1. Machines A device that makes work easier
A tool containing one or more parts that uses energy to perform an intended action.
make work easier by allowing us to push or pull over increased distances.
Increases force applied
Changes direction of force

2. In vs. Out Input force – force applied to the machine Fin
Output force – force applied by the machine Fout
Work = Force x distance
Work in = Fin x distance Fin exerted Win
Work out = Fout x distance Fout exerted Wout

3. Ideal Machines? All work in = work out Win = Wout
Fin x din = Fout x dout
No energy is “lost” to friction or elsewhere
Does NOT exist!!
Every real machine has friction
Win ≠ Wout
Input is always greater than output
Win = Wout + Wfriction

4. Efficiency Measure of how much input is used for useful work output
Efficiency (%) = work output x Wout x 100
work input Win
- Always less then 100 % in a real machine
- Output is always less than input due to frictional losses

5. The input work you do on a can opener is 24 J
The input work you do on a can opener is 24 J. The output work the can opener does is 18 J. What is the efficiency of the can opener?
Efficiency = ( output / input ) x 100 Eff = (18 J / 24 J ) x 100 Eff = 75 %

6. What is the input work when the output work is 2841 J and the efficiency is 15 %?
Efficiency = (output/ input ) x % = ( 2841 J / input ) x = ( 2841 J / input ) (input)(0.15) = (2841 J/input )( input ) (input)( 0.15 ) = 2841 J Input = 2841 J / 0.15 Input = J

7. Mechanical Advantage
Measure of the force amplification achieved by using a tool, mechanical device or machine system.
How much easier and faster a machine makes your work
Mechanical advantage = output force RMA = Fout
input force Fin
Ideal Mechanical Advantage – IMA
mechanical advantage of an ideal machine (no friction)
IMA = input distance
output distance

8. An input force of 120 N is applied to a machine to move a 720 N box
An input force of 120 N is applied to a machine to move a 720 N box. What is the mechanical advantage of the machine.
Mechanical advantage = output force / input force MA = 720 N / 120 N MA = 6

9. Using a set of pulleys, a mover raises a load a distance of 5 m by pulling in 20 m of cord. What is the ideal mechanical advantage of the system.
IMA = input distance / output distance
IMA = 20 m / 5 m
IMA = 4