simple machines2008

Simple MachinesSimple Machines

May 9, 2008May 9, 2008

ObjectivesObjectives

1.1. Explain how a machine makes Explain how a machine makes work easierwork easier

2.2. Calculate mechanical advantageCalculate mechanical advantage

3.3. Describe an ideal machine Describe an ideal machine

4.4. Explain why machines are not Explain why machines are not 100% efficient 100% efficient

History of WorkHistory of Work

Before engines and motors were invented, people had to do things like lifting or pushing heavy loads by hand. Using an animal could help, but what they really needed were some clever ways to either make work easier or faster.


Ancient people invented simple machines that would help them overcome resistive forces and allow them to do the desired work against those forces.

Machines make work easier by changing the size and/or the direction of the force• In order for work to be done:

– A force must be exerted– There must be movement in direction of the force

The two most common resistive forces are friction and gravity

MachinesMachines

Machines make work easier Machines make work easier by changing by changing

1.1. the amount of the amount of forceforce you exert you exert

2.2. the the distancedistance over which you exert over which you exert your forceyour force

3.3. the the directiondirection over which you over which you exert your forceexert your force


a device that does work with only one movement

Types of Simple MachinesTypes of Simple Machines

1. inclined plane2. wedge 3. lever4. wheel & axle5. screw6. pulley

These make work

easier !

when using a machine to do workwhen using a machine to do work

• Effort (Input) Force (FEffort (Input) Force (FEE)) – This is the – This is the force you apply to the machineforce you apply to the machine

• Resistance (Output) Force (FResistance (Output) Force (FRR)) – This – This is the force that the machine appliesis the force that the machine applies

2 general forces involved2 general forces involved

Work In (WWork In (Winin) ) – The work done on – The work done on the machine (energy put into the the machine (energy put into the machine)machine)

Work Out (WWork Out (Woutout) ) – The work done by – The work done by the machine (energy put out by the machine (energy put out by the machine)the machine)

2 types of work involved2 types of work involved

•WWinin= F= Fee x D x Dee

•WWoutout= F= Frr x D x Drr

Mechanical AdvantageMechanical Advantage

The number of times a machine The number of times a machine increases a force exerted on itincreases a force exerted on it

MA = output force / input forceMA = output force / input force


When the output force is greater than When the output force is greater than the input force, the MA is the input force, the MA is greatergreater than than 11..

If you exert an input force of 10 N on a If you exert an input force of 10 N on a can opener, and the can opener exerts can opener, and the can opener exerts an output force of 30 N, the can opener an output force of 30 N, the can opener has a MA of 3.has a MA of 3.


For a machine that increases distance, For a machine that increases distance, the output force is less than the input the output force is less than the input force. So the MA is force. So the MA is lessless than 1than 1..

If you exert an input force of 20 N and If you exert an input force of 20 N and the machine’s output force is 10 N, the the machine’s output force is 10 N, the MA is 0.5MA is 0.5

The machine only exerts half of your The machine only exerts half of your force but it is exerted over a loner force but it is exerted over a loner distance.distance.


If only the direction changes, the If only the direction changes, the input force will be the same as the input force will be the same as the output force. The MA will output force. The MA will always be always be 11..

EfficiencyEfficiency

Compares the output work to the Compares the output work to the input work.input work.

Efficiency = Efficiency = WWoutout x 100%x 100%

WWinin

The higher the percent, the more The higher the percent, the more efficient the machine.efficient the machine.

one in which there is no friction, no one in which there is no friction, no energy is lost so work in and work out energy is lost so work in and work out would be equalwould be equal

• WWinin=W=Woutout FFee x D x Dee = F = Frr x D x Drr

In reality, work out will always be less In reality, work out will always be less than work in because energy is lost than work in because energy is lost through frictionthrough friction

Ideal machineIdeal machine

simple machines2008

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