From EngQuest 2010
Have you checked out the Simple Machines Animation yet? Did you have your speakers turned on? Cool isn't it?
Here you will discover all sorts of awesome things about simple machines and how they work. There are some great diagrams too!
A machine is something that makes it easier for us to do work, such as moving objects. This happens when a force (a push or a pull effort) makes something (a mass or load) move for a distance. Simple machines are ones which have only one part to do the work. One example of a simple machine is a lever (see Diagram 1). The force applied to the lever (the crowbar) makes the rock move and the work easier to do.
More complicated machines (sometimes called Compound Machines) are made up of a number of simple machines that work together to help do the work. A wheelbarrow is one example of a compound machine. It has two levers (the handles) to help lift the load, and a wheel and axle to make it easier to move the load forward (see Diagram 2).
Load, effort and mechanical advantage
These are terms that are used to describe how simple machines work.
The load is the object that is moved. In Diagram 1, the load is the weight of the rock.
The effort is the force that is used to do the work. In Diagram 1, the effort is the force that the person applies to the crowbar to move the rock.
You can use a simple machine to move a large load with a smaller effort than you would need if you did not have a machine to help you. This is called gaining a mechanical advantage. If the rock in Diagram 1 weighed 100 kilograms, the lever might allow you to move it with a force of only 25 kilograms. The load would then be 4 times as big as the effort you applied, giving you a mechanical advantage of 4 (load divided by effort).
Types of simple machines
There are a number of different types of simple machines. These include:
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Compound machines are made up of a combination of these simple machines. Can you identify all the simple machines in the Simple Machines Animation?
Inclined planes
An inclined plane is a flat surface that is at an angle to the load. This type of 'machine' has no parts that move.
An example of an inclined plane is a ramp for wheelchairs (see Diagram 3). The inclined plane of the ramp makes it easier for the person in the wheelchair to move up into a building. The load (the weight of the person in the wheelchair) can be moved up the ramp into the building against the force of gravity using a smaller effort (or force) than would be required to lift the person and the wheelchair the same height.
For example, the ramp needed to raise the wheelchair 1 metre higher might be 10 metres long, so the wheelchair needs to move 10 metres up the ramp in order to raise its height by 1 metre. In trading force for distance, the force pushing it up the slope needs to happen for 10 times the distance that the person in the wheelchair is raised. This gives a mechanical advantage of 10 (the distance travelled divided by the height gained).
The steeper the slope of the inclined plane, the more effort it takes to move the person in the wheelchair up the slope. The steeper slope in Diagram 3 is only 5 metres long. This gives the person in the wheelchair a mechanical advantage of only 5 and it therefore requires twice the effort to climb the same height.
Some other examples of inclined planes include roads leading up slopes, car ramps in parking stations, and even staircases for people to walk up and down. You will agree that it is easier to walk up a ramp or a staircase than to climb to the same height up a ladder.
Likewise, inclined planes can be used to work with gravity as objects roll down them. Did you notice how the inclined planes work with gravity to make the compound machine operate in the Simple Machines Animation? How many examples of inclined planes did you find?
Levers
A lever is a rigid bar that rotates around a fixed point. This balancing point is called the fulcrum. A lever uses a force (or effort) to make the load move.
There are different types of levers, depending on where the load, the effort, and the fulcrum are positioned. For this reason, levers are classified into 3 separate groups: Class 1, Class 2, and Class 3.
- Class 1 lever: This is where the fulcrum is between the load and the effort.
One example would be using a screwdriver to open a can of paint (see Diagram 4). In this case, the screwdriver is the lever. The load is the resistance of the lid of the paint can, the effort is the force that the person applies to the lever, and the fulcrum is the outside rim of the paint can that helps you to lever up the lid.
Imagine how much harder it would be if you had to lift the lid off a paint can with your fingers, without the help of a lever! The screwdriver provides a mechanical advantage (a smaller force is being used to overcome a larger load).
The direction of the force is also being changed by the lever. Pushing down on the lever (the screwdriver) raises the load (the paint can lid).
Other examples of Class 1 levers include using a bottle opener to open a bottle of drink, using a claw hammer to pull out a nail, and playing on a see-saw.
- Class 2 lever: This is where the fulcrum is at one end of the lever, the effort is at the other end, and the load is in between.
One example would be a person lifting a load in a wheelbarrow (see Diagram 5). In this case, the wheelbarrow and its handles are the lever, the load is the weight in the wheelbarrow, and the force applied by the person lifting the handles is the effort. The fulcrum (the balance point of the lever) is the axle of the wheelbarrow.
The mechanical advantage (remember, this is what makes the load easier to lift) is created by having the load closer to the wheelbarrow axle (the fulcrum) than to the person lifting the handles (the effort).
Other examples of Class 2 levers are staplers that staple sheets of paper together, and nutcrackers that have the hinge at the end of the machine.
- Class 3 lever: This is where the fulcrum is at one end of the lever, the load is at the other end, and the effort is in between. These levers involve using a large effort to move a small load a long distance.
An example is a person playing golf (see Diagram 6). In this case the golf club plus the person's arms is the lever, the golfer's shoulder is the fulcrum, the force being applied to the golf club by the golfer's hands is the effort, and the load is the weight of the golf ball.
The aim is to use a large force for a small distance (the effort applied to the golf club by the golfer's hands) to move a small load (the golf ball) for a much larger distance.
This type of lever often trades distance for force. You can use a large force for a small distance to move a small load for a larger distance.
