Potential & Kinetic Energy (Page 2 of 4) in pdf

and earth (earthquake or seismic) or water, are also examples of mechanical

kinetic energy. The amount of kinetic energy contained in a moving object

depends on its speed and its mass.

 If the motion is of electrons moving through a conductor, it is electrical kinetic

energy.

 If the motion is the random vibration of atoms and molecules, it is thermal

kinetic energy.

 Electromagnetic waves, which do not require matter to carry energy, are also

kinetic energy, because they move and can cause change or work.

 Potential energy is stored energy, not presently doing work or causing change.

 For mechanical potential energy, the energy is stored because of the object’s

position above the ground (gravitational potential energy) or the object’s

internal stress condition (elastic potential energy). Water stored behind a

high dam, which must flow downhill because of the pull of gravity, is an example

of gravitational potential energy. A stretched rubber band and compressed

spring are two examples of elastic potential energy. Deformed rock along a

fault line, which when released causes an earthquake, is another example of

elastic potential energy.

 Chemical energy and nuclear energy are both forms of potential energy,

because both store energy that is not presently doing work. In chemical energy,

it is the bonds between atoms that store the energy. In nuclear energy, it the

force that holds the atomic nucleus together that stores the energy. Only when

chemical or nuclear energy is transformed into thermal or electromagnetic

energy do they become kinetic.

 If electric charges are not moving (they are “static”), the electrical energy is

potential. A capacitor is an electrical device that directly stores electrical

charges without converting it into another form.

 Electromagnetic waves move at a very fast constant speed (the “speed of

light”), and thus can only be kinetic, not potential, energy.

 The law of conservation of energy states that energy cannot be destroyed, but

only transformed into different forms. The motion of objects can result in the

conversion of mechanical energy from potential to kinetic, sometimes in a regular

cycle. Mechanical energy is usually transformed into thermal energy by friction (a

force that opposes motion).

 In a roller coaster, potential energy is first stored in the car when it is pulled to the

top of the highest hill of the roller coaster. When the car is released and increases

its speed down the track, pulled by gravity, the potential energy is reduced as the

car moves lower, but the kinetic energy increases as the car’s speed increases.

When the car reaches the bottom of the first hill, and begins to climb the second

hill, the kinetic energy of the car is transformed back to potential energy, as the car

climbs to a higher position but slows due to the pull of gravity. Eventually the car

Potential & Kinetic Energy Page 2