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# Work and Machines - PowerPoint PPT Presentation

Work and Machines. Machines Do Work. A Machine is a device that changes a force. Ex. A Jack used to change a tire. Machines make work easier to do. They change the size of a force needed The direction of a force The distance over which a force acts. Machines Do Work.

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## PowerPoint Slideshow about ' Work and Machines' - tori

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Presentation Transcript

### Work and Machines

• A Machine is a device that changes a force.

• Ex. A Jack used to change a tire.

• Machines make work easier to do.

• They change the size of a force needed

• The direction of a force

• The distance over which a force acts

• The more Force applied, the shorter the overall distance.

• Ex. Carry 5 books at the same time from Mrs. Larose's class to Mrs. Hendee’s class.

• The less force applied, the longer the overall distance.

• Ex. Carry one book at a time from Mrs. Larose's class to Mrs. Hendee’s class

• Change in direction of applied force.

• Ex. Pulling back on the handle of a oar causes its other end to move in opposite direction.

• If the oar is pushed father away from the boat, how will the force needed to pull the oar through the water change?

• A rower pulls back on each oar handle and the other end of the oar pushes against the water.

• Work is done on the oar (Machine) by pulling on them, and the oars do work on the water to move the boat.

• Because of friction, the work done by a machine is always less than the work done on the machine

• The force you exert on a machine is called input force.

• The distance the input force acts through is called input distance.

• The work done by the input force acting through the input distance is called work input.

• Formula:

• Work input= Input force x input distance

• The force that is exerted by a machine is called output force.

• The distance the output force is exerted through is called output distance.

• Formula:

• Work output= output force x output distance

• If there is no change in work input, there cannot be an increase in the work output.

• You cannot get more work out of a machine than you put into it!

• The mechanical advantage of a machine is the number of times that the machine increases an input force.

• The relation of input force used to operate a machine and the output force exerted by the machine depends on the type of machine and how it is used.

• Ex. A nutcracker

• The mechanical advantage determined by measuring the actual forces acting on a machine is the actual mechanical advantage

• Formula:

• Actual mechanical advantage= Output force

Input force

Ex. Long incline ramp

• The ideal mechanical advantage of a machine is the mechanical advantage in the absence of friction.

• Because friction is always present, the actual mechanical advantage of a machine is always less than the ideal mechanical advantage.

• Formula:

• Ideal mechanical advantage= Input distance

Output distance

• A woman drives her car up onto wheel ramps to perform some repairs. If she drives a distance of 1.8 meters along the ramp to raise the car 0.3 meter, what is the ideal mechanical advantage of the wheel ramp?

• The percentage of the work input that becomes work output is the efficiency of a machine.

• Because there is always friction, the efficiency of any machine is always less than 100%.

• The work output of a machine is always less than the work input.

• Formula:

• Efficiency= (Work input / Work output) x 100%

• You have just designed a machine that uses 1000J of work from a motor for every 800J of useful work the machine supplies. What is the efficiency of your machine?