Sections 8.4 to 8.7

 Any object in motion is capable of doing work.  This is because a moving object has kinetic energy  Kinetic energy depends on the:  Object’s mass  Object’s velocity KE = ½ mv 2 or ½ ms 2 2

 If you throw and object, the work you do to put the object in motion will be equal to its kinetic energy.  Since: W = F x d and KE = ½ mv 2 F x d = ½ mv 2 3

 What happens to KE if you double the velocity? Triple the velocity?  How much more work do you have to do to double the speed of an object? Triple the speed?  How about stopping distance if you are driving twice as fast? Three times as fast? 4

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 Whenever work is done, it changes the energy of an object (in this case KE)  Whenever KE changes, work must be done.  So: W = ∆E 6

 It is important to understand how energy transforms.  If Joe climbs on a lab table, he does work, which is transformed into PE.  If he jumps off the table, the PE is transformed to KE.  If Joe jumps onto a see-saw and Aslan is standing on the other end, Joe’s KE is transformed to Aslan’s KE.  If Aslan ends up on top of another lab table, his KE is transformed to PE 7

 Energy may be transformed, but this is done with no net loss or net gain.  However, it may be transformed into different forms of energy.  If Joe’s KE had been transformed to heat in the see saw and heat in his shoes in addition to KE for Aslan, is it likely that Aslan will have enough KE to reach the top of the lab table? 8

 The Law of Conservation of Energy states: Energy cannot be created nor destroyed. It can be transformed from one form to another, but the total amount of energy never changes. 9

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 A machine is device used to muliply forces or change the direction of forces.  One of the simplest machines is a lever.  We do work on one end of a lever.  The other end of the lever does work on the object.  If we push down on the lever, the object will move up. 11

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Work input = Work output So (Force x distance) input = (Force x distance) output 13

 If the pivot point of the lever is close to the object, then:  A small input force exerted over a long distance will result in:  A large output force exerted over a short distance. 14

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 For a machine like a lever:  If your input force is 15 N and your output force is 60 N your mechanical advantage is: 17

 There are 3 ways to set up a lever: 18

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 A pulley is a lever that changes the direction of the force.  Pulley systems can multiply forces  A single pulley is a Type 1 Lever. 22

 Changes direction of the force  Fulcrum is the axis (axle) of the pulley  Mechanical advantage = 1 23

 In this case the pulley is acting as a Type 2 Lever  The type of system has a mechanical advantage of 2 24 Input fulcrum output

 For simple pulley systems, the mechanical advantage is equal to the number of strands that actually support the load. 25

1 stands support the load – M.A. =12 stands support the load – M.A. =2 26

Load moves half as much – effort halved.  Again in this simple pulley system there are 2 strands holding the load, so the M.A. = 2 27

When you pull 4 m the load moves 1m – M.A. = 4  Applied force x input distance = output force x output distance  You can also find M.A. in this situation by taking input distance/output distance 28

 No machine can create energy.  Machines can only transfer energy or transform it from one form to another.  Machines can give you a mechanical advantage. 29