# Today’s Agenda…9-16 Bellringer: What are the two conditions that must be met for something to be work? Finish notes on Work (Study Pack #17) Practice calculating.

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Today’s Agenda…9-16 Bellringer: What are the two conditions that must be met for something to be work? Finish notes on Work (Study Pack #17) Practice calculating Work Notes on Machines (Study Pack #18) Upcoming: Test next week and study packs due! Start getting your notes together!

Study Pack #18 Machines

Today’s Goals! I can explain how machines make work easier. I can explain the effect of friction on machines.

What is a machine? A device that makes work easier or more effective Examples: – Bulldozer – Shovels

What is a machine? A machine does not change the AMOUNT of work you do A machine changes the way in you do work

What is a machine? A machine makes work easier by changing: – the amount of force you exert – the distance over which you exert the force – the direction in which you exert your force

What is a machine? When you do work with a machine you exert a force The force you exert on the machine is called the input force Example: you exert a force on the handle when you use a shovel to lift dirt

What is a machine? The machine then does work The force exerted by the machine is called the output force

Multiplying Force In some machines, the output force is greater than the input force A decrease in force, must mean an increase in distance You will apply less force but over a larger distance In the end, you do as much work with the machine as you would without the machine, but the work is easier to do

Multiplying Force For example: a ramp – You need to lift a piano – You can lift it vertically or you can push it up a ramp – The distance you have to exert a force is longer because the length of the ramp is greater than the height of the stage – But, the advantage is that the force is much smaller! – So it has made your work easier!

Multiplying Distance In some machines the output force is less than the input force These machines allow you to exert your input force over a much shorter distance But, you have to apply a greater force!

Multiplying Distance For example: a paper fan – When you fold up a sheet of paper and move it back and forth to fan yourself your hand is moving a much shorter distance than the fan

Changing Direction Some machines change the direction of the input force

Changing Direction Example: a pulley system – Raising a sail on a boat – It is much easier to pull downward than to lift up

Work In and Work Out In an “ideal or perfect machine” the work done by your input force would also be done by the output force In real machines friction occurs as one part moves past another Friction causes some of the input work to be changed into heat, which can’t be used to do work For a real machine the work out will always be less than the work in

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