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Simple Machines is an event that was last held in the 2008 season.
Simple Machines is an event that requires participants to calculate the IMA (ideal mechanical advantage) and AMA (actual mechianical advantage) of simple machines, as well as efficiency in some cases. This event is generally run as stations. For the 2008 season, the machines used were a lever, inclined plane, pulley system, and a wheel and axle.
A simple machine is a mechanical device for applying force. They are useful because they can make physical jobs easier, by changing the magnitude or direction of the force.
IMA and AMA
When discussing simple machines, it is important to understand the concept of mechanical advantage.
IMA stands for Ideal Mechanical Advantage.
Ideal Mechanical Advantage is the number of times a machine multiplies an effort force. For example, if a machine has an IMA of 2, that means that the force applied was doubled by the machine. If the IMA of a machine is 1/2, that means that the force applied was halved by the machine. If the IMA is 1, that means the force applied stayed the same.
However, machines with a high IMA are not always desirable. The higher IMA a machine has, the less distance it moves the output based on the input force. If a machine has an IMA of greater than 1, then it is moving the object less of a distance than it would have. A machine with an IMA less than one will move an object a further distance, at the sacrifice of force.
This balance between force and distance can be written in the following formula:
W = f x d
Where Work (SI unit Joule) equals the force on the output multiplied by the distance the output moved.
AMA stands for Actual Mechanical Advantage. It takes into account things like friction and drag. AMA will not be used in scoring in Mission Possible.
Types of Simple Machines
There are six types of simple machines.
A simple pulley is a string looped around a fixed axle. If a load is attached to one end of the string, you could pull it up, but would require the same amount of force to pull the load over the pulley as it would if you had no pulley. You could balance it by putting an equal load on the other side. Take a look at this diagram:
Pulleys can be more useful than that when there is more than one pulley wheel to a pulley system. If the load's weight is spread between two strings, there is an IMA of 2. Here is an example of a pulley system using two pulley wheels, with an IMA of 2:
Imagine that you are pulling on the string with the little arrow. If you pulled it 2 feet downwards, the hook will rise 1 foot. This is because there are two strings that lift the hook and only one string that is being pulled. This means that you can lift a heavy load as if it were only half as heavy. Now, imagine if three strings were attached to the hook. The IMA would now be 3. But remember only count the supporting lines, or the lines that are being pulled up. In the diagram, the line with an arrow is being pulled down, so it is not counted in the IMA.
In conclusion, the easy way to tell what the IMA of your pulley system is to count the number of pulley wheels.
Pulleys are easily acquirable at your local hardware store. To make the circular part of the pulley, you could also use wheels from Lego sets (without the tires, of course).
"Inclined plane" is just a fancy word for a ramp. To find the IMA of an inclined plane, divide the diagonal length of the ramp by the vertical length of the ramp.
The IMA of this ramp is 60/5=12. Since the circular weight (the one being lifted) is less than 12 times heavier than the square weight, the square weight is able to lift the circular weight. (The picture is not to scale)
Wheel and Axles
A wheel and axle system can be used in many ways: to transport something, to turn something else on the axle, or to turn another wheel and axle.
This diagram shows how to find the IMA of a wheel and axle simple machine. Basically, the IMA of a wheel and axle is the radius of the wheel divided by the radius of the axle.
A lever is, in basic terms, a rigid bar resting on a pivot point, or the fulcrum. To work the lever, effort must be applied to move the load, which is usually opposite the effort, across the fulcrum. There are three types of levers.
- First Class
- The fulcrum is in the middle, the effort is on one side, and the load is on the other. An example of a first class lever would be a seesaw or a crowbar.
- Second Class
- The fulcrum is to one side, the load is in the middle, and the effort is on the other side. An example of a second class lever would be a wheelbarrow.
- Third Class
- The fulcrum is to one side, the load is on the other side, and the effort is in the middle. An example of a third class lever would be tweezers or your elbow.
To find the IMA of a lever, divide the distance between the fulcrum and the effort by the distance between the fulcrum and the load. Therefore, if the fulcrum is moved closer to the load, the easier it is going to be to lift a load, and the higher the IMA is.
A wedge is a simple machine that separates two objects by converting downward force to sideways force. Imagine a triangular block of wood and two adjacent bouncy balls. If you put the triangular block between the two bouncy balls and pushed down, it would separate the two bouncy balls. The IMA of a wedge is how far the wedge went down divided by the distance it separated the two objects.
Screws convert rotational force to vertical force. A screw is essentially inclined plane wrapped around a central axis. An example would be a drill or a screw for construction. The formula for IMA is 2(pi)L/p, where L is the length of the handle and p is the distance between adjacent screw threads.