1. Chapter 4: Work and Machines

2. Work is defined as a force being applied over a distance
Work is defined as a force being applied over a distance. In other words, a force is acting on an object, causing it to move a certain distance. You must move something in order to do work!

3. Work is not necessarily done every time a force is applied!
Examples: pushing on a wall, holding a heavy object, carrying something

4. The formula for calculating work is:
Work = Force x Distance

5. Because Force is measured in N and Distance is measured in meters, the unit of work is Newton-meters (N-m).
In the metric system, work is measured in Joules (J)

6. Power is the rate at which work is done
Power is the rate at which work is done. It is the amount of work per unit of time. Power tells us how fast work is being done.
Formula: Power = Work / Time
OR Power = (Force x Distance) / Time

7. The unit of measurement for Power is the watt (W)
The unit of measurement for Power is the watt (W). One watt is equal to 1 Joule per second (1 W = 1 J/sec)
Example: a 50-watt light bulb does work at the rate of 50 Joules per second

8. An instrument that makes work easier is called a machine
An instrument that makes work easier is called a machine. A machine is any device that helps you do something.

9. There are 2 types of work involved in using a machine:
1. work that goes into the machine
2. work that comes out of the machine

10. Work input is the force that is applied to the machine, or the input force. Every machine must have some work input in order to function.

11. Work output is the work done by the machine
Work output is the work done by the machine. This is the output force that the machine applies.

12. Machines do make work easier because they change either the size or the direction of the force put into the machine.

13. The operation of any machine always involves some type of friction
The operation of any machine always involves some type of friction. Some of the machine’s work is used to try to overcome the force of friction.

14. Machines with the smallest amount of friction are the most efficient.
Efficiency is the comparison of work input to work output for a machine.
Machines with the smallest amount of friction are the most efficient.

15. The number of times a machine multiplies force is called the mechanical advantage of the machine. The greater the mechanical advantage, the easier it is to do the job.

16. The six types of simple machines are: inclined plane, wedge, screw, lever, pulley, and wheel and axle.
All machines are made from one or more of these!

17. Lever: a rigid bar that moves freely around a fixed point
Lever: a rigid bar that moves freely around a fixed point. This fixed point is called the fulcrum.
Example: crowbar, bottle opener, fishing pole

18. Pulley: rope, belt, or chain wrapped around a wheel. 2 types:
1. fixed pulley: changes the direction of the effort force
2. moveable pulley: moves with the resistance force

19. Wheel and Axle: consists of two circular objects of different sizes
Wheel and Axle: consists of two circular objects of different sizes. The larger object is called the wheel, the smaller is the axle. Depending on the difference in size, the force will be multiplied!
Examples: gears, door knobs, steering wheel

20. Inclined plane: a flat slanted surface that is used to raise a heavy object. These decrease the amount of force needed to move the object, but increase the distance to travel.
Example: ramps, stairs

21. Wedge: an inclined plane that moves
Wedge: an inclined plane that moves. The thinner a wedge is, the less effort force is needed to overcome the resistance force.
Example: ax, zipper (3 wedges), knife

22. Screw: inclined plane that is wrapped around a cylinder
Screw: inclined plane that is wrapped around a cylinder. As a screw rotates, it moves a certain distance up or down.
Example: wood screw, cork screw, jar lid

23. Compound Machine: any machine that uses 2 or more simple machines.
Examples: bicycle, car