1. Bell Question 1/23/12 What force makes machines less efficient?
What is the equation for measuring efficiency?
What is the efficiency of a machine that has an output of 600 J when 800 J of work are put into the machine?

2. Inclined Plane
A flat sloped surface

3. How it works: exert a force over a longer distance
Mechanical advantage : divide the length of the incline by its height.

4. Wedge
A device thick at one end and tapers to a thin edge at the other end.

5. How it works: move inclined plane turns the output force at 90° angle
Mechanical advantage : length of the wedge divided by the width.

6. Screw
An inclined plane wrapped around a cylinder

7. How it works: threads increase the distance over which you exert the input force, output force pulls the screw into the object.
Mechanical advantage: the closer the threads the greater the M.A. , Length around the threads divided by the length of the screw.

9. Bell Questions 1/25/12
A _____________ is a device that is thick at one end and tapers to a thin point at the other end.
A __________ is an inclined plane wrapped around a cylinder.
What is the ideal mechanical advantage of this inclined plane?
8 m
2 m

10. LEVER
Lever – a rigid bar that is free to pivot, or rotate on a fixed point (fulcrum)
Mechanical advantage = distance to input
distance to output

11. 1st Class Lever – Change the direction of input force
1st Class Lever – Change the direction of input force. The fulcrum is between the output force and input force.

12. 2nd Class Lever – increase the force, they don’t change the direction of the force. (output force in the middle)

13. 3rd Class Lever – increase distance, don’t change direction
3rd Class Lever – increase distance, don’t change direction. (input force in the middle)

16. Bell Questions 1/30/12
You exert a force of 25 newtons to push a box 10 meters. How much work did you do on the box?
An ideal machine would have an efficiency of _______%.
If scissors have an efficiency of 60%, 40% of your work is lost due to what force?

17. Wheel and Axle
two cylindrical objects fastened together and rotate on a common axis
Large radius is the wheel, small radius is the axle.

18. How it works – increases force, must exert force over a longer distance
Mechanical advantage = Radius of wheel
Radius of axle

20. Pulley
grooved wheel with a rope or cable.

21. How it works – increases the effect of your input force and changes direction of input force.
Mechanical advantage - number of sections of rope that support the object.

22. Fixed pulley – does not change the amount of force applied, only changes direction
Moveable pulley – increase amount of force applied, does not change direction
Block and tackle – both fixed and moveable pulleys

24. Bell Questions 1/31/12
Name the six kinds of simple machines (see if you can do it without looking in your notes or your book)

25. Compound Machine – a device that combines two or more simple machines.
Examples
Wheel barrow
Scissors
bicycle