1. Simple Machines

2. What is a Simple Machine?
A simple machine has few or no moving parts.
Simple machines make work easier

3. Wheels and Axles The wheel and axle are a simple machine
Gears are a form of wheels and axles

4. Pulleys Pulley are wheels and axles with a groove around the outside
A pulley needs a rope, chain or belt around the groove to make it do work

5. Inclined Planes
An inclined plane is a flat surface that is higher on one end
Inclined planes make the work of moving things easier
A sloping surface, such as a ramp. An inclined plane can be used to alter the effort and distance involved in doing work, such as lifting loads. The trade-off is that an object must be moved a longer distance than if it was lifted straight up, but less force is needed. You can use this machine to move an object to a lower or higher place.  Inclined planes make the work of moving things easier.  You would need less energy and force to move objects with an inclined plane. 

6. Wedges Two inclined planes joined back to back.
Wedges are used to split things.

7. Screws
A screw is an inclined plane wrapped around a shaft or cylinder.
The inclined plane allows the screw to move itself when rotated.

8. Levers-First Class
In a first class lever the fulcrum is in the middle and the load and effort is on either side
Think of a see-saw

9. Levers-Second Class
In a second class lever the fulcrum is at the end, with the load in the middle
Think of a wheelbarrow

10. Levers-Third Class
In a third class lever the fulcrum is again at the end, but the effort is in the middle
Think of a pair of tweezers

11. Simple Machines
Simple Machines can be put together in different ways to make complex machinery

12. Simple Machines- Mechanical Advantage
Mechanical advantage (MA) is the ratio of the force put into the machine (Effort Force) to the force the machine exerts on an object (Resistance Force).
MA = Fr / Fe
MA > 1 means that the machine makes work easier and increases the amount of force applied

13. A sample problem
A worker uses a pulley to lift a 45 kg object. If the mechanical advantage of the pulley is 5.2, what is the effort force exerted by the worker?
MA = Fr / Fe
5.2 = 441 N / Fe
Effort Force = ???
Mass = 45 kg
Resistance Force = 45 * 9.8 = 441 N
Effort Force = 85 N

14. A sample problem – You try it
A worker uses a lever to lift an object with a mass of 3500 N. If the force applied by the operate was 1500 N, what is the mechanical advantage of the lever?
MA = Fr / Fe
MA = 3500 N / 1500 N
Effort Force = 1500 N
Resistance Force = 3500 N
MA = 2.33

15. Simple Machines – Ideal Mechanical Advantage
Ideal Mechanical advantage is the ratio of distance moved by the person (de ) to the distance the machine moved the object (dr ).
IMA = de / dr
LOOK AT PAGE 266 Figure 10-9

16. A Sample Problem- You Try it
A worker testing a multiple pulley system to estimate the heaviest object the system could move. When the worker moves the rope 1.5 m, the object moves 0.25 m. What is the IMA of the system?
IMA = de / dr

17. Simple Machines - efficiency
Efficiency is the ratio of work output (Wo) to work input (Wi ) multiplied by 100.
Efficiency = e = (Wo / Wi ) *100
Another way to calculate it using mechanical and ideal mechanical advantage
Efficiency = e = (MA / IMA) * 100

18. A sample problem
A man exerts a force of 310 N on a lever to raise a crate with a mass of 910 kg. If the efficiency of the lever is 78%, what is the lever’s IMA?
e = (MA / IMA) * 100
IMA = de / dr
MA = Fr / Fe
Effort Force = 310 N
Mass = 910 kg
Resistance Force = 910 * 9.8 = 8910 N
e = (MA / IMA) * 100
78 = (28.7 / IMA) *100
IMA = 36.8
MA = 8910 / 310
MA = 28.7

19. A sample problem – You Try It
A man exerts a force of 650 N on a lever to raise a crate with a weight of 1000 N. If the efficiency of the lever is 55%, what is the lever’s IMA?
e = (MA / IMA) * 100
IMA = de / dr
MA = Fr / Fe
Effort Force = 650 N
Resistance Force = 1000 N
e = (MA / IMA) * 100
55 = (1.53 / IMA) *100
IMA = 2.8
MA = 1000 / 650
MA = 1.53

20. Homework
Page 280
Problems: