Kinetic and Potential Energy

What is Energy? Remember: Work is done when a force moves an object in the same direction! The ability to do work or cause change is called energy. Scenario: wind blows a leaf off a tree. The wind causes a change in the leaf’s position, it moves a distance as a result of the force of the wind. The wind is doing work on the leaf therefore the wind has energy.

Types of Energy Two basic kinds of energy are kinetic and potential energy. Potential Kinetic Kinetic Potential

Kinetic Energy The energy of motion Examples: car driving down the road, ball rolling down hill Kinetic energy of an object depends on both its mass and velocity (speed) Kinetic energy increases as mass increases Kinetic energy increases as speed increases Example: mass: rolling a bowling ball and a golf ball down a bowling alley at the same velocity. The bowling ball has more mass than the golf ball. Traveling at the same velocity, the bowling ball will most likely be the one to knock down the pins because it has more kinetic energy. Velocity: You throw 2 equal size bowling balls down the lane. You throw one ball harder than the other so it has a greater velocity. The one that has a greater velocity (faster) has more energy transferred to it so it has more kinetic energy

Potential Energy Stored energy 2 types of potential energy: This type of energy has potential to do work Examples: toy at the top of staircase, book on bookshelf, apple on tree, stretched elastic) 2 types of potential energy: gravitational potential energy elastic potential energy

Elastic Potential Energy That can be stretched or compressed (squished) Examples: rubber band, bow and arrow, slinky, trampoline Example: archer pulling back on a bow Pulling the string changes the bow’s shape and stores elastic potential energy. The farther the string is pulled, the greater the bow’s elastic potential energy.

Gravitational Potential Energy Energy based on height Depends on height and weight The more an object weighs the greater its gravitational potential energy The greater the object’s height, the greater its gravitational potential energy

Energy Transformations Energy Transformations are when one type of energy is changed into another The Law of the Conservation of Energy states that energy cannot be created or destroyed, but can be changed from one object to another Objects can alternate between having kinetic and potential energy, or can have some of both at the same time.

Energy Transformations One of the most common energy transformations is the transformation between potential energy and kinetic energy.

Energy Transformations When you lift the marble off the ground it gets potential energy because of its height. Potential energy is greatest at the highest point

Energy Transformations As the marble moves down, Potential energy is converted into kinetic energy Kinetic energy is greatest at the lowest point

Energy Transformations The marble slows down as it goes uphill because kinetic energy is being changed back into potential energy.

Energy Transformation on a Swing 0% Kinetic 100% Potential At the top of the swing, you have all potential energy, as you swing down you change your PE into kinetic energy. At the bottom of the swing you have all KE. As you go back up KE goes back to PE On a swing or pendulum: the gravitational potential energy at the highest point is converted into kinetic as the swing or pendulum moves down; as the swing goes back up, the kinetic energy is converted back into GPE 100 % Kinetic 0% Potential

Energy Transformations with a falling object

Energy Transformation on a Roller Coaster On the roller coaster: the gravitational potential energy at the top of the hill is converted into kinetic energy as the car falls; as the car climbs the next hill, kinetic energy is converted back into gravitational potential energy

Energy Transformations On a swing or pendulum: the gravitational potential energy at the highest point is converted into kinetic as the swing or pendulum moves down; as the swing goes back up, the kinetic energy is converted back into GPE 100% Potential 100% Potential 50% potential, 50% kinetic 50% potential, 50% kinetic 100% Kinetic