flywheel can store energy. So can a compressed spring. In electrical physics, a superconductor ring can store energy in the form of magnetism, and a capacitor can store energy in the form of voltage. A coil of wire and a capacitor are the "duals" of each other, since one involves magnetism, and the other is based on voltage.

Voltage Energy

Voltage is intimately connected with electrical energy. So is magnetism. We can even say that electrical energy is the fundamental object of our study, while voltage and magnetism are the two faces it displays to the outside world. Another analogy: in mechanical physics, both the Kinetic energy (KE) and the Potential energy (PE) are part of matter: relative motion of an object has Kinetic Energy, and stretched or compressed objects (e.g. springs or rubber bands) have Potential Energy. In a similar way, electrical kinetic energy appears whenever positive charges flow through negative charges. We call this "electric current," and it causes magnetism. On the other hand, electrical potential energy appears whenever positive charges are yanked away to a distance from their corresponding negative charges. We call this "net electrostatic charge," and it causes voltage. Electrical KE is associated with current, and electrical PE is associated with voltage. If electrical energy is the same as Electromagnetism, then maybe we should be more sensible and name it "VoltageCurrent-ism."

Potential Energy vs. "Potential"

Voltage is also called "electrical potential."

So... is voltage a type of potential energy? Close, but not totally accurate. Confusion between voltage and potential energy is a common mistake. Think of it like this. If you roll a big boulder to the top of a hill, you have stored some potential energy. But after the boulder has rolled back down, THE HILL IS STILL THERE. The hill is like voltage: the height of the hill has "Gravitational Potential." But the hill is not *made* of Potential Energy, since we need both the hill *and* the boulder before we can create potential energy. The situation with voltage is similar. Before we can store any ELECTRICAL potential energy, we need some charges, but we also need some voltage-field through which to push our charges. The charges are like the boulder, while the voltage is like the hill (volts are like height in feet. Well, sort of...) But we wouldn't say that the Potential Energy is the boulder, or we wouldn't say the hill is the PE. In the same way, we should not say that electric charges are Potential Energy, neither should we say that voltage is Potential Energy. However, there is a close connection between them. Voltage is "electric potential" in approximately the same way that the height of a hill is connected with "gravitational potential." You can push an electron up a voltage-hill, and if you let it go it will race back down again.

Currents don't have Voltage

Voltage is not a characteristic of electric current. It's a common mistake to believe that a current "has a voltage" (and this mistake is probably associated with the 'current electricity' misconception, where people believe that 'current' is a kind of substance that flows). Voltage and current are two independent things. It is easy to create a current which lacks a voltage: just short out an electromagnet coil. It is also easy to create a voltage without a current: flashlight batteries maintain their voltage even when they are sitting on the shelf in the store. Water analogy: Think of water pressure without a flow. That's like voltage alone. Now think of water that's coasting along; a water flow without a pressure. That's like electric current alone.

"Kinds" of Electricity?

Grade-school textbooks wrongly teach that electricity comes in two types: static electricity and current electricity. These textbooks would be much closer to the truth if they instead said this:

The two halves of "electricity" are "voltage electricity" and "current electricity."

Still misleading, since the meaning of the word "electricity" is not clearly defined. It would be better if they said that electrical energy has two main characteristics: voltage and current. But the above statement is not nearly as bad as the stuff they teach about "static vs. current."

For one thing, the static stillness of the charges is not important. For example, if we view a frozen "snapshot" of an electrical phenomenon, we'd be seeing an electrostatic situation. "Static" electricity is NOT electricity which is static. Instead, "static charge" really means "separated opposite charges". We should not be surprised to learn that "static electricity" is able to flow from place to place without losing any of its characteristics. Maybe it's not "static" anymore, but it's still Static Electricity. The lack of motion doesn't matter, since a separation of charge can move along. It's the IMBALANCE between opposite charges that's important, and their "static-ness" is not.

