1. Energy and Work

2. Work… Work = Force // x Displacement W = F // x d ** Remember that displacement is the distance AND direction that something moves. It is a vector quantity. It has magnitude and direction. Start End Rights belong to Universal Pictures and the writers of Despicable Me.

3. Facts about Work…  Measured in Newton meters (Nm) or Joules (J)  Work is parallel to displacement  The symbol for work is W

4. Working or Not??  Work only happens if the forces acting on the object are unbalanced.  Balanced forces = NO work  Work does not happen if the object is returned to its original position.

5. Why work?  Work can change the potential energy of an object. When you lift something against the force of gravity, you are increasing the height of the object and increasing its potential energy.  The amount of work done to an object is equal to the object’s change in kinetic energy.

6. How are energy and work related?  Energy is the ability to do work  Work is done when the kinetic energy is changed  Anytime something accelerates, it is doing work

7. What is Energy?  Energy is the property that enables something to do work.

8. What is kinetic energy?  Kinetic energy is the energy of motion.  KE = 1/2 mv 2

9. What happens if… KE = 1/2 mv 2  What happens if you double the mass?  What happens if you double the velocity?  What happens when you half the mass?  What happens when you half the velocity?

10. Kinetic Energy Example… A 75 kg skater is moving at 20 m/s across the concrete. How much KE does the skater have?

11. Potential energy  Gravitational Potential Energy (PE g ) is the amount of work an object can do because of its height  Elastic Potential Energy (PE elastic ) is the amount of work an object can do because of its position

12. Gravitational Potential Energy PE g = mass (kg) x acceleration due to gravity (9.8m/s 2 ) x height (m) PE g = mgh PE g will be measure in Joules Wile E. Coyote is 2 m above the ground and has a mass of 50 kg. What is his PE g ? Who has more PE g ?

13. Now who has more PE g ?

14. Elastic Potential Energy PE elastic =1/2 kx 2 K = the spring constant (related to the strength of the spring) X = the amount the spring is stretched or compressed from equilibrium

15. Elastic Potential Energy Wile E. Coyote compressed his Acme giant spring 5 m. The instruction book stated that the spring constant is 3x10 3 N/m. How much elastic potential energy has Wile E. Coyote stored in the compressed spring?