Chapter 14: Work, Power, & Machines

1. Chapter 14: Work, Power, & Machines Pg. 410 - 443

2. Unit 1: Work and Power Pg. 412 - 416

3. What is work? • 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 same direction as the object moves. If there is no movement, no work is done. Was any work done to lift this barbell over the weightlifter’s head? Is any work being done to keep this barbell in the air?

4. What is work? • Any part of a force that does not act in the direction of motion does no work on an object.

5. Calculating Work Work = Force [N] x Distance [m] • As the distance increases, what happens to the amount of work being done? What if it decreases? • What if the force is increased? Decreased?

6. Calculating Work Work = Force [N] x Distance [m] • The joule [J] is the SI unit of work. • When a force of 1 Newton moves an object 1 meter, 1 joule of work is done. [J]

7. What is power? • 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 in a given time, or you can do a given amount of work in less time.

8. Calculating Power • You can calculate power by dividing the amount of work done by the time needed to do the work: • What happens to power as time is increased? Decreased?

9. Calculating Power • The SI unit of power is the watt [w]. • A watt is equal to 1 Joule per second.

10. Horsepower • One horsepower [hp] is equal to about 746 watts.

11. Unit 2: Work and Machine Pg. 417 - 420

12. Machines do Work • Machines change a force to 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. Does the jack used to lift the car increase or decrease the force applied to it? Why?

13. Work Input and Output • Because of friction, the work done by a machine is always less than the work done on the machine.

14. Work Input and Output • The force you exert on a machine is called the input force. • The distance the input force acts through is known as the input distance. • The work done by the input force acting through the input distance is called the work input.

16. Work Input and Output • The force that is exerted by a machine is called the output force. • The distance the output force is exerted through is the output distance. • The work output of a machine is the output force multiplied by the output distance.

17. Unit 3: Mechanical Advantage and Efficiency Pg. 421 - 426

18. Mechanical Advantage • The mechanical advantage of a machine is the number of times that the machine increases an input force. • The actual mechanical advantage [AMA] is the ratio of the output force to the input force. In an ideal [IMA] situation, there would be no loss of force to friction. AMA is always less than IMA.

19. Unit 4: Simple Machines Pg. 427 - 435

20. Simple Machines • The six types of simple machines are: • The lever • The wheel and axle • The inclined plane • The wedge • The screw • And the pulley

21. Levers • A lever is a rigid bar that is free to move around a fixed point. • The fixed point is called a fulcrum. • The input arm is the distance between the input force and fulcrum. The output arm is the distance from the fulcrum to the output force.

22. Levers

23. Wheel and Axle • A wheel and axle is a simple machine that consists of two disks or cylinder, each one with a different radius.

24. Inclined Planes • An inclined plane is a slanted surface along which a force moves an object to a different elevation.

25. Wedges and Screws • A wedge is a V-shaped object whose sides are two inclined planes sloped toward each other.

26. Wedges and Screws • A screw is an inclined plane wrapped around a cylinder.

27. Pulleys • A pulley is a simple machine that consists of a rope that fits into a groove in a wheel.

28. Compound Machines • A compound machine is a combination of two or more simple machines which operate together.