1. Ch14 Concepts Efficiency Work Work Power Power Machines Machines 1

2. Work is the product of force and distance For a force to do work on an object, some of the force must act in the direction the object moves. For a force to do work on an object, some of the force must act in the direction the object moves. No movement=no work done work=force X distance SI unit of work is the Joule (J) SI unit for force is the newton (N) SI unit for distance is the meter (m)

3. Power is the rate of doing work. Doing work at a faster rate requires more power. To increase power, you can increase the amount of work done, or you can do a given amount of work in less time. Power= Work/Time The SI unit of power is the watt (W) The SI unit of time is the second (s) 1 Watt= 1 j/sec 3

4. What is a machine? A machine is a device that changes a force They make work easier to do. They change the size of a force needed, the direction of a force, or the distance over which a force acts 4

5. Efficiency The percentage of work input that becomes work output is the efficiency of a machine Because there is always some friction, the efficiency of any machine is less than 100% It is expressed as a percentage Efficiency =work output/work input X 100% 5

6. Simple Machines Six different types: Lever Lever Wheel and axle Wheel and axle Inclined plane Inclined plane Wedge Wedge Screw Screw pulley pulley 6

7. Mechanical Devices Many are made of combinations of two or more of the six different types of simple machines A compound machine is a combination of two or more simple machines that operate together. Ex. Car, washing machine, clocks, etc. 7