What is Energy?

Energy

• The ability to do work or cause change.

Potential & Kinetic Energy

Potential Energy

Potential Energy

• Stored energy.• Energy of position.• The amount of usable energy in a body at

rest.• Also called gravitational potential energy.

Potential Energy

• Even though an object is not moving, it has the ability to move, if in the right position.

• Anything that can fall has the ability to create change.

Examples of Potential Energy

• By stretching a rubber band, you give it potential energy.

• A vase on a shelf has stored potential energy.

• A football being held by a quarterback has potential energy until it is thrown and it turns into kinetic energy.

Potential Energy depends on Mass and Height …

• …So, potential energy can be increased by:– Increasing Height– Increasing Mass

Kinetic Energy

Kinetic Energy

• Energy of matter in motion.• Measured by how much work is done to put

an object in motion or to rest.• The faster the object moves, the more kinetic The faster the object moves, the more kinetic

energy.energy.

Kinetic Energy depends on Mass and Speed …

• …So, kinetic energy can be increased by:– Increasing mass– Increasing speed

Examples of Kinetic Energy

• A basketball player has kinetic energy. The movements that he/she does show the energy that is being displayed while he/she is moving.

• When you are running, walking, jumping, or skiing, your body is exhibiting kinetic energy.

• Even molecules of water in a glass have kinetic energy.

Both Potential and Kinetic Energy

• A waterfall has both kinetic and potential energy.

• The water at the top of the waterfall has stored potential energy.

• Once the water leaves the top of the waterfall, the potential energy is changed into kinetic energy.

Conservation of Energy

Law of Conservation of Energy

• Energy cannot be created or destroyed; it can only be changed from one of form of energy to another form. 

• The amount of energy stays the same. 

• The ball starts with 100 J of potential energy. As the ball falls toward the ground, it gains its kinetic energy at the expense of its potential energy, so these two quantities always add up to 100 J.

• What is the potential energy and kinetic energy of the ball at the ¾ mark?

• When an object begins to move, the potential is transferred to kinetic energy.

• Ex: pendulum, roller coaster, skier, falling objects.

• Total ME (Mechanical Energy) = PE + KE

Kinetic vs. Potential

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