1. HOW MACHINES DO WORK? Key Concepts How do machines make work easier? What is a machine’s mechanical advantage? How can you calculate the efficiency of a machine?

2. Key Terms  Machine  Input force  Output force  Input work  Output work  Mechanical advantage  efficiency

3. What is a Machine?  A device that allows you to do work in a way that is easier 1. changing the amount of force needed 2. changing the distance over which force is exerted 3. changing the direction in which the force is exerted

4. Input and Output Forces  Input Force – the force you exert on the machine – makes machine move a certain distance called input distance  Output Force – the force the machine exerts over a certain distance called the output distance

5. Input and Output Work  Input force times input distance = input work  Output force times output distance = output work  Output work can never be greater than input work

6. Changing Force  When a machine increases force, you must exert the input force over a greater distance

7. Changing Distance  When a machine increases distance, you must apply a greater input force

8. Changing Direction  When a machine changes the direction of the input force, the amount of force and the distance remain the same

9. Mechanical Advantage  Number of times a machine increases a force exerted on it  Mechanical advantage = Output force Input force

10. Increasing Force  When output force is greater than input force, the mechanical advantage is greater than 1 You exert a force of 10N on a hand held can opener. It exerts an output force of 30 N.  MA = Output force = 30N = 3 Input Force 10 N The can opener triples your force

11. Increasing Distance  For a machine that increases distance the output force is less than the input force and the mechanical advantage is less than one  If the input force is 20N and the machine’s output force is 10N  MA = Output force = 10N = 0.5 Input force 20N

12. Changing Directions  For a machine that changes the direction of the force, the input and output forced are the same and the mechanical advantage is 1

13. Efficiency of Machines  In an ideal situation the work done on machine = the work done by the machine  In real situation the output work is always less than the input work

14. Friction and Efficiency  The less friction there is, the closer the output work is to the input work  Efficiency of a machine compares the output work to the input work  Efficiency is expressed as a percent

15. Calculating Efficiency  Efficiency = Output Work X 100% Input Work  What is the efficiency of a machine that gives 30 joules of work for every 100 joules put into it?  What is the efficiency of a machine that gives 20 joules of work for every 50 joules put into it?