NOTE: Do you see how K-6 textbook authors could be playing a game of 'telephone?' In this game, words are progressively distorted by errors in communication. In K-6 textbooks the science concepts become more and more distorted over the years. Authors are taught from earlier textbooks, and often they get their information directly from modern textbooks. Then they write new ones. If authors make mistakes, what will happen? Start out by saying "electromagnetism has two complimentary halves, voltage and current". Decades later we end up with books which are teaching kids something like this: "the two forms of electricity are static electricity and current electricity." Wrong. Yet we can see where the crazy stuff originally came from.

Seeing the Invisible Voltage

Magnetic fields are invisible, and so is voltage. Both can be made visible. Iron filings let us see magnetic fields. To see voltage, suspend some metal or plastic fibers in oil, or sprinkle grass seeds on a pool of glycerine. If we then expose the oil to the strong voltage-field surrounding a charged object, the fibers or grass seeds will line up and show the shape of the field. Rub a balloon on your head, hold it near the suspended fibers, and you'll "see" the lines of e-field flux.

Measuring Voltage

To measure current, we allow the magnetism around a coil of wire to deflect a compass needle. To measure voltage, we allow the "electricism" between a pair of delicately suspended metal plates to deflect one of those plates. The simplest voltmeter is called a "foil-leaf electroscope." Electroscopes are simple versions of zero-current voltmeters. find such things in books about "static electricity", when they really should be in all electronics books. A more complicated version of the foil-leaf electroscope is called a "quadrant electrometer." These two devices can measure voltage directly, without creating any electric current at all. Besides the moving capacitor plates, there are a few other ways to measure voltage too.

The Voltage of Light

Here's a strange idea: Flowing Electromagnetic energy always has voltage. For example, if you touch the antenna of a powerful radio transmitter, you can receive an electric shock because of the high voltage at the antenna. Radio waves are electromagnetism, and the intense waves surrounding a radio transmitter's antenna will have a high voltage-field. Radio waves can be measured in terms of voltage. Even the brightness of the light from the sun can be measured in terms of volts per meter. So can the energy which comes from the electric generators and flows along wires to a 120v table lamp. All of these involve electric fields (and voltage), and magnetic fields (and current.) Power lines deal with voltage, but in the same way, so do light beams and optical fibers.

Expose All Students to High Voltage! :)

"High voltage." Might you already know what that is? It's not just the dangerous devices behind the electric company fence. High voltage is also balloons rubbed upon your hair, and "static electric generators" and their very long sparks. You might be interested to know that ALL voltage create the same effects as "High Voltage." The effects are just weaker. Understand "high voltage," and you'll understand voltage itself. High voltage devices are not just toys, they are educational: they let us experience voltage directly. If you want to understand magnetism, then play with electromagnet coils and strong magnets. If you want to understand voltage, then get yourself a VandeGraaff generator.

Voltage has wrongly been hidden within "static electricity" and declared to be an obsolete and useless science, important only for historical reasons. But in a certain sense, "static electricity" *IS* voltage. Static electricity is a high-voltage phenomena. If we stop teaching about "static electricity," and regard it as ancient and useless "Ben-Franklinish" stuff, then we also stop teaching about voltage. Can you see why voltage has become such a mystery? We've nearly eliminated "static electricity" from high school science classes, and so we've also throw away our basic voltage concepts.

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MISC. NOTES

Imagine a waterwheel being turned by a stream of water pouring from above. If the water is like the flowing electric charge, and the waterwheel is like an electric motor, then what is voltage? Voltage is like the height of the stream above the wheel, or like its slope from the top of the wheel to the pool below. Without a height difference, there can be no water current and no work done by the waterwheel. Without a voltage difference across an electric motor, there can be no electric current and no work done by the motor.

voltage is like an electrical pressure or push, it can cause electric charges to flow. Or, if flowing charge is suddenly blocked, this can cause a voltage to appear. But current can exist without voltage, and voltage can exist without current.

voltage exists in space, not just on surfaces. Rub an inflated balloon on your arm hairs, then wave the balloon around so it makes the hairs stand up. You are seeing and feeling voltage in the space between the balloon and your arm. Think about a 9v battery. The 9 volts aren't on the surface of the battery terminal, they are in the space between the terminals, like the magnetic field between a north and a south pole. A 9v battery is like an "electret", the electric version of a bar magnet.

