Work, Power and Machines

1. Work, Power and Machines Mrs. Wharton’s Science Class

2. Work • In science you do work on an object when you exert a force on the object that causes the object to move some distance. • Work is done on an object when the object moves in the same direction the force in exerted. • The amount of work done on an object can be determined by using: W=FD

3. Work • Can be determined using: W=FD • The SI unit for work is the joule (J)

4. Power • Power is the rate at which work is being done on an object. • Power may also be described as the amount of work done on an object in a unit of time • P=W/T

5. How Machines Do Work

6. Machine • A device that allows you to do work in a way that is easier or more effective than if you did not use the machine. • A machine doesn’t change the amount of work you do but changes the way you do the work.

7. Machines • A machine makes work easier by changing at least one of three factors: • A machine may change the amount of force you exert • The distance over which you exert the force. • Or the direction in which you direst the force.

8. Input vs. Output • Input force- the force you exert on a machine • Output force- the force exerted by the machine • Output work=output force multiplied by the Distance • Input work= the input force multiplied by the input distance

9. Mechanical Advantage • A machine’s mechanical advantage is the number of times a machine increases a force exerted on it. • Mechanical advantage= output force/input force

10. Efficiency • The efficiency of a machine compares the output work to the input work • To calculate the efficiency of a machine, divide the output work by the input work and multiply the result by 100% • Efficiency= output work/input work x 100%