432 Unit 3: Motion and Forces
KEY CONCEPTS
1. Explain the relationship
between work and energy.
2. How are potential energy and
kinetic energy related to
mechanical energy?
3. When one form of energy
changes into one or more
other forms of energy, what
happens to the total amount
of energy?
CRITICAL THINKING
4. Infer Debra used 250 J of
energy to roll a bowling ball.
When the ball arrived at the
end of the lane, it had only
200 J of energy. What hap-
pened to the other 50 J?
5. Calculate A satellite falling to
Earth has a kinetic energy of
182.2 billion J and a potential
energy of 1.6 billion J. What is
its mechanical energy?
CHALLENGE
6. Apply At what point in its
motion is the kinetic energy
of the end of a pendulum
greatest? At what point is its
potential energy greatest?
When its kinetic energy is half
its greatest value, how much
potential energy did it gain?
Forms of Energy
As you have seen, mechanical energy is a combination of kinetic
energy and potential energy. Other common forms of energy are
discussed below. Each of these forms of energy is also a combination
of kinetic energy and potential energy. Chemical energy, for example,
is potential energy when it is stored in bonds.
Thermal energy is the energy an object has due to the motion of its
molecules. The faster the molecules in an object move, the more
thermal energy the object has.
Chemical energy is the energy stored in chemical bonds that hold
chemical compounds together. If a molecule’s bonds are broken or
rearranged, energy is released or absorbed. Chemical energy is used to
light up fireworks displays. It is also stored in food and in matches.
Nuclear energy is the potential energy stored in the nucleus of an
atom. In a nuclear reaction, a tiny portion of an atom’s mass is turned
into energy. The source of the Sun’s energy is nuclear energy. Nuclear
energy can be used to run power plants that provide electricity.
Electromagnetic energy is the energy associated with electrical
and magnetic interactions. Energy that is transferred by electric
charges or current is often called electrical energy. Another type of
electromagnetic energy is radiant energy, the energy carried by light,
infrared waves, and x-rays.
It is possible to transfer, or convert, one energy form into one or more
other forms. For example, when you rub your hands together on a
cold day, you convert mechanical energy to thermal energy. Your body
converts chemical energy stored in food to thermal and mechanical
energy (muscle movement).
MAIN IDEA WEB
Include common forms of
energy in your web.