Other examples are using a cricket bat, a tennis racquet or a hockey stick to hit a ball, and a fishing rod to cast a fishing line.
There are many levers in the Simple Machines Animation. How many can you spot?
Levers in balance
For a lever to be in balance (not moving) the forces trying to turn it in one direction (the turning effect) will be exactly balanced by the forces trying to turn it in the opposite direction.
A see-saw is actually a lever with a fulcrum in the middle (see Diagram 7). Think about a see-saw that is balanced, with two people sitting at different distances from the fulcrum. If one person is twice as heavy as the other, the lighter person must sit twice as far away from the fulcrum as the heavier person for the see-saw to be balanced.
This is because the turning effect depends on two things - the size of the force (in this case the weight of the people), and the distance from the fulcrum. Longer levers give more leverage than shorter ones. Therefore, the smaller person has to create greater leverage to balance the heavier weight of the other person by sitting further away from the fulcrum. Once balanced, it requires very little force for each person to push the see-saw up and down with their legs.
Wheels and axles
A wheel and axle is a simple machine that is made up of a smaller cylinder (the axle) joined to a larger cylinder (the wheel). To work efficiently together, the axle must be connected to the wheel in such a way that it allows the wheel to rotate evenly about its centre.
Often a wheel and axle is used to reduce friction and to make it much easier to move a load. An example of this is a trolley, or any other wheeled vehicle (see Diagram 8). You will agree that it would be much easier to move a heavy load with a trolley that has wheels than to push the same trolley across the ground with no wheels.
There are two examples of wheels and axles in the Simple Machines Animation. Did you notice how they are both used with inclined planes to create motion?
Pulleys
A pulley consists of a rope (or a belt or a chain) that passes around a wheel. Sometimes the pulley is fixed, and sometimes it moves with the object that is being shifted.
Fixed pulleys
Fixed pulleys are used to change the direction of a force. An example would be a pulley at the top of a flagpole (see Diagram 9). Because of the pulley at the top, the person raising the flag can stand on the ground and hoist the flag by pulling down on the rope. Imagine how much harder it would be without a pulley - the person would need to climb up the flagpole with the flag!
Fixed pulleys do not give a mechanical advantage. The distance that the load moves is exactly the same as the distance moved by the effort.
Other examples of fixed pulleys include:
- the pulley at the top of a yacht mast. The deckhand can raise the sail up the mast by pulling down on the rope. The pulley has changed the direction of the force to make it much more convenient.
- the pulley at the end of the boom of a crane. The crane works by pulling upwards to lift the load. The pulley changes the direction of the force so that the motor that does the lifting can be on the ground rather than at the top of the crane.
Did you spot the two pulley examples in the Simple Machines Animation? How are they different?
Moving pulleys
Diagram 10 shows one moving pulley attached to the engine (the load), and one fixed pulley attached to the support above. This type of pulley system is called a 'block and tackle', where 'block' refers to the pulleys and 'tackle' is the chain that the person is pulling to lift the engine.
The fixed pulley changes the direction of the force to make it more convenient. This means that the person can lift the load by pulling down on the rope. The moving pulley gives a mechanical advantage and makes it easier to lift the load.
In a pulley system, each moving pulley halves the effort, but means that the effort has to be applied for twice the distance. This is why a person can lift an engine out of a car using only a 'block and tackle'. The mechanical advantage is achieved by pulling the chain over a much longer distance than the distance that the engine is actually lifted.
Wedges
A wedge is made up of two inclined planes joined together at an angle. A good example of a wedge is an axe, where the head of the axe is made up of two inclined planes which do the work.
Think about an axe being used to chop and split a piece of firewood (see Diagram 11). The axe is actually being used to change the direction of the force. The force of the axe blow is downwards, but the wedge changes this downward force into two sideways forces, causing the wood to split apart.
Other examples of wedges include:
- a knife blade
- a chisel used in woodworking
- the point at the end of a nail
- a doorstop that is wedged under a door to prevent it from moving.
Did you spot the wedge used in the Simple Machines Animation? How was it used?
Screws
A screw is really an inclined plane that is coiled around a shaft (see Diagram 12).
The inclined plane of the screw makes the work easier by allowing the effort to be applied over a longer distance. This is another example of trading force for distance. The closer together the threads of the screw are, the greater the mechanical advantage.
Some examples of screws include:
- wood screws
- the screw in a car jack
- the screw on the lid of a jar
- the blades of a fan
- the blades of an aeroplane propeller.
Did you notice the screw in the Simple Machines Animation? How was it used?
Gears
Gears are toothed wheels that fit together so that when one gear turns it also turns the other gear. Sometimes the gears fit directly together, and sometimes they work together through a chain or a belt (see Diagram 13).
Gears can produce either a gain in distance or a gain in force, depending on how they are used. This effect depends on the ratio of the number of teeth in the two gears working together.
Observe the animated gears. The big one has 40 teeth, and the small one has 20 teeth. Suppose that the big gear is being used to drive the small gear. Each time the big gear rotates once, it uses all its 40 teeth. The small gear has only 20 teeth, so it is rotated twice. This is producing a gain in distance.
On the other hand, suppose that the small gear is being used to drive the big gear. In this case, the small gear will need to rotate twice in order to turn the big gear around once. This is producing a gain in force.
Click on the gears to see them work.
Some examples of the use of gears include:
- mechanical clocks
- car gearbox and drive systems
- electric drills
- VCR, CD and DVD players.
Did you notice how gears were used in the Simple Machines Animation? How many examples could you find?
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