An inductor (an electromagnet coil) is an electric current device. A capacitor is an electric voltage device. If energy is stored in a shorted coil, the energy is in the surrounding magnetic field, and there must be an electric current circulating in the coil. If energy is stored in a non-shorted capacitor, the energy is in the voltage field between the plates. If the short is suddenly removed from the inductor, there is a loud bang, and a huge voltage briefly appears. If a short is suddenly connected to a capacitor, there is a loud bang and a huge current briefly appears. Capacitor, coil. Electro, magnetism. "EM" energy.

voltage is the stuff that connects the protons and electrons of atoms to each other, and it connects atoms together to form objects. Pull on your finger, and you are feeling the microscopic voltage between the atoms. Without voltage, there would be no solids or liquids in the universe, just gas. When you break a solid object, you are defeating the attractive microscopic voltages which were binding it's atoms together.

The bonds between atoms are often associated with a constant voltage. If one atom is positive and the other negative, then there is a voltage between them. If billions of atoms could be line up in parallel, the voltage of the atoms could be easily measured. What would happen if we could align billions of atoms in parallel? We've just re-invented the battery. A battery is a couple of metal plates immersed in liquid. At the surface of the liquid where it touches each plate, all the atoms line up in parallel, and a voltage appears between the liquid and the metal. That's what causes the voltage of any battery: the micro-thin layer of atoms at the surface of the metal plates inside the battery. Everything else in the battery is just there to provide the electrical connections and the chemical fuel supply. Ideally, a flashlight battery could be three atoms thick (a thin film of liquid sandwiched between two thin metal films,) and it would still put out 1.5 volts.

Everyday electric motors operate by magnetic forces surrounding a coil, with electric current in the windings of the coil. Let's call this sort of device by the name "current motor". Electric motors in everyday life are invariably "current motors", but "voltage motors" exist too. They operate because of voltage-forces between charged objects. The microscopic motors used in cutting-edge nanotechnology are voltage motors. The linear chemical-motors inside your muscles are voltage motors. The spinning cilia on the tail ends of bacteria are little voltage motors. The mechanical enzymes which assemble ATP molecules (the 'energy molecules' of the cell) are voltage motors. The tiny microscopic parts inside a living cell are like little robots. They all rely on voltage motors, none use magnetic motors.

Potential energy involves stretching, squeezing, pressure and forces. Voltage is associated with electric charge which has been "stretched" or "pressurized." Spin a flywheel, that's an analogy for electric current and magnetism. Stretch a rubber band, that's an analogy for voltage and charge separation.

Is magnetism like a warping of space? Then so is voltage. Voltage and magnetism can be combined to become a traveling wave of warped space. We call these waves "light," or "radio," or "electrical energy." When the Electric Utility Companies sell you some "electricity", they really are selling you pulses of "space warp" which are guided to you by a pair of copper wires. They are selling you a combination of voltage and current. When voltage and current are there, electromagnetic energy is flowing down the wires.

What Is "Electricity"?

What is electricity? This question is impossible to answer because the word "Electricity" has several contradictory meanings. These different meanings are incompatible, and the contradictions confuse everyone. If you don't understand electricity, you're not alone. Even teachers, engineers, and scientists have a hard time grasping the concept.

Obviously "electricity" cannot be several different things at the same time. Unfortunately we have defined the word Electricity in a crazy way. Because the word "electricity" lacks a distinct meaning, we can never pin down the nature of electricity. In the end we are forced to declare that there's no such stuff as "electricity" at all! Here's a quick example to illustrate the problem.

