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# 7Sci Chapter 20

### Work & Machines

What is a device that makes work easier by changing the size or direction of force? machine
What is the work done by a machine on an object? output force
What is the work that you do on a machine? input force
What is the number of times the machine multiplies force? mechanical advantage
What is a comparison of a machine's work output with the work input? mechanical efficiency
What equation would you use to find mechanical advantage? MA=output force/input force
What causes machines not to be 100% efficient? friction
What is a example of a person doing work on an object? a crossing guard raising a stop sign that weighs 10N
What simple machine was used by the Egyptians to build pyramids? inclined planes and levers
If a barbell weighs 160N, what other information do you need to calculate how much work it takes to life it? how high the barbell is being lifted
What machine always has a mechanical advantage of less than 1? a poorly lubricated, movable pulley
What does a fixed pulley change? the direction of a force
When a machine increases the size of the force exerted, what happens to the distance? it must increase
What type of simple machine is a screw? wheel and axle
What is it called when a force causes an object to move in the direction of the force? work
What is the rate at which power is transferred? energy
What do you call the number of times a machine multiplies force? mechanical advantage
What is a machine that is made of two simple machines? compound machine
What is machine with a grooved wheel that holds a cable? pulley
A moving object has what kind of energy? kinetic
How does a ramp make lifting a heavy object easier? less force is needed to move the object over a longer distance
Where is the input force of a wheel and axle exerted? a circular distance
What is an example of a compound machine? block and tackle pulley
What two things must happen for work to be done? the object must move in the same direction as the force
What is a doorknob an example of? wheel and axle
What type of lever places the load between the input force and the fulcrum? a 2nd class lever
What type of pulley is attached to something so it does not move? a fixed pulley
What is a bar that pivots on a fulcrum called? a lever
What is the SI unit equivalent to 1 Newton-meter called? joule
What is a machine that has 100% mechanical efficiency? an ideal machine
What is F x d used for? to calculate work
What is kinetic energy? a moving object that has this type of energy
What is power? the rate at which energy is transferred
What is a watt? the unit used to express power
What is W รท t used for? to calculate power
What is a first class lever? a lever where the fulcrum is between the input force and the load
What is a second class lever? a lever where the load is between the input force and the fulcrum
What is a third class lever? a lever where the input force is between the fulcrum and the load
Created by: ndmsteach