1. Ch. 5 Simple Machines

2. Machines
Machines: make work easier by changing the size or direction of a force (they do not save work)
If they did what law would this violate?
A simple machine has few or no moving parts.

3. Work W= F x D Effort force (Fe) applied to machine Or Input force Fin
Resistance force (Fr) Force applied by the machine
Or Output force Fout
Work done on the machine is work input
Win
Work done by the machine is work output
Wout
An ideal machine would not lose any energy
Or Work in= work out

4. Mechanical advantage
We use machines to gain mechanical advantage- divides the force up over a greater distance
Mechanical Advantage is how much the machine multiplies the effort force.
MA= resistance force/effort force
Ideal vs. Actual

5. Stuff to know AMA- actual mechanical advantage
AMA=Resistance force/Effort force
Work in= Effort force x Effort distance
Work out= Resistance force x Resistance distance
IMA- Ideal mechanical advantage
IMA = different for different machines

6. practice
You use a 50N force on a crowbar to open a crate with a resistance force or 900N. What is the MA.
What is the effort force needed to lift a 2000N rock with a jack that has a MA of 12?
What does our triangle look like?
Do we always use machines to increase mechanical advantage?

7. Levers The Lever pivots on a fixed point called the fulcrum
Effort arm is the piece of the lever where force is applied
The resistance arm is the piece of the lever with the resistance or load

8. Levers have mechanical advantage as well
Ideal mechanical advantage assumes no friction
For levers IMA = length of effort arm/ length of resistance arm

9. Lever Practice
You use a lever with an 80cm effort arm and a resistance arm of 10cm to lift a 240N object.
What is the IMA of the lever?
How much force do you need to apply to raise the object?

10. Effeciency
Efficiency is how much of the work put into the machine becomes work put out by the machine. We strive for higher efficiency.
The efficiency of a machine can be found in two ways
eff = AMA/IMA x 100%
eff = work out/work in x 100%

11. Problem
Example: An inclined plane 4m long is used to lift a piano weighing 1500 n onto the back of a truck 2m off the ground. A force of 900n was needed to push the piano up the inclined plane. (A) What was the work in?
W in = 900n x 4 m = 3600 J
(B) What was the work out?
Wout = 1500 n x 2 m = 3000 J
(C) What was the IMA of the inclined plane? IMA = length/height = 4/2=2
(D) What was the AMA of the inclined plane?
AMA = R/E = 1500 n/900n = 1.67 (E) What was the efficiency?
eff = 1.67/2 = 83.5% or
eff = 3000 J/ 3600 J = 83.3 %

12. Power
W= F x d
Power is the rate of doing work or how fast the work is done.
To calculate power
Power = Work/time
P = W/t
The unit of power is J/s
renamed the watt after James Watt.

13. Power
Ex. If a student weighing 70 N runs up a flight of steps 25 m high in 3.5 seconds, what is his power?
W = Fd = (70N)(25 m) = 1750 J
P = 1750 J/3.5 s = 500 W or .5 kW
1kW = 1000 W