Notes: Machines CW: Man & Machines H: Simple Machines
Notes: MachinesCW: Man & MachinesH: Simple Machines
Machines
April 15, 2009
Objectives
1. Explain how a machine makes work easier
2. Calculate mechanical advantage3. Describe an ideal machine 4. Explain why machines are not
100% efficient
History of Work
Simple Machines
Machines make work easier.
W = F x D
The two most common resistive forces are friction and gravity
Machines
Simple Machines
a device that does work with only one a device that does work with only one movementmovement
Types of Simple Machines
1. inclined plane2. wedge 3. lever4. wheel & axle5. screw6. pulley
These make work
easier !
Machines make work easier by changing
1. the amount of force you exert
2. the distance over which you exert your force
3. the direction over which you exert your force
when using a machine to do work
Effort (Input) Force (FE) –the force you apply to the machine
Resistance (Output) Force (FR) –the force that the machine applies
2 forces involved
Work In (Win) – The work done on the machine (energy put into the machine)
Work Out (Wout) – The work done by the machine (energy put out by the machine)
2 types of work involved
Mechanical Advantage
The number of times a machine increases a force exerted on it
MA = output force / input force
Machines make work easier by changing
1. the amount of force you exertthe MA is greater than 1
2. the distance over which you exert your force the MA is less than 1
3. the direction over which you exert your force
the MA is equal to 1
Efficiency
Compares the output work to the input work.
Efficiency = Wout x 100%
Win
The higher the percent, the more efficient the machine.
one in which there is no friction, no energy is lost so Win=Wout
In reality, work out will always be less than work in because energy is lost through friction
Ideal machineIdeal machine