Energy Chapter 9 Section 4

Energy Energy is the ability to do work or cause change What is Transfer of Energy? When an object does work on another object, energy is transferred to that second object. When energy is transferred, the object upon which work is done gains energy. The SI Unit for both Work & Energy = Joule

Kinetic Energy What is Kinetic Energy? Energy an object has due to its motion Depends on the objects MASS and its SPEED Kinetic energy increases as mass increases or if its speed increases. Kinetic Energy = ½ Mass x Speed 2

Potential Energy Stored energy that results from the position or shape of an object. Stored energy that results from the position or shape of an object. Object has the potential to do work. Object has the potential to do work.

1) Gravitational Potential Energy GPE = Weight x Height Or GPE = Mass x 9.8 m/s 2 x Height Mass must be in kilograms and Height must be in meters Does a skier have more gravitational potential energy on a 50 meter high jump or a 40 meter high jump? What is the GPE of a skier that weighs 500 Newtons and is on a 40 meter high ski jump?

2) Elastic Potential Energy When an object gains Potential energy because it is stretched or squeezed. What are some examples? Archer pulling back on an arrow changes the shape of the bow…the bow now has more potential energy that can be used to send the arrow flying

Mechanical Energy An object’s combined kinetic energy and potential energy Mechanical Energy = Kinetic Energy + Potential Energy

For example: A football weighs 4 Newtons and has a mass of.4 kg What is the football’s Kinetic Energy if it is moving at a speed of 14 m/s? Kinetic Energy = ½ Mass x Speed 2 39 Joules What is the football’s Potential Energy if it is 3 meters above the ground? Potential Energy = Weight x Height 12 Joules What is the football’s mechanical energy?

Transformation between Potential & Kinetic Energy An object that rises or falls experiences a change in its kinetic and gravitational potential energy.

The Kinetic Energy of the ball thrown into the air becomes gravitational potential energy. Its potential energy becomes kinetic energy as it falls.