## Final Exam Chapter 14: Work, Power, and Simple Machines

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valef1222  on May 18, 2012

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# Final Exam Chapter 14: Work, Power, and Simple Machines

 workthe product of force and distance is done when a force acts on an object in the direction the object moves
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#### Definitions

work the product of force and distance
is done when a force acts on an object in the direction the object moves
joule SI unit for work
when a force of 1 newton moves an object 1 meter in the direction of the force, 1 _____ of work is done
power the rate of doing work
SI unit is watt or horsepower
machine a device that changes a force
make work easier to do
What machines change change the size of force needed, the direction of a force, or the distance over which a force acts
input force force you exert on a machine
output force force that is exerted by a machine
input distance the distance the input force acts through
output distance the distance the output force is exerted through
input work the work done by the input force acting through the input distance
output work the output force multiplied by the output distance
mechanical advantage the number of times that a machine increases an input force
actual mechanical advantage the ratio of the output force to the input force
=output force/input force
the ratio of the input distance to the output distance
efficiency the percentage of the work input that becomes work output
always less than 100%
simple machines lever, wheel and axle, inclined plane, wedge, screw, and pulley
lever a rigid bar that is free to move around a fixed point
1st class lever fulcrum is between input force an output force
mechanical advantage: 1, >1, and <1
exs. seesaw, bottle opener, crow bar, balance
2nd class lever fulcrum, then output force, then input force
mechanical advantage: always less than 1
exs. wheelbarrow, nutcracker
3rd class lever fulcrum, then input force, then output force
mechanical advantage: always greater than 1
exs. baseball bat, golf club, sword
fulcrum the fixed point the bar rotates around on a lever
wheel and axle simple machine that consists of 2 disks or cylinders.
IMA: divide radius where the input force is exerted by the radius where the output force is exerted
pulley simple machine that consists of a rope that fits into a groove in a wheel
IMA: equal to the number of rope sections supporting the load being lifted
fixed pulley a pulley with a wheel attached in a fixed location.
the direction of the exerted force is changed but the size of force stays the same
IMA: always 1
moveable pulley pulley attached to the object being moved rather than to a fixed location
pulley system combining fixed and moveable pulleys to achieve a larger mechanical advantage
inclined plane slanted surface along which a force moves an object to a different elevation
IMA: equals the distance along the inclined plane divided by its change in height
wedge v-shaped object whose sides are two inclined planes sloped toward each other
IMA: a thin wedge of a given length has a greater IMA than a thick wedge of the same length
screw is an inclined plane wrapped around a cylinder
IMA: greater IMA are screws with threads that are closer together
compound machine a combination of two or more simple machines that operate together
exs. car, washing machine, clock

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