1. Wheels, Gears, & Pulleys

2. Wheels, Gears, & Pulleys
In many cases, a lever’s motion is restricted. In other words, it cannot continue rotating around and around.
Examples: seesaw, wheelbarrow, nail clippers
Other simple machines do not have this limitation

3. Wheels, Gears, & Pulleys

4. Wheel and Axle
a rotating object where the force is applied at some distance from the axis
This turning force creates a moment or torque.

5. Wheel and Axle
The effort arm is the distance from the center to the applied force.
The resistance arm is the distance from the center to the resistance.

6. effort arm
resistance arm

7. resistance arm
effort arm

8. Wheel and Axle
Any device with a handle that turns in a circular direction is most likely a wheel and axle.
Examples: can openers, garden hose reels, fishing rods

9. Wheel and Axle
IMA =
effort arm
resistance arm

10. Wheel and Axle
God is the creator of the wheel and axle. It is found in created organisms as “simple” as a bacterium.

11. Wheels, Gears, & Pulleys

12. Gears
Gears are wheel and axle combinations with notches or teeth around the circumference.
Note that when two gears touch, they always turn in opposite directions.

13. Gears
The IMA of 2 gears can be determined by the ratio of the number of teeth with the following formula:
IMA =
resistance gear teeth
effort gear teeth

14. Gears
effort
resistance
IMA = 13 21
= 0.62
increases speed

15. Gears
resistance
effort
IMA = 21 13
= 1.62
decreases speed

16. Gears Gears can also change the direction of motion. Ex: differential
Gears can be combined into systems that can be very complex.
Ex: transmission

18. Wheels, Gears, & Pulleys

19. Pulleys
A pulley is a wheel with a groove containing a rope or cable.

20. Pulleys
The effort arm length and resistance arm length are the same—the distance from the center to the outside of the pulley.

21. Pulleys A single fixed pulley has an IMA of 1.
Why then would we use it?
Because you can use your weight to lift the object.

23. Pulleys A single moveable pulley has an IMA of 2.
The rope is supported at both ends, so only half of the weight is at each end.

26. Pulleys
A group of pulleys working together is called a pulley gang or a block and tackle.

28. Pulleys
To find the IMA of a pulley gang, count the number of ropes which support the load. Do not count the section of rope which supplies the effort.
Block and tackles greatly increase the effectiveness or MA of pulleys.

29. What is the MA of this block and tackle?
One
Two
Three
Four

30. What is the MA of the gears shown, if the smaller gear is the effort gear?
0.4
0.5
2.0
2.5

31. Which of the following is not a modified form of a wheel and axle?
Gear
Screw
Reel
Pulley