1. What is energy? --Ability to do work!

2. Forms of energy Thermal Energy the kinetic energy of atoms and molecules (remember, “heat” is the transfer of this energy between systems) Chemical energy energy associated with electronic structure of atoms and the electromagnetic force Nuclear energy energy associated with nuclear structure of atoms and the strong nuclear force

3. Electrical energy associated with an electric current (kinetic energy of electrons in a conductor) Radiant (light) energy energy associated with photons of light Mechanical energy associated with the movement of position of physical bodies (kinetic and potential energy)

4. Energy can be categorized into two main classes:  Kinetic energy– energy a body has because it is moving

5.  Kinetic energy is a scalar quantity with unit of Joules (Newton*Meter)  Since it involves velocity, it depends on the frame of reference

6.  Potential Energy: energy that is stored in a body.  Gravitational potential energy: Energy associated with gravitational force. That is, energy that goes into lifting an object is stored in the object as gravitational potential energy.

8.  It’s a scalar quantity with unit of Joules (Newton*Meter).  Gravitational potential energy is relative because h is relative. A reference height has to be set first.  Change of gravitational energy doesn’t depend on the path, only height. (conservative forces)

9. Practice A ball of mass m collides into a stationary ball with the same mass at a velocity of v. Suppose the collision is elastic collision. a.What are the velocities of the two balls after the collision? b.What is the total kinetic energy of the system before collision? c.What is the total kinetic energy of the system after collision? d.Is the total kinetic energy conserved?

10. Practice A ball of mass m collides into a stationary ball with the same mass at a velocity of v. Suppose the collision is completely inelastic collision. a.What are the velocities of the two balls after the collision? b.What is the total kinetic energy of the system before collision? c.What is the total kinetic energy of the system after collision? d.Is the total kinetic energy conserved?

11. Momentum conserved Kinetic energy conserved Elastic collision Yes Inelastic collision YesNo Completely inelastic collision YesNo

12. Practice Drop a ball of 1 kg mass from a height of 10 meters. Compute the potential energy before it is dropped and the kinetic energy just before it hits the floor. Are they the same?