Simple Machines, Industrial Tools and Equipment
Simple Machines are those four classic devices from which all other machines were built: they are the lever, the pulley, the inclined plane, and the wheel and axle. The amazing thing is that while these simple machines have been around for thousands of years, no other simple machines have been discovered. Even the screw and the wedge are based on the inclined plane. Cars, robots, power and machine tools, are all based on these four simple machines. No matter how complicated a machine might be, it is composed of some combination of these four simple machines.
We like simple machines because they make our lives easier by making it possible for us to spend less energy while producing the same amount of work. These machines reduce the amount of energy we need to perform work by 1) reducing the amount of force needed to move an object, and 2) by changing the direction in which the force must be applied, or 3) by doing both. Machines make it easier to do things by making it possible for us to apply less force or to apply force in a direction that is easier to manipulate. Machines reduce the force needed to perform work by increasing the distance over which the force is applied. So, even though less force is being used, the amount of work remains the same. Some common examples of simple machines are the shovel (a form of a lever), the winch in the car garage, the steering wheel of a tractor (wheel and axle), and the wheelchair ramp which is basically a form of the inclined plane. A classic example of a complex machine is the can opener which combines a lever, a wheel and axle and an inclined plane.
How
Simple Machines Work
Simple machines help us to accomplish more by reducing the amount of force
required to move an object a specified distance. Work, in physics, is the amount of force used to move an object multiplied by the distance
over which the force is applied. This can be written in mathematical terms:
| Work = Force × Distance |
Force is the push or a pull exerted on one body by another, i.e., a hand pushing a plate across a table. Distance is the distance a load is moved by the force. Simple machines are useful because they multiply the force exerted to perform a task. The advantage that it gives us by reducing the amount of required force is called the machine’s mechanical advantage (MA). We can find the mechanical advantage of a machine by dividing the force the machine delivers by the effort put into the machine. The ideal mechanical advantage of a machine is the advantage it would produce if the machine were perfect, i.e., were without friction. Friction always opposes motion and makes doing work harder. Since friction is present in every machine, the actual mechanical advantage is always less than the ideal mechanical advantage. Get your Channellock Griplock Tongue and Groove Pliers Set — 3 Piece and more from Northern Tools & Equipment. |
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If we know the mechanical advantage of a machine. we can predict how much force is needed to lift a given object. Consider the inclined plane: the amount of work needed to overcome friction or gravity and lift a given load always remains the same. An inclined plane spreads the necessary effort out over a longer distance making the task easier. This explains why walking up a gentle slope is easier than walking up a steep slope. The distance walked on the gentle slope is longer, but the effort needed to reach the top is less.
Applying
effort over a greater distance may reduce the amount of force required, but it takes more time slowing down the speed of work. Some machines can
actually speed up a task. They do this by reducing the distance over which the effort is applied. If the distance in the equation defining work is
reduced, then the force must therefore be increased to keep work constant. Increasing the speed at which a task is performed requires more force
than would otherwise be necessary. The wheel and axle and certain types of levers are simple machines that can either speed up a task (requiring
more effort) or slow down a task (requiring less effort). A great example is the 10 gear bicycle. While some gears require that you try harder to
achieve higher speeds, other gears require less effort and are useful for climbing hills.
While most simple machines rely on hand power, complex machines like the airplane
and the elevator do not. They use the energy stored in chemical substances, such as airplane fuel or the energy stored in electricity, to provide
the necessary force to do work. An airplane engine uses the combustion, or rapid burning, of airplane fuel to power the engine that turns the
propeller. An elevator uses large engines, usually powered by electricity, to pull cables that raise and lower the elevator car. Electricity also
powers the levers that help open and shut the elevator doors.
Examples of Simple Machines
Inclined
plane - a device that reduces the force necessary to move a load a certain distance up by providing a path for the load to move at a low
angle to the ground. This lessens the needed force but increases the distance involved, so that the amount of work stays the same.
Lever - from the old french levier, to raise, is a bar or rod that rotates around a fulcrum and multiplies the mechanical force applied to one part of the bar. When effort is applied at some point on the bar, the bar rotates around the fulcrum and raises a load. There are three classes of levers: first, second and third class levers. First class levers always have the fulcrum between the effort and the load, i.e., pliers. Second class levers always place the load between the fulcrum and the effort, i.e., a wheelbarrow. Third class levers place the effort between the load and the fulcrum, i.e., a catapult.
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Pulley - is a wheel with a groove along its edge, for holding a rope or cable. Pulleys can be used in sets designed to reduce the amount of
force needed to lift a load. Check out the very popular 2000-Lb. Pulley Hoist from Northern Industrial Tools - Lawn + Garden
Wheel and Axle - consists of a handwheel (a disc or lever arm with a handle) which turns an axle around which a chord is wound. Visit Northern
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Gear - is a kind of wheel with teeth designed to transmit torque to another gear or toothed component. The
teeth of a gear are shaped to minimize wear, vibration and noise, and to maximize the efficiency of power transmission.
Screw - is a shaft with a helical groove formed on its surface. It is used as a threaded fastener to hold objects together, and as a device
used to translate torque into linear force.
Wedge - a form of inclined plane, a wedge is a device used to separate
two objects through the application of force, perpendicular to the inclined surfaces, developed by conversion of force applied to the blunt end. The
mechanical advantage of a wedge depends on the ratio of it length to its thickness.