Do generators make electricity? To answer this question, consider the household light bulb. In a lamp cord the charges (electrons) sit in one place and wiggle back and forth. That's AC or alternating current. At the same time, the waves of electromagnetic field move rapidly forward. The wave energy does not wiggle, instead it races along the wires as it flows from the distant generators and into the light bulb. OK, now ask yourself this: is an electric current a flow of "electricity?" If so, then we MUST say that the "electricity" sits inside the wires and vibrates back and forth. It does not flow forward. Next, ask yourself if electricity is a form of energy. If it's energy, then "the electricity" DOESN'T wiggle back and forth within the wires, instead it's made of EM fields and it races forward at high speed. But it cannot do both! Which one is "the electricity", the wiggling electrons, or the high-speed EM field energy? The reference books give conflicting answers, so there *is* no answer.

If someone asks whether generators make electricity, it exposes a great flaw in the way we talk about "electricity". If we can repair this flaw, perhaps our explanations will finally make sense.

Below are the most common meanings of the word Electricity. Which one do you think is right? Think about it carefully. If one of these meanings is correct, all the others must be wrong! After all, no "science term" must ever have several conflicting definitions. Unfortunately dictionaries and encyclopedias have all of these contradictions. (Click the links to find out more about each one.)

1. The scientist's definition: "Electricity" means only one thing: it's the electrons and protons, the electric charge.

Examples: CURRENT OF ELECTRICITY. QUANTITY OF ELECTRICITY. COULOMBS OF ELECTRICITY.

2. The everyday definition: "Electricity" means only one thing: the electromagnetic field energy sent out by batteries and generators.

Examples: PRICE OF ELECTRICITY. KILOWATT-HOURS OF ELECTRICITY.

3. The grade-school definition: "Electricity" means only one thing: it refers to the flowing motion of electric charge.

Examples: "CURRENT" ELECTRICITY. AMPERES OF ELECTRICITY.

4. "Electricity" means only one thing: it refers to the amount of imbalance between quantities of electrons and protons.

Example: "STATIC" ELECTRICITY. DISCHARGE OF ELECTRICITY.

5. "Electricity" is nothing other than the classes of phenomena involving electric charges.

Examples: BIOELECTRICITY, PIEZOELECTRICITY, TRIBOELECTRICITY, THERMOELECTRICITY, ATMOSPHERIC ELECTRICITY ...ETC.

6. Other less common definitions:

"Electricity" refers to the flowing motion of electrical energy (electric power, Watts of electricity)

"Electricity" really means the electric potential or e-field (Volts of electricity)

"Electricity" only means the glowing nitrogen/oxygen plasma (sparks of electricity)

"Electricity" is nothing but a field of science (Basic Electricity, Advanced Electricity)

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Properties of Matter

1. Gases are not matter because most are invisible.
2. Gases do not have mass.
3. A "thick" liquid has a higher density than water.
4. Mass and volume, which both describe an "amount of matter" are the same property.
5. Air and oxygen are the same gas.
6. Helium and hot air are the same gas.
7. Expansion of matter is due to expansion of particles rather than to increased particle spacing.
8. Particles of solids have no motion.
9. Relative particle spacing among solids, liquids and gases (1:1:10) is incorrectly perceived and not generally related to the density of the states.
10. Materials can only exhibit properties of one state of matter.
11. Particles possess the same properties as the materials they compose. For example, atoms of copper are "orange and shiny", gas molecules are transparent, and solid molecules are hard.
12. Melting/freezing and boiling/condensation are often understood only in terms of water.
13. Particles are viewed as mini-versions of the substances they comprise.
14. Particles are often misrepresented in sketches. No differentiation is made between atoms and molecules.
15. Particles misrepresented and undifferentiated in concepts involving elements, compounds, mixtures, solutions and substances.
16. Frequent disregard for particle conservation and orderliness when describing changes.
17. Absence of conservation of particles during a chemical change.
18. Chemical changes perceived as additive, rather than interactive. After chemical change the original substances are perceived as remaining, even though they are altered.
19. Failure to perceive that individual substances and properties correspond to certain types of particles (i.e. formation of a new substance with new properties is seen as simple happening rather than as the result of particle rearrangement).

