Incline Your Mind - Simple Machine Resources for Kids!
A simple machine is one in which that can change the amount or direction of a force. They are considered simple because they used the simplest mechanism to provide this change of leverage of the force. Technically there are six classical simple machines that were defined by scientists during the renaissance period. These machines include the inclined plane, lever, wedge, wheel and axle, screw and pulley. These six simple machines can be further separated into two groups; those that use vectors to alter the force along a line and those that use torque to change the force around a pivot point. The simple machine will contain devices and mechanisms to change the force. These simple machines are used to create more complicated machines and most machines can be decomposed and separated into any of these six simple machines.
A pulley is a simple machine that is made of a wheel found on an axle. This wheel will support a belt or cable that moves on the circumference of the wheel. Pulleys are used to apply forces, lift loads and transmit power. The original pulley was used to lift weights using a block and tackle. When a pulley if part of belt and chain drives then they transmit power between different shafts. There are three different types of pulley systems; fixed, movable and compound. A fixed pulley simple machine is one in which the axle of the wheel is attached to a support structure. The pulley will change the direction of a force on the belt or rope. Normally fixed pulleys are combined with another fixed pulley of a different size or a movable pulley. A movable pulley is one in which the axle is mounted on a block that can move. Unlike a fixed pulley a movable pulley has the equivalence of a mechanical advantage of two fixed pulleys. The compound pulley is a block and tackle that contains movable and fixed pulleys. This provides the most mechanical advantage or change of force.
A lever is a simple machine that contains a beam that is connected to the ground by a hinge. This hinge is also known as the fulcrum. The mechanical advantage of the lever is that it increases the input force in order to increase the output force and provides additional leverage. This leverage refers to the ratio of the input and output force. There are three leverage classifications which are based on the location of the fulcrum. Class 1 levers are those with the fulcrum located in the middle of the beam, examples being a seesaw or crowbar. Class 2 levers are those where the fulcrum is located on one side and force applied on the other, such as nutcrackers or a wheelbarrow. Class 3 levers are those where the fulcrum is located on one side but the input energy is applied in the middle of the beam, examples being a human mandible or tweezers.
A wedge is triangular in shape and is comprised on two inclined planes. It is typically used to separate tow objects, hold an object in place, lift an object or separate portions of an object. When force is applied to the blunt edge it then transmits this force to the inclined surfaces. The mechanical advantage is based on the ratio of the width to the slope length, so short wedges that have wide angles require more force than a long wedge that has a narrow angle. Wedges can lift very heavy objects by separating them from the surface where the heavy object is resting. As the wedge slides under the heavy object it object will slide up the sloped wedge side. Wedges can also hold items in place, an example being a door stop. This is accomplished due to the friction between the wedge and the floor and the wedge and the door.
Wheel & Axle
The wheel and axle is made up of both a wheel and axle that will rotate together. The wheel and axle is similar to a lever except that the input energy is applied to the end of the wheel which is perfectly balanced around the hinge. The distance from the hinge to the item being pulled shows the mechanical advantage. A good example of a wheel and axle is winch or windlass. Basically the power that is applied to the wheel must be the same as the power that is released. Therefore is power is applied to a large wheel then a smaller wheel at the other end will move much faster to release the same amount of energy. Therefore to turn the second wheel at the same speed much less force is required as input energy.
An inclined plane is best described as a ramp that is used to move loads down and up hills. Basically it is composed of a flat surface that is found at an angle when compared to the ground. This reduces the amount of energy needed to pull a load up the ramp. The mechanical advantage depends on the length and height of the inclined plane. Ramps can be fixed or portable and allow for easy loading of trucks. Siege ramps were used in ancient times to get heavy war machines to the tops of castle walls. Slides are used to transfer fragile objects, such as children, to the ground.
A screw is a simple machine that changes rotational force such as torque to a linear force. Most screws will have grooves, known as threads found along the outside of the screw. As the screw goes through a hole the threads on the inside of the hole will mesh with the threads on the screw. Rotating the screw will exert a force into the hole. A screw is normally either rotated through a threaded hole and an object or a nut that is rotated around a stationary screw. The simplest definition of a screw is an inclined plane that is then wrapped around a shaft. There are many items that used screw mechanisms besides screws including a corkscrew and water pumps such as Archimedes' screw.