# The Five Most Important Concepts in Physics

I. Energy will dissipate from an area of higher energy to one of lower energy without the input of additional energy.

This law governs all energy flow, especially observable in the cases of thermal and electrical energy flow. Heat moves from the hot tea to the relatively cold mug and surrounding air. Electrons tend to spread until an even charge is obtained throughout the entire system. This can also be directly observed with a drop of dye added to a glass of water. The color will dissipate until the entire solution is a uniform color.

II. Newton's Three Laws of Motion

1. A body in rest tends to stay at rest, and a body in motion tends to stay in motion, unless the body is compelled to change its state. The evidence supporting the first part of this statement is easily seen. We know that a wheel will not begin rolling by itself. However, we do not see the proof of the second half in our world. That is because there is an ever present inhibiting force known as friction that acts as the external force resisting perpetual motion.

2. The second law is a formula--- A=F/m. The acceleration of a body is dependent upon both the mass of the object (not its weight) and the net force perpetuating the motion (total force in the direction of the motion minus the force resisting motion). In the formula, a resisting force would be written as negative to produce a negative acceleration, which means the object would be slowing down.

3. For every action there is an equal and opposite reaction. This means that if I push you, I myself will be slightly pushed back in the process. This is the principle at work behind how jet planes and rockets propel themselves. They expell gases in the opposite direction, are pushed themselves in the process, and thus move forward.

III. The Laws of the Conservation of Energy and of Mass

These laws are intimately intertwined and state that, under normal conditions, the total energy of a contained system and the total mass of that contained system will remain contant. It also postulates that neither mass nor energy can be created or destroyed, that they merely change form (e.g. energy--- electrical changes to thermal, or mass--- liquid changes to gas). Fairly recently, though under laboratory conditions, scientists have actually observed a minute loss of total mass in a closed system, and this has been attributed to the fact that the mass had actually changed into energy. This led to a modification of the laws, which made the provision that mass and energy can actually change into each other.

IV. Wave-Particle Duality

The principle of quantum mechanics which implies that light (and, indeed, all other subatomic particles) sometimes act like a wave, and sometimes act like a particle, depending on the experiment you are performing. For instance, low frequency electromagnetic radiation tends to act more like a wave than a particle; high frequency electromagnetic radiation tends to act more like a particle than a wave.

V. The Four Fundamental Forces of Nature

Strong- This force is a nuclear force. Its purpose is to hold the nucleus of an atom together, but it decays rapidly with distance; it doesn't even extend beyond an atom's nucleus!!

Weak- The weak nuclear force is associated with beta decay. It is responsible for the nuclear breakdown of neutrons into protons and electrons.

Gravitational- The weakest of the four forces, but still holds us to the Earth, keeps our planet in orbit around the sun, and causes the tides to rise and fall.

Electromagnetic-This force is used on the atomic level to hold the atom together. It is caused by the opposing charges of electrons and protons.

 The Forces Relative Strength Range Strong 1 Short Range, about 10-14 m Electromagnetic 10-2 Infinite (1/R2) Weak 10-13 Extremely Short Range Gravitational 10-40 Infinite (1/R2)

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