Magnets and Magnetism

1. All metals are attracted to a magnet.
2. All silver colored items are attracted to a magnet.
3. All magnets are made of iron.
4. Larger magnets are stronger than smaller magnets.
5. The magnetic and geographic poles of the earth are located at the same place.
6. The magnetic pole of the earth in the northern hemisphere is a north pole, and the pole in the southern hemisphere is a south pole.

Lithosphere

1. Any crystal that scratches glass is a diamond.
2. Rocks must be heavy.
3. Soil must have always been in its present form.
4. Mountains are created rapidly.
5. Earth is molten, except for its crust.
6. Earth's gravitational attraction is drastically reduced on mountaintops.
7. Continents do not move.
8. Boiling or burning radioactive material can reduce radiation.
9. All radioactivity is man-made.

Light

1. Light is associated only with either a source or its effects. Light is not considered to exist independently in space; and hence, light is not conceived of as "travelling".
2. An object is "seen" because light shines o it. Light is a necessary condition for seeing an object and the eye.
3. Lines drawn outward from a light bulb represent the "glow" surrounding the bulb.
4. A shadow is something that exists on its own. Light pushes the shadow away from the object to the wall or the ground and is thought of as a "dark " reflection of the object.
5. Light is not necessarily conserved. It may disappear or be intensified.
6. Light from a bulb only extends outward a certain distance, and then stops. How far it extends depends on the brightness of the bulb.
7. The effects of light are instantaneous. Light does not travel with a finite speed.
8. A mirror reverses everything.
9. For an observer to see the mirror image of an object, either the object must be directly in front of the mirror, or if not directly in front, then the object must be along the observer's line of sight to the mirror. The position of the observer is no t important in determining whether the mirror image can be seen.
10. An observer can see more of his image by moving further back from the mirror.
11. The mirror image of an object is located on the surface of the mirror. The image is often thought of as a picture on a flat surface.
12. The way a mirror works is as follows: The image first goes from the object to the mirror surface. Then the observer either sees the image on the mirror surface of the image reflects off the mirror and goes into the observer's eye.
13. Light reflects from a shiny surface in an arbitrary manner.
14. Light is reflected from smooth mirror surfaces but not from non-shiny surfaces.
15. Curved mirrors make everything distorted.
16. Light shines on a translucent material and illuminates it so it can be seen. Light does not travel from the translucent material to the eye.
17. Light always passes straight through a transparent material without changing direction.
18. When an object is viewed through a transparent solid or liquid material the object is seen exactly where it is located.
19. Students will often think about how a lens forms an image of a self-luminous object in the following way. They envision that a "potential image" which carries information about the object leaves the self-luminous object and travels through the space to the lens. When passing through the lens, the "potential image" is turned upside down and may be changed in size.
20. When sketching a diagram to show how a lens forms an image of an object, only those light rays are drawn which leave the object in straight parallel lines.
21. Blocking part of the lens surface would block the corresponding part of the image.
22. The purpose of the screen is to capture the image so that it can be seen. The screen is necessary for the image to be formed. Without a screen there is no image.
23. An image can be seen on the screen regardless of where the screen is placed relative to the lens. To see a larger image on the screen, the screen should be moved further back.
24. An image is always formed at the focal point of the lens.
25. The size of the image depends on the size (diameter) of the lens.
26. When a wave moves through a medium, particles of the medium move along with the wave.
27. Gamma rays, x-rays, ultraviolet light, visible light, infrared light, microwaves and radio waves are all very different entities.
28. When two pulses, travelling in opposite directions along a spring or rope meet, they bounce off each other and go back in the opposite direction.
29. Colors appearing in soap films are the same colors that appear in a rainbow.
30. Polaroid sunglasses are just dark glass or dark plastic.

