| Intermediate Technology Education | Control Technology | Pre-Design | Topic 3 | Activity 4 |
Mechanical Systems
Simple machines are the basic machines defined by science. They are the lever, inclined plane, wheel and axle, wedge, pulley and the screw. Simple machines are used to gain mechanical advantage. That is, the force required to move a load can be less that weight of the load. In exchange you have to apply the force over a greater distance than the vertical motion of the load.
Levers are a class of simple machine used to move loads with different amounts of force, depending on the location of the fulcrum. There are 3 types (classes) of lever. In the figures below, D1 is the distance from the fulcrum to the load, and D2 is the distance from the fulcrum to the force required to move it.
In the case of the class 3 lever, can the force ever be less than the load?
Here are simple examples of levers
By moving the fulcrum, you can control the amount you can lift with the same effort. The three classes are demonstrated in the following video clip
Video Levers
An inclined plane is simply a sloped surface. A load can be slid along the inclined plane to move it a vertical distance. By adjusting the slope of the plane, you can control how much force it takes to move the load. The lower the slope, the less force is required, but the longer the distance it has to be moved to get the same vertical rise.
The picture below illustrates one use of an inclined plane.
The wheel and axle appear in all sorts of equipment, from toys to industrial machines. The load may be at the axle or at the rim of the wheel. Which one requires less force than the load?
The wedge is essentially a pair of inclined planes. It moves a load that is at right angles to the force
The wedge has many uses, especially for cutting tools. All knives, saws, planes and chisels use the wedge for cutting. A few are illustrated below.
Pulleys are essentially wheels with hollowed out rims.
Pulleys are freewheeling on their axles. Mechanical advantage is only obtained if they are combined in multiples in a block, with two blocks of pulleys used. In the figure below, you can see the progression from pulleys to block to two blocks. This configuration can produce large mechanical advantages.
The screw is an inclined plane wrapped around a cylinder.
Mechanisms are devices made from combinations of simple machines. A few examples of geared mechanisms follow. Gears are essentially wheels with teeth. The teeth give a positive lock from one gear to another and prevent slipping.
Here are a few small tools that are based on simple machines. Can you identify all the simple machines employed in each mechanism?
Mechanical control mechanisms are used to start and stop, open and close, regulate speed and so on. For example
Video Pulleys
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