1. Work & Simple Machines

2. What is WORK?

3. What is WORK?
Work is done when an object moves in the same direction as the applied force.
If there is no movement, there is no work
The formula for work is: W = Force x distance
Work is a transfer of energy from one object to another

4. What is a machine?

5. What is a machine? A device to make work easier.
A machine does NOT decrease the amount of work, it just changes the way work is done.

6. What is a compound (or complex) machine?
A machine made up of two or more simple machines.

7. How do machines make work easier if they do not change the amount of work?

8. Machines make work easier by changing…
The size of the force
The distance over which the force is applied
The direction the force
MORE

9. Any change in the size of the force changes the distance
Any change in the size of the force changes the distance. No machine can increase both force and distance.
FORCE = DISTANCE
FORCE= DISTANCE

10. Force/Distance Trade Off!
If you increase the force, you decrease the distance (Raking leaves)
If you increase the distance, you can decrease the force. (Ramp)
Or, they leave force and distance alone but change the direction in which the load moves. (Raising a flag)

11. All machines have an input and output force!
Input force= the force you exert on the machine (your hands on the rake)
Output force= the force the machine exerts on an object (the rake on the leaves)

12. What is mechanical advantage?

13. What is mechanical advantage?
The number of times a machine multiplies the effort or input force
How well a machine works or how useful it is to you

14. Mechanical Efficiency
A measure of the effectiveness of a machine; compares the input force to the output force
A machine CANNOT be 100% efficient because the moving parts on a machine produce friction and energy is lost as heat

15. What are the 6 types of simple machines?
The lever, the pulley, and the inclined plane The wheel and axle, the wedge, and the screw are modifications of these simple machines.

16. 1. LEVER
A simple machine made with a bar that pivots (move) around a fixed point called a fulcrum
Low Mechanical Advantage
High Mechanical Advantage
3rd class levers
Fulcrum – effort – load
1st and 2nd Class levers
Fulcrum and load closer together

17. The 3 types of levers:
A first class lever has the fulcrum in the center
A second class lever has the output/load in the center
A third class lever has the input in the center
MORE

18. Diagrams of Levers
Effort force = input force
Load – output force

19. Diagrams of Levers

20. Low Mechanical Advantage High Mechanical Advantage
2. PULLEY
A simple machine made with a rope or chain wrapped around a grooved wheel
A pulley changes the direction of the force OR the size of the force
Low Mechanical Advantage
High Mechanical Advantage
Single/Fixed pulley
1 wheel/1 rope segment
Block and tackle pulley
Multiple wheels/multiple rope segments

21. Diagrams of Pulleys Fixed pulley: Movable Pulley:
Movable Pulley:

22. Low Mechanical Advantage High Mechanical Advantage
3. Wheel and Axle?
A wheel and axle consists of 2 circular objects of different sizes.
Example: faucet, pencil sharpener, door knob
Low Mechanical Advantage
High Mechanical Advantage
Large axle compared to the wheel
Small axle compared to the wheel

23. Diagram of Wheel & Axle

24. 4. Inclined plane
A simple machine with no moving parts. It is simply a straight slanted surface. ( Ex. a ramp.)
Low Mechanical Advantage
High Mechanical Advantage
Short distance, increased force
Longer distance, decreased force

25. Low Mechanical Advantage High Mechanical Advantage
5. Wedge
A modification of an inclined plane that moves .
It is made of two inclined planes put together.
Low Mechanical Advantage
High Mechanical Advantage
Dull, wide edge
Sharp, thin edge

26. 6. Screw An inclined plane that wraps around a cylinder.
Low Mechanical Advantage
High Mechanical Advantage
Threads far apart
Threads close together

27. Go to this link for more information about machines
Go to this link for more information about machines. Remember to hit the “back” button on your browser to return to this slide show.