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Simple Machines

Give me a lever long enough, and a fulcrum on which to place it, and I will move the world.

Aristole

Definitions to know :

Work - occurs when a force moves an object over a distance; it is the amount of energy transferred by a force to a moving object
Energy - ability to cause change; can change the speed, direction, shape, or temperature of an object
Simple machines are used to make work easier by

Transferring a force from one place to another,
Changing the direction of a force,
Increasing the magnitude of a force, or
Increasing the distance or speed of a force.
Provide a mechanical advantage
- The advantage created by a machine that enables people to do work while using less force
- Ratio of resistance force to effort force in a machine

Load - the weight being lifted by the simple machine. Also called resistance , resistance load , load force , resistance force , output force
Effort - effort is the force placed on the simple machine to move the load. Also called applied force , effort force or input force
Mechanical Advantage - the advantage created by a machine that enables people to do work while using less force

What are simple machines?

. Simple machines are tools that make work easier

. They have few or no moving parts

. These machines use energy to work

. Do work with one movement

. Make our work easier by letting us use less mechanical effort to move an object

. Simple machines make work easier for us by allowing us to push or pull over increased distances

. Use the idea of spreading force over distance: if you push further , you can use less force

. You are doing the same amount of work - it just seems easier

. You move an object a greater distance to accomplish the same amount of work.

. There's a trade-off of energy when using simple machines.

. Simple machines give us an advantage by changing the amount, speed, or direction of forces

. They allow us to use a smaller force to overcome a larger force

. The amount of effort saved when using machines is called mechanical advantage or MA

What are Compound or Complex Machines?

. Two or more simple machines working together

. Most of the machines we use today are compound machines

Types of Simple Machines

. Two groups:

. Inclined planes

. Ramp

. Wedge

. Screw

. Levers

. Lever

. Wheel & Axle

. Pulley

Ramp or Inclined Plane

. Both terms are used

. A flat surface that is higher on one end - slanting surface connecting a lower level to a higher level.

. You can use this machine to move an object to a lower or higher place.

. Inclined planes make the work of moving things easier - allows us to raise an object with less effort than if we lifted it directly upward.

. You would need less energy and force to move objects with an inclined plane.

. Trade-off : The way an inclined plane works is that to save effort, you must move things a greater distance

. The longer the distance of the ramp, the easier it is to do the work

. It will take a much longer time to do the work

. The shallower the ramp, the easier it is to move the object

. The trade-off is that you must move the object farther to lift it to the same height

Examples of Inclined Planes :

. Ramp

. Slanted Road

. Path up a Hill

. Slide

Wedge

. A wedge is a simple machine used to push two objects apart

. A wedge is usually made up of two inclined planes

. These planes meet and form a sharp edge. This edge can split or push objects apart

. A wedge is an inclined plane which moves

. A wedge can also be used as a lifting device, by forcing it under an object

. Most wedges (but not all) are combinations of two inclined planes.

. Can also be round, like the tip of a nail

. The narrower the wedge (or the sharper the point of a wedge), the easier it is drive it in and push things apart

. Trade-off : To split something apart really wide, you have to push the wedge a long distance.

. Generally it can be anything that splits, cuts, or divides another object including air and water

Examples of Wedges :

. Knife

. Axe

. Teeth

. Forks

. Nails

Screw

. An inclined plane that winds around itself

. a wedge at the tip

. A screw has ridges and is not smooth like a nail

. Some screws are used to lower and raise things

. They are also used to hold objects together

. A screw is like the ramp -the width of the thread is like the angle of an inclined plane

. The wider the thread of a screw, the harder it is to turn it.

. Trade-off : The distance between the threads depends on the slope of the inclined plane - the steeper the slope, the wider the thread

. Screws with less distance between the threads are easier to turn

Examples of Screws :

. Jar Lids

. Light Bulbs

. Stools

. Clamps

. Jacks

. Wrenches

. Spiral Staircase

Lever

. A lever is a board or bar that rests on a turning point

. This turning point is called the fulcrum

. An object that a lever moves is called the load

. The load is a force or object which must be overcome by the lever

. The applied force or effort or input force is the force you use to move the lever

. Lifts or moves loads

. By changing the position of the fulcrum, you can gain extra power with less effort

. The closer the object is to the fulcrum, the easier it is to move

. Most common simple machine because just about anything that has a handle on it has a lever attached

. The arm length of the lever is determined by the position of the fulcrum

. Used to transfer force

. It can be used to increase the force that is applied, or make something move in a different direction, or through a greater distance

. It can be used to lift something that is far away

. It is the same principle as the inclined plane - the greater the distance over which the force must be applied, the smaller the force required to do the work (lift the load)

. Force moves over a longer distance

. Depending on where the fulcrum is located

. A lever can multiply either the force applied or

. The distance over which the force is applied

Three types of levers:

. 1 st class

. 2 nd class

. 3 rd class

1 st Class Levers

. Fulcrum in the center - between load & effort

. The lever changes the direction of force

. The fulcrum is placed close to the load , and this will let you move the load with just a small applied force (effort)

. This type of lever system gives you a mechanical advantage , which means that the force you apply gets multiplied , so you can put a large force on the load.

. The trade-off of using a lever like this is that you have to apply a force over a large distance , and the load itself will move only a short distance

. The fulcrum is between the load and where you apply the force (effort)

. This lever system has no mechanical advantage.