Heat and Temperature

1. Heat is a substance.
2. Heat is not energy.
3. Temperature is a property of a particular material or object. (Metal is naturally cooler than plastic).
4. The temperature of an object depends on its size.
5. Heat and cold are different, rather than being opposite ends of a continuum.
6. When temperature at boiling remains constant, something is "wrong".
7. Boiling is the maximum temperature a substance can reach.
8. Ice cannot change temperature.
9. Objects of different temperature that are in contact with each other, or in contact with air at different temperature, do not necessarily move toward the same temperature.
10. Heat only travels upward.
11. Heat rises.
12. The kinetic theory does not really explain heat transfer. (It is recited but not believed).
13. Objects that readily become warm (conductors of heat) do not readily become cold.
14. The bubbles in boiling water contain "air", "oxygen" or "nothing", rather than water vapor.

Forces and Fluids

1. Objects float in water because they are lighter than water.
2. Objects sink in water because they are heavier than water.
3. Mass/volume/weight/heaviness/size/density may be perceived as equivalent.
4. Wood floats and metal sinks.
5. All objects containing air float.
6. Liquids of high viscosity are also liquids with high density.
7. Adhesion is the same as cohesion
8. Heating air only makes it hotter.
9. Pressure and force are synonymous.
10. Pressure arises from moving fluids.
11. Moving fluids contain higher pressure.
12. Liquids rise in a straw because of "suction".
13. Fluid pressure only acts downward.

Forces and Motion

1. The only "natural" motion is for an object to be at rest.
2. If an object is at rest, no forces are acting on the object.
3. A rigid solid cannot be compressed or stretched.
4. Only animate objects can exert a force. Thus, if an object is at rest on a table, no forces are acting upon it.
5. Force is a property of an object. An object has force and when it runs out of force it stops moving.
6. The motion of an object is always in the direction of the net force applied to the object.
7. Large objects exert a greater force than small objects.
8. A force is needed to keep an object moving with a constant speed.
9. Friction always hinders motion. Thus, you always want to eliminate friction.
10. Frictional forces are due to irregularities in surfaces moving past each other.
11. Rocket propulsion is due to exhaust gases pushing on something behind the rocket.
12. Time is defined in terms of its measurement.
13. The location of an object can be described by stating its distance from a given point (ignoring direction).
14. The terms distance and displacement are synonymous and may be used interchangeably. Thus the distance an object travels and its displacement are always the same.
15. Velocity is another word for speed. An object's speed and velocity are always the same.
16. Acceleration is confused with speed.
17. Acceleration always means that an object is speeding up.
18. Acceleration is always in a straight line.
19. Acceleration always occurs in the same direction as an object is moving.
20. If an object has a speed of zero (even instantaneously), it has no acceleration.

Energy

1. Energy is a thing. This is a fuzzy notion, probably because of the way that we talk about newton-meters or joules. It is difficult to imagine an amount of an abstraction.
2. The terms "energy" and "force" are interchangeable.
3. From the non-scientific point of view, "work" is synonymous with "labor". It is hard to convince someone that more work is probably being done playing football for one hour than studying an hour for a quiz.
4. An object at rest has no energy.
5. The only type of potential energy is gravitational.
6. Gravitational potential energy depends only on the height of an object.
7. Doubling the speed of a moving object doubles the kinetic energy.
8. Energy can be changed completely from one form to another (no energy losses).
9. Things "use up" energy.
10. Energy is confined to some particular origin, such as what we get from food or what the electric company sells.
11. Energy is truly lost in many energy transformations.
12. There is no relationship between matter and energy.
13. If energy is conserved, why are we running out of it?

