Energy in Motion 8SCIENCE

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