. Whatever force is necessary to move the load is the force you must apply

. This type of lever system takes advantage of another property of some levers: they reverse the direction of the force

. You can push in one direction, and the load moves the other way

. The fulcrum is nearer the applied force (effort)

. Much more force than the force of the load itself must be applied

. If you're lifting something, it will require much more force than would be needed if you were to just lift the load by yourself - this type lever system makes the work harder !!

. This type of lever system usually uses a motor to lift the load

. The load is far away , and it moves a long distance

. We get a small movement where we applied the force

Examples of 1 st Class Levers:

. See-saw

. Scissors

. Pliers

2 nd Class Levers

. The load is in the center - between the fulcrum and the applied force or effort

. Causes the load to move in the same direction as the force you apply

. When the load is nearer to the fulcrum, the effort needed to lift the load will be less

. If you want to move a very large load with a small effort, you must put the load very close to the fulcrum

Examples of 2 nd Class Levers:

. Wheelbarrow

. Nutcracker

3 rd Class Levers

. The applied force or effort is in the center - between the load and fulcrum

. This lever system does not give any mechanical advantage

. No matter where you apply the force, the force you apply must always be greater than the force of a load

. No matter how close or how far the load is from the fulcrum, the effort used to lift the load, has to be greater than the load!

. The load moves in the same direction as the force you apply

. A motor is usually used with this lever system to lift loads at a distance

. Speeds up movement

Examples of Third Class Levers:

. Your bent arm

. Fishing rod

Wheel & Axle

. A wheel with a rod, called an axle, through its center lifts or moves loads

. The axle is a rod that goes through the wheel

. This lets the wheel turn

. The wheel & axle can be used as a tool to multiply the force you apply

. Or to multiply the distance traveled

. A lever that is able to rotate through a complete circle (360° )

. The circle turned by the wheel is much larger than the circle turned by the axle.

. The increased distance over which the force is applied as the wheel turns results in a more powerful force on the axle, which moves a shorter distance

. Trade-off-: The larger the diameter of the wheel, the less effort you need to turn it, but you have to move the wheel a greater distance to get the same work done.

Examples of Wheels and Axles:

. Cars

. Roller skates

. Door knobs

. Gears

Pulleys

. Instead of an axle, the wheel could also rotate a rope or cord. This variation of the wheel and axle is the pulley

. In a pulley, a cord wraps around a wheel

. As the wheel rotates, the cord moves in either direction

. When a hook is attached to the rope you can use the wheel's rotation to raise and lower objects.

. The rope fits on the groove of the wheel

. One part of the rope is attached to the load

. When you pull on one side of the pulley, the wheel turns and the load will move

. Pulleys let you move loads up, down, or sideways

. Pulleys are good for moving objects to hard to reach places

. A pulley makes work seem easier because it changes the direction of motion to work with gravity

. A pulley saves the most effort when you have more than one pulley working together

. Trade-off - as you increase the number of pulleys, you also increase the distance you have to pull the rope

. In other words, if you use two pulleys, it takes half the effort to lift something, but you have to pull the rope twice as far

. Three pulleys will result in one-third the effort - but the distance you have to pull the rope is tripled!

Types of Pulleys:

. Fixed pulleys

. Movable pulleys

. Single Pulleys

. Combination pulleys

Single Pulleys

. A single pulley reverses the direction of a force

. With one pulley, the force you must pull with is the same as the weight of the object .

. In order to raise the object a height of 1 meter, you must pull the rope 1 meter

. Trade-off : the end of the rope must move a greater distance than the load

Combination Pulley

. Two or more pulleys connected together

. Allow a heavy load to be lifted with less force

. Effort needed to lift the load is less than half the weight of the load

. The main advantage of this pulley is that the amount of effort is less than half of the load

. Trade-off - you need more rope and you need to pull more rope!

Fixed Pulleys

. May be single or combination

. Doesn't change position

. Makes work easier by changing the direction of the applied force

. The force required to lift the load remains the same as lifting it without the pulley

. But it is much easier it is to raise a flag from the ground, instead of climbing up the pole

. If a force needs to be applied around a corner, a pulley allows us to overcome friction

. The only pulley that when used individually, uses more effort than the load to lift the load from the ground

. The fixed pulley is attached to an unmovable object like a ceiling or wall

. Acts like a first class lever with the fulcrum being located at the axis

. The bar or lever arm becomes a rope

. The advantage of the fixed pulley is that you do not have to pull or push the pulley up and down.

. The trade-off is that you have to apply more effort than the load

Movable Pulleys

. May be single or combination

. A pulley that moves with the load ( both the load and the pulley move)

. The load moves in the same direction as the applied force

. The movable pulley allows the effort to be less than the weight of the load

. It takes less force to raise an object than if you used only your hands

. The amount of force required depends on the number of supporting ropes

. The greater the number of pulleys and supporting ropes, the smaller the force required.

. Trade-off : the less force required, the greater the distance the rope must be pulled further than the load actually moves

. The movable pulley acts as a second class lever

. The load is between the fulcrum and the effort

. The main advantage of a movable pulley is that you use less effort to pull the load

Examples of Pulleys:

. Flag Poles

. Sailboat

. Blinds

. Crane

Sources for graphics:

http://www.edinformatics.com/math_science/simple_machines/

http://pages.cthome.net/CAPThome/PG1MEASU.html