## Greco 6th: Machines

##### Created by:

MrGreco  on May 9, 2012

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# Greco 6th: Machines

 Define work.Work means using force (pushing or pulling) in order to move an object a certain distance.
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#### Definitions

Define work. Work means using force (pushing or pulling) in order to move an object a certain distance.
Work Formula: Work = force x distance
W = f x d
Mr. Moore pushes a box with a force of 500 Newtons over a distance of 2 meters. How much work was done? The force is 500 Newtons and the distance is 2 meters and we are looking for how much work was done. Therefore:

W = f x d
W = 500 N x 2 m

W = 1000 N/m

W = 1000 Joules
What is a machine? A machine is any device that helps make work easier.
What is the difference between a simple and a compound machine? A simple machine is a tool made of one or two parts and a compound machine contains two or more simple machines.
Identify the following as a simple or a compound machine:

car, nail clippers, airplane, chopsticks
car = compound machine

nail clippers = simple machine

airplane = compound machine

chopsticks = simple machine
A lever is made of... one or more bars resting on a support. The support is called the fulcrum. Levers apply an effort force to a load.
Levers can change the... amount of force or the direction of the force.
Difference between the 3 classes of levers: The difference between the 3 classes of levers is the location of the effort force, fulcrum, and load.
Some examples of levers: Seesaw and pliers are first class levers.

Nutcracker and wheelbarrow are 2nd class levers.

Chopsticks and a crab's claw are 3rd class levers.
An inclined plane is a... straight slanted surface. A example is a ramp.
Why are inclined planes helpful? An inclined plane or ramp makes moving a load from a low place to a higher place easier. Moving the load up a ramp takes less force than lifting it straight up but the load travels a greater distance. In both cases, you do the same amount of work.
A wedge is... one or two inclined planes that move. The slanted edges of the inclined planes come to a point.
How does a wedge do work? To do it work, a wedge must be moving like a knife or ax. A force directed at the flat end of the wedge drives the point forward. The inclined planes of the wedge change the direction of the force.
What is a screw? A screw is an inclined plane wrapped in a spiral around a cylinder. The ridges of the screw are called threads. If you could unwind the threads, you would see they form an inclined plane.
Why are screws important simple machines? When turned, a small force is applied over a long distance along the inclined plane. The screw applies large force through a short distance when it is pushed. Screws are often used as fasteners. Examples are jar lids and light bulbs.
What is a wheel and axle? It is a wheel with a rod that goes through the wheel's center. The diameter of the wheel is much larger than the diameter of the axle. Examples are water faucets, ferris wheels, and door knobs.
How does a wheel and axle work? The wheel turns through a much greater distance than the axle. But the smaller turn of the axle is much more powerful. A wheel and axle can increase a force or increase the distance through which a force acts.
What is a pulley? A pulley is a grooved wheel with a rope, chain, or belt around it. A load is attached to one end of the rope and the effort force is applied to the other end.
What is the difference between a fixed and a movable pulley? A fixed pulley doesn't move, it changes the direction of the force. A movable pulley moves with the object. Movable pulleys decrease the amount of force you must apply, but the force you apply occurs over a greater distance.
How does a flagpole work? A flagpole is a fixed pulley. There is no change in force however, there is a change in direction because as you pull a flag pole rope down the flag goes up.
What is a block and tackle? A block and tackle uses a fixed pulley and a movable pulley together. A block and tackle with a lot of pulleys could help lift a very heavy load, like a piano.
Does using a machine change how much work is done? No, the amount of work is the same however, the amount of force or distance changes.

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