Electricity

Positively charged objects have gained protons, rather than being deficient in electrons.

Electrons which are lost by an object are really lost (no conservation of charge).

All atoms are charged.

A charged object can only attract other charged objects.

The electrostatic force between two charged objects is independent of the distance between them.

Gravitational forces are stronger than electrostatic forces.

Batteries have electricity inside them.

Color and Vision

1. The pupil of the eye is a black object or spot on the surface of the eye.
2. The eye receives upright images.
3. The lens is the only part of the eye responsible for focusing light.
4. The lens forms and image (picture) on the retina. The brain then "looks" at this image and that is how we see.
5. The eye is the only organ for sight; the brain is only for thinking.
6. A white light source, such as an incandescent or fluorescent bulb, produces light made up of only one color.
7. Sunlight is different from other sources of light because it contains no color.
8. When white light passes through a prism, color is added to the light.
9. The rules for mixing color paints and crayons are the same as the rules for mixing colored lights.
10. The primary colors for mixing colored lights are red, blue and yellow.
11. A colored light striking an object produces a shadow behind it that is the same color as the light. For example, when red light strikes an object, a red shadow is formed.
12. The shades of gray in a black and white newspaper picture are produced by using inks with different shades of gray.
13. When white light passes through a colored filter, the filter adds color to the light.
14. The different colors appearing in colored pictures printed in magazines and newspapers are produced by using different inks with all the corresponding colors.
15. The mixing of colored paints and pigments follow the same rules as the mixing of colored lights.
16. The primary colors used by artists (red, yellow and blue) are the same as the primary colors for all color mixing.
17. Color is a property of an object, and is independent of both the illuminating light and the receiver (eye).
18. White light is colorless and clear, enabling you to see the "true" color of an object.
19. When a colored light illuminates a colored object, the color of the light mixes with the color of the object.
20. Naove explanations of visual phenomena involving color perception usually involve only the properties of the object being observed, and do not include the properties of the eye-brain system.

Biosphere

1. Coral reefs exist throughout the Gulf and North Atlantic waters.
2. Dinosaurs and cavemen lived at the same time.
3. Acquired characteristics can be inherited.
4. Winter weather can be predicted by studying the thickness of the fur of some animals.
5. Humans are responsible for the extinction of the dinosaurs.
6. Some human races have not evolved as much as others.
7. Evolution is goal-directed.
8. Evolutionary changes are driven by need.

Atmosphere

1. Rain comes from holes in clouds.
2. Rain comes from clouds sweating.
3. Rain occurs because we need it.
4. Rain falls from funnels in the clouds.
5. Rain occurs when clouds get scrambled and melt.
6. Rain occurs when clouds are shaken.
7. God and angels cause thunder and lightning.
8. Clouds move because we move.
9. Clouds come from somewhere above the sky.
10. Empty clouds are filled by the sea.
11. Clouds are formed by vapor from kettles.
12. The sun boils the sea to create water vapor.
13. Clouds are made of cotton, wool, or smoke.
14. Frontal rain is caused by "cooling by contact" between fronts.
15. The oxygen we breathe does not come from plants.
16. Gas makes things lighter.
17. One degree of temperature is smaller on the Celsius scale than on the Fahrenheit scale.
18. All rivers flow from North to South.

