Work and Energy


1. The work done by a force is the product of the force times the distance moved by the object in the direction of the force
W = (F)(s)cos(theta)
Unit is the Joule.  1 J = 1 Nm
If force is perpendicular to the direction of motion no work is done … cos(90) = 0
The area under the Force-Distance graph is the work done. 

2. Gravity. Work done by gravity is only dependent on the vertical distance separated by the initial and final positions. It is independent of the path taken.

3. Energy is the ability to be able to do work

4. Gravitational Potential Energy … this is stored energy
Ep = mgh ; h is determined by a reference level (generally the ground)
For all systems: when an external force changes the state of a system without acceleration and does work W in the process, the work so performed is stored as potential energy in the new state of the system.

5. Kinetic Energy ... From the Greek word kinetikos, meaning motion
Ek = 1/2mv2

Work done by the net force on a body is equal to the change in the kinetic energy of the body. Know the Proof.

Work-Energy Principle: Wnet = change in Ek

6. Conservation of Energy
Eki +Epi = Ekf + Epf

Look at a pendulum

PG 112: 1 - 6, 9 - 11, 14.









Multiple Choice Questions