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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.

Aristotle

Definitions to know :

• Work - done when an applied force causes an object to move in the direction of the force
• Energy - ability to cause change; can change the speed, direction, shape, or temperature of an object
• 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