Physical Science Notes

                          Work   Chapter 4

Work- applying force to make something move

            W = F * d                    Work = Force times distance

This link contains more info:    http://www.exploratorium.edu/theworld/energy/joules.html

Machine- a device that helps you do work by changing the size or direction of a force

Power- the amount of work done in a certain period of time

            P = W/t                        Power = Work divided by time

Simple Machines

Lever, crow bar

wheel & axle, doorknob

pulley, flagpole

inclined plane, wheel chair ramp

wedge, doorstop

screw, corkscrew

Mechanical Advantage

How many times the force applied to a machine is multiplied by the machine

MA =   Output / Input.

MA of Inclined Plane: length of plane / height

MA of W&A: radius of wheel / radius of axle

Ma of Pulley: number of cords supporting resistance (not cord pulled down)

Levers
Parts of a lever

Arm – portion of a lever from end to a force (effort or resistance)

Effort – force you must apply

Effort Arm –portion of the lever to which the effort is applied (from effort to fulcrum)

Resistance – Object/mass to be moved by the lever

Resistance – portion of the lever to which the resistance is applied (from resistance to fulcrum)

Fulcrum – point about which the lever rotates

There are three classes of levers

1st Class Lever

A 1^st Class lever has the Fulcrum in the middle

2nd Class Lever

A 2nd Class lever has the Resistance in the middle

3rd Class Lever

 A 3rd Class lever has the Effort in the middle

More to come…

Check your knowledge about Levers

1. Can you name the two different arms of a lever?
2. What is represented by the blue box?
3. What is represented by the red arrow?
4. What does the red portion of the lever represent?
5. What does the blue portion of the lever represent?
6. What is represented by the green triangle?
7. Why is the dotted line in the middle of the blue box?
8. What (mathematically) does a Watt (W) consist of?
9. What (mathematically) does a Joule (J) consist of?
10. What (mathematically) does a Newton (N) consist of?

Check your Answers

Answers

1. Effort Arm & Resistance Arm
2. Resistance (to be lifted)
3. Effort (put into the machine)
4. Effort Arm (Effort distance, d_e )
5. Resistance Arm (Resistance distance, d_r )
6. Fulcrum
7. it represents the center of gravity of the Blue Box
8. W = J/sec
9. J=N*m
10. N=kg*m/sec²
    

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More notes on chapter 4

Are you ready for a Worksheet?       
Levers Worksheet #2a

Lever Links

http://www.comfsm.fm/~dleeling/physics/torque.html