Warm-Up 10/28/13 Compare work and power. How are they the same, and how are they different? In the stairs lab on Friday, did it take more power to go up the stairs slowly or quickly? Please turn in the stairs lab if you haven’t!

Work and Machines Monday 10/28/13

Machine Basics Machines are devices that either change the size of a force needed, the direction of a force, or the distance over which a force acts. They make work (W=Fd) easier!

Increasing Force Car jacks require you to put in a little amount of force, but applies a large force on the car

Increasing Distance When you use oars, you move a small distance, but they apply your force on the water over a much larger distance

Changing Direction Using a pulley to raise a flag reverses the direction of your force.

Downside of Machines Friction is always acting in the reverse direction of a force. Because of friction, the amount of work done by a machine is always less than the work the machine accomplishes.

Machines DO NOT decrease the total amount of work you do…they just make it easier by one of the three ways we talked about.

Work Input and Output Work Input: the work done by you on a machine =(Input Force) x (Input Distance) Work Output: the work accomplished by the machine =(Output force) x (Output Distance)

Mechanical Advantage Mechanical Advantage: the number of times that the machine increases the input force Actual Mechanical Advantage (AMA) is

Easier to measure is the Ideal Mechanical Advantage (IMA): IMA ignores friction, so it is just an estimate.

Example A woman drives her car up onto wheel ramps to perform repairs. If she drives a distance of 1.8m along the ramp to raise the car 0.3m, what is the ideal mechanical advantage of the wheel ramps? Input dist= Output dist= IMA= ?

Your Job Complete the questions on the back of this page! They are due tomorrow. QUIZ TOMORROW on Work and Power. I will provide the equations.