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Types of Simple Machines

Science, Grade 6

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Table Of Contents: Types of Simple Machines

1. Types of Simple Machines
There are several types of simple machines, including an inclined plane, a wedge, a screw, a lever, a wheel and axle and a pulley. All of these machines make work easier for us.
2. Inclined Plane
An inclined plane is a straight, sloped surface that increases the distance over which the input force is applied. This simple machine reduces the amount of input force needed to perform work. Examples of inclined planes include ramps, slides and staircases. The mechanical advantage of an inclined plane is equal to the length of the incline divided by the height of the incline.
3. Wedge
A wedge is a moving inclined plane that increases the distance over which the input force is applied. This type of simple machine reduces the amount of input force needed to perform work. An axe, a knife and a shovel are all examples of wedges. The mechanical advantage of a wedge is calculated by dividing the length of the wedge by its greatest width. Mechanical advantage increases as the wedge becomes longer and thinner.
4. Screw
A screw is an inclined plane that is wrapped around a cylinder. It increases the distance over which the input force is applied, reducing the amount of input force needed. If you think about turning a screw, it is fairly easy to turn, but you have to turn it many times. Other examples of screws include a screw lid jar, a drill bit and a light bulb. Threads that are close together increase the mechanical advantage of a screw.
5. Lever
A lever is a bar or board that pivots around a fixed point called a fulcrum. Seesaws, bottle openers, wheelbarrows and hockey sticks are all examples of levers. The mechanical advantage of a lever is calculated by dividing the distance from the fulcrum to the input force by the distance from the fulcrum to the output force.
6. Classes of Levers
There are three classes of levers, depending on where the fulcrum is located. In a first-class lever, like a seesaw, the fulcrum is located between the input and output force. The direction of the input force is opposite to the output force. In a second-class lever, like a wheelbarrow, the output force is between the fulcrum and the input force. The direction of the input force does not change, but as the force is applied over a distance, the output force is increased. In a third-class lever, like a hockey stick, the input force is between the fulcrum and the output force. The direction of the input force does not change, but the distance of the output force is increased.
7. Wheel and Axle
A wheel and axle is a simple machine made up of one large cylinder, the wheel, attached to a smaller cylinder, the axle. If the input force is applied to the axle which has a smaller diameter, then the output force is spread over a greater distance on the wheel which has a larger diameter. Examples include a vehicle wheel, a rolling pin and a doorknob. The mechanical advantage of a wheel and axle is calculated by dividing the radius of the wheel by the radius of the axle.
8. Pulley
A pulley is a type of simple machine that consists of a cable placed around a grooved wheel. A simple, fixed pulley changes the direction of the input force, making the work easier. Movable pulleys and pulley systems require less input force applied over a longer distance in order to increase the output force. Pulleys are used in many ways and can be found on flagpoles, window blinds and boat sails.
9. Types of Pulleys
A pulley can be fixed or movable. A fixed pulley, such as the one found at the top of a flagpole, is attached to a structure. Fixed pulleys have a mechanical advantage of 1. A movable pulley moves along with the load that is being carried. It has a mechanical advantage of 2. A block and tackle pulley system combines a fixed and movable pulley. This type of system can often be found on cranes. The mechanical advantage of this block and tackle is 4.
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