MachinesMachines: 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.

WorkW= F x DEffort force (Fe)

applied to machineOr 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

Mechanical advantageWe 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

Stuff to knowAMA- actual mechanical advantageAMA=Resistance force/Effort forceWork in= Effort force x Effort distanceWork out= Resistance force x Resistance

distanceIMA- Ideal mechanical advantageIMA = different for different machines

practiceYou 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?

LeversThe 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

Levers have mechanical advantage as well

Ideal mechanical advantage assumes no friction

For levers IMA = length of effort arm/ length of resistance arm

Lever PracticeYou 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?

EffeciencyEfficiency 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 befound in two ways

eff = AMA/IMA x 100%eff = work out/work in x 100% 

Problem

Example: An inclined plane 4m long is used to lift a piano weighing1500 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 inclinedplane? IMA = length/height = 4/2=2

(D) What was the AMA of theinclined plane?

AMA = R/E = 1500 n/900n = 1.67(E) What was the efficiency?

eff = 1.67/2 = 83.5% oreff = 3000 J/ 3600 J =

83.3 %

Power W= F x dPower is the rate of doing work or how

fast the work is done.To calculate powerPower = Work/timeP = W/tThe unit of power is J/s renamed the watt after James Watt.

PowerEx. 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 JP = 1750 J/3.5 s = 500 W or .5 kW1kW = 1000 W