Chapter 4, Section 3Conservation of Energy

The Law of Conservation of Energy

Conservation of Energy

• The law of conservation of energy states that energy cannot be created or destroyed.

• Energy can only be converted from one form to another, or transferred from one place to another.

4.3

Roller Coaster

Energy Transformation on a Roller Coaster

• You have experienced many situations that involve conversions between potential and kinetic energy.

Conversions Between Kinetic and Potential Energy

Conservation of Energy

• To understand the energy conversions that occur, it is helpful to identify the mechanical energy of a system.

4.3

Conversions Between Kinetic and Potential Energy

Conservation of Energy

• Mechanical energy is the sum of the gravitational or elastic potential energy and kinetic energy in a system of objects.

4.3

• Energy transformations occur during projectile motion when an object moves in a curved path.

Energy Transformations in Projectile Motion

Conservation of Energy4.3

Energy Transformations in Projectile Motion

Conservation of Energy

• However, the mechanical energy of the ball remains constant as it rises and falls.

4.3

• Energy can change from one form to another, but the total amount of energy never changes.

The Law of Conservation of EnergyConservation of Energy

4.3

Thermal Energy

Thermal energy is the energy of heat or hot objects.

• While coasting along a flat road on a bicycle, you know that you will eventually stop if you don’t pedal.

Is energy always conserved?Conservation of Energy

• If energy is conserved, why wouldn’t your kinetic energy stay constant so that you would coast forever?

4.3

In this case, some of the mechanical energy was converted to thermal energy, or heat, because of the friction of the tires on the road.

Sometimes mechanical energy is not conserved.

If any losses of mechanical energy occur, however, total energy is still conserved. It is a law that is never broken!

In this case, some of the mechanical energywas converted to thermal energy, or heat, because of the friction of the tires on the road.

Sometimes mechanical energy is not conserved.

If any losses of mechanical energy occur, however, total energy is always conserved. It is a law that is never broken!

Power

__________ is the rate at which __________ is converted, or used.

Power and energy are related, but they are not the same thing!

4.3