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Simple MachinesSimple Machines

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History of WorkHistory of Work

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

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Simple MachinesSimple Machines

Ancient people invented simple Ancient people invented simple machines that would help them to do machines that would help them to do the desired work for difficult tasks. the desired work for difficult tasks.

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Simple MachinesSimple Machines

Machines can make work easier by Machines can make work easier by increasing the force that can be increasing the force that can be applied to the objectapplied to the object

A bottle opener increases the force you A bottle opener increases the force you can apply to a bottle cap, causing the can apply to a bottle cap, causing the cap to bendcap to bend

A car jack enables you to lift a heavy A car jack enables you to lift a heavy machinemachine

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Machines can make work easier by Machines can make work easier by increasing the distance which a force increasing the distance which a force can be applied.can be applied. A rake and a ramp make work easierA rake and a ramp make work easier

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Machines can also make work easier by Machines can also make work easier by changing the direction of the applied forcechanging the direction of the applied force

When you open a window blind by When you open a window blind by pulling down on the cord, the downward pulling down on the cord, the downward force on the cord is changed to an force on the cord is changed to an upward force that opens the blinds.upward force that opens the blinds.

An ax blade changes the direction of the An ax blade changes the direction of the force from vertical to horizontal splitting force from vertical to horizontal splitting the wood. the wood.

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Effort and ForceEffort and Force

Two forces are involved when a machine Two forces are involved when a machine is used to do workis used to do work

Effort force (FEffort force (Fee) the force applied to the ) the force applied to the

machinemachine

Resistance force (FResistance force (Frr) the force applied by the ) the force applied by the

machinemachine

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Effort and ForceEffort and Force

Pulling out a nail with a hammer.Pulling out a nail with a hammer.

You apply the effort force on the handleYou apply the effort force on the handle The resistance force is the force the claw The resistance force is the force the claw

applies to the nailapplies to the nail

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Mechanical AdvantageMechanical Advantage The number of times a machine multiplies the The number of times a machine multiplies the

effort force is the mechanical advantage (MA) of effort force is the mechanical advantage (MA) of the machinethe machine

If a machine increases an input force of 10 pounds If a machine increases an input force of 10 pounds to an output force of 100 pounds, the machine has to an output force of 100 pounds, the machine has a mechanical advantage (MA) of 10. a mechanical advantage (MA) of 10.

In machines that increase distance instead of force, In machines that increase distance instead of force, the MA is the ratio of the output distance and input the MA is the ratio of the output distance and input distance.distance.

MA = output/input MA = output/input

EfficencyEfficency

Machines that loose less energy to friction Machines that loose less energy to friction are said to be efficient.are said to be efficient.

Efficency is a measure of how much of the Efficency is a measure of how much of the work put into a machine is changed into work put into a machine is changed into useful out put work by the machineuseful out put work by the machine

A machine with a high efficency produces A machine with a high efficency produces less heat from the friction so more of the less heat from the friction so more of the input work is changed into useful output input work is changed into useful output work work

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Work done by machinesWork done by machines

When you use a crowbar to pry the lid off When you use a crowbar to pry the lid off a wooden crate, you are trying to move a wooden crate, you are trying to move something that resists being moved. something that resists being moved.

You are working against the friction You are working against the friction between the nails in the lid and the crate. between the nails in the lid and the crate.

If you use a crowbar to move a rock, you If you use a crowbar to move a rock, you would be working against gravity.would be working against gravity.

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Conserving energyConserving energy

Energy is always conserved. Energy Energy is always conserved. Energy cannot be created or destroyed.cannot be created or destroyed.

A machine can not create energy so…A machine can not create energy so… W out is never greater than W in.W out is never greater than W in.

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The machine does not transfer all of the The machine does not transfer all of the energy it receives to the object.energy it receives to the object.

When a machine is used , some of the When a machine is used , some of the energy transferred changes to heat due to energy transferred changes to heat due to friction.friction.

The energy that changes to heat cannot The energy that changes to heat cannot be used to do work so…be used to do work so…

W out is always smaller than W inW out is always smaller than W in

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Ideal machineIdeal machine

If there was a perfect machine built in If there was a perfect machine built in which there was no friction then none of which there was no friction then none of the input work or output work would be the input work or output work would be converted to heat.converted to heat.

So for an ideal machineSo for an ideal machine W in =W outW in =W out

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