Conservation of Energy

Nature possesses many recurrent themes that appear ordered and predictable. Though some people may claim otherwise, human beings appear to be more comfortable with a rational and ordered universe rather than one which is completely random.  Scientists in particular attempt to uncover these symmetries or well-defined rules, which the universe obeys.  One such symmetry is known as the law of conservation of energy.  It is a mysterious and beautiful fact about nature. Other conservation laws of nature include the conservation of momentum and electric charge.

Q: Conservation laws reflect a deep-seated human desire for order and rationality.  Does that mean that human beings invented the conservation laws?

A:  No.  Nature created these laws. We simply uncovered them and live by them.

The principal of conservation of energy implies that the amount if energy that is involved does not change, and that only its form changes.  When we throw a ball up, or when we lift a stone we transform chemical energy of food (and air) into motion or position of the ball. When we turn on a light switch, we convert electrical energy into light energy and some heat.

Conservation of energy is usually stated as the First Law of Thermodynamics which we will visit again when we discuss the laws of thermodynamics in Chapter 19. For now lets concentrate on a special case when there is no outside force applied to a mechanical system-- the total kinetic and potential energies (thus mechanical  energy) remains constant. This is called the conservation of mechanical energy, i.e.

D P.E +D K.E. = constant.

Q: Energy is generally regarded as the single most important concept in all of physics. What’s so special about energy?

A: Every interaction in our universe involves a transfer of energy or a transformation of energy from one form to another.

Q: As you walk, it is the static frictional force between your shoes and the ground that propels you. How much work is done by this force on your shoes?

A: None. At the point of contact, your shoes do not move. The ground does work on you as a whole, and you do work on your shoes.

Further Reading:

The Bishop's Color (Conservation laws in a game of chess)