Energy in Motion8SCIENCE

How is energy related to motion?• Energy of matter in motion is called kinetic energy– Energy is the ability to cause a change or do work

• Energy can be transferred between objects– Ex.: energy can be transferred through the momentum of

objects (chest bounce)

– Ex: chemical energy in a person gives muscles energy to kick a ball• energy is transferred from the leg

and foot to the ball and the ball accelerates and gains the kinetic energy

Law of Conservation of Energy

• Ex: as you kick a soccer ball, the energy from your leg is the same amount of energy transferred to the ball

• This is the law of conservation of energy:– Energy is neither created

or destroyed, but can only transform from one form to another

Calculating kinetic energy

• Kinetic energy is the energy an object has because of its motion

• Depends on mass and velocity

Kinetic energy = ½ (mass) (velocity)² KE = ½ mv²

• Unit of energy is called the joule (J), named for James Joule, a scientist(1 joule = 1 kg x m²/s²)

Potential Energy• Potential energy is the

stored energy of a position– Ex: a book about to fall off a

table has potential energy – if you knock it off, it will accelerate towards the ground because of gravity

• Gravitational potential energy (GPE) is the energy an object could change to kinetic energy if it falls– Depends on the mass (m)

and height (h)– GPE = (mass) (force of gravity) (height)– GPE = mgh

How are GPE and KE related?

Ex: Throwing a ball into the air• When you first throw a ball into the air, it

has kinetic energy (KE) because it is moving

• As it reaches a point in the air and stops moving, this kinetic energy changes to potential energy

• This potential energy changes to kinetic energy as the ball falls back towards the ground

Ex: Imagine you are riding a slide• At the top, you have potential energy,

before you let yourself move down the slide

• As you fall, this changes to kinetic energy because you are moving