Astronomy

1. Stars and constellations appear in the same place in the sky every night.
2. The sun rises exactly in the east and sets exactly in the west every day.
3. The sun is always directly south at 12:00 noon.
4. The tip of a shadow always moves along an east-west line.
5. We experience seasons because of the earth's changing distance from the sun (closer in the summer, farther in the winter).
6. The earth is the center of the solar system. (The planets, sun and moon revolve around the earth.)
7. The moon can only be seen during the night.
8. The moon does not rotate on its axis as it revolves around the earth.
9. The phases of the moon are caused by shadows cast on its surface by other objects in the solar system.
10. The phases of the moon are caused by the shadow of the earth on the moon.
11. The phases of the moon are caused by the moon moving into the sun's shadow.
12. The shape of the moon always appears the same.
13. The earth is the largest object in the solar system.
14. The solar system is very crowded.
15. The solar system contains only the sun, planets and the moon.
16. Meteors are falling stars.
17. Comets and meteors are out in space and do not reach the ground.
18. The surface of the sun is without visible features.
19. All the stars in a constellation are near each other.
20. All the stars are the same distance from the earth.
21. The galaxy is very crowded.
22. Stars are evenly distributed throughout the universe.
23. All stars are the same size.
24. The brightness of a star depends only on its distance from the earth.
25. Stars are evenly distributed throughout the galaxy.
26. The constellations form patterns clearly resembling people, animals or objects.

Newton's Second Law of Motion

The acceleration produced by a particular force acting on a body is directly proportional to the magnitude of the force and inversely proportional to the mass of the body.
- Newton's Second Law of Motion, translated from the Principia's Latin

The mathematical formulation of the second law is shown to the right, with F representing the force, m representing the object's mass and a representing the object's acceleration.

Newton's Law of Gravity

Newton's law of gravity defines the attractive force between all objects that possess mass. Understanding the law of gravity, one of the fundamental forces of physics, offers profound insights into the way our universe functions.

"Mass"

Definition: Mass is the quantity of inertia possessed by an object or the proportion between force and acceleration referred to in Newton's Second Law of Motion.

This is not a very good operational definition of mass, of course. In most common instances, mass is determined by weighing the object and using the force of gravity to calculate the value automatically - which is why you can get on a scale and have read your mass.

The SI unit of mass is the kilogram (kg).

Force

Definition: Force is a quantitative description of the interaction between two physical bodies, such as an object and its environment. Force is proportional to acceleration. In calculus terms, force is the derivative of momentum with respect to time.

Contact force is defined as the force exerted when two physical objects come in direct contact with each other. Other forces, such as gravitation and electromagnetic forces, can exert themselves even across the empty vacuum of space.

The concept of force was originally defined by Sir Isaac Newton in his three laws of motion.

Force is a vector. The SI unit for force is the newton (N). One newton is equal to 1 kg * m/s².

Acceleration

Definition: Acceleration is the rate of change of velocity as a function of time. It is vector. In calculus terms, acceleration is the second derivative of position with respect to time or, alternately, the first derivative of the velocity with respect to time.

The SI units for acceleration are m / s² (meters per second squared ormeters per second per second).

About Physical Laws:

About Physical Laws:

Over the years, one thing scientists have discovered is that nature is generally more complex than we give it credit for. The following laws of physics are considered fundamental, but many of them refer to idealized, closed systems, which are hard to obtain in the real world. Also, some are altered slightly in different circumstances. Newton's laws of motion, for example, are modified by the findings of the theory of relativity, but they are still basically valid.

What are the Fields of Physics?

Physics is a diverse area of study and in order to make sense of it scientists have been forced to focus their attention on one or two smaller areas of the discipline. This allows them to become experts in that narrow field, without getting bogged down in the sheer volume of knowledge that exists regarding the natural world.

Below is a list - by no comprehensive - of different disciplines of physics. The list will be updated with new additions and definitions as appropriate.

What Is Physics?

Physics is the scientific study of matter and energy and how they interact with each other.

This energy can take the form of motion, light, electricity, radiation, gravity . . . just about anything, honestly. Physics deals with matter on scales ranging from sub-atomic particles (i.e. the particles that make up the atom and the particles that make up those particles) to stars and even entire galaxies.

Light and Vision

The irony of a chapter on Light and Vision being printed in black
and white is not lost on the author. Furthermore, as will be
discussed in the rest of this chapter, neither the perception of colour
nor accurate reproduction of colours is a straightforward topic. That
said, more than usually there will be call to visit the module website
to download additional materials, including colour illustrations.