At the beginning early man used his hands, feet and teeth to do work with. They lifted and carried objects with his hand and cut things for food by biting with their teeth. Gradually they searched for ways to make their work easier.
Among the most useful, simple machines devised by human are levers, the wheel and axle, pulleys, inclined planes and screws. Simple machines are the most basic of the machines that we use daily to make work easier.
We use simple to complex machines in our daily routines such as to clean, move, create, repair, relax, have fun, and accomplish work. All of today’s complicated machines are based on these simple machines used long ago.
There are six simple machines devised by human – levers, wheel and axle, pulleys, inclined planes, screws and wedges.
The simple machines require human energy in order to work. A machine makes our work easier implies that we need less force to do the same amount of work.
What is a machine?
You must have sometime noticed a mechanic replacing a tyre using jack. He uses jack to ease his work as automobile has to be lifted which he himself alone can’t do. With the use of jack he lifts the automobile with less effort.
So, Machines are devices, which help us to do a great deal of work with less effort.
Simple machines have few or no moving parts to them. These machines help us to move objects closer, apart, or to raise them to different levels by increasing the force or changing the direction of the force.
Have you tried to move a big stone?
First try with your hand.
What do you observe?
Rock does not move at all.
Now try this way, placing a smaller stone near the larger stone and placing a one end of wooden stick under the larger stone and supported it on the smaller stone, then pressed down on the other end of the stick.
What do you think happened?
The big stone moves. The stick helped you to lift or move the stone more easily or with less effort.
When a long plank or pole is used to lift a large load, it is called a lever. This type of lever is called a crowbar.
A lever consists of a rigid bar, which is free to turn about a fixed point called a fulcrum. The fulcrum is a pivot point. The effort force (push or pull) is exerted upon one lever arm, and the other lever arm will go up or down in the opposite direction.
The idea of a lever is based on three things – effort or force, distance and balance. The downward force that the man applies to one end is called the effort. A lever’s balance point is called its fulcrum. The fulcrum is the part of the machine that does not move.
The force is applied at a different point from the load. The closer the fulcrum to the load, the less force needed to lift the load.
The closer the fulcrum to the force, the greater the force needed to lift the load. The force will move a shorter distance, and the load will move a greater distance.
There are mainly 3 types of levers depending on the position of the fulcrum.
Class – I Lever: The lever has the fulcrum in the middle, between the load and the effort. Classic example is see saw.
Other first class levers include: a car jack, a pair of pliers, a pair of scissors, a water pump, a balance or pair of weigh scales, a crowbar, a claw of a hammer taking out a nail, or a lever with a rock as its fulcrum trying to lift another rock.
Class – II Lever: The lever has the load in
the middle, between the effort and the fulcrum. In the second class lever, the
fulcrum is usually closer to the load, which reduces the force needed to
accomplish the work.
Example: wheelbarrow. The axle of the wheel acts as the fulcrum, the handles are the force arm, and the load is carried between the two in the bucket part of the wheel barrow.
Other second class levers include: a pair of nutcrackers, and a bottle opener.
Class – III Lever: The lever has the effort in the middle, between the load and the fulcrum. This arrangement requires large force is to move the load. But this arrangement facilitates movement of the load over a long distance with a relatively small movement of the force arm.
Examples of third class levers are: a fishing pole, a pair of tweezers, an arm lifting a weight, a pair of calipers, a person using a broom, a hockey stick, a tennis racket, a spade, or a shovel.
Wheel And Axle
Try to turn a doorknob without the knob. Do you find it hard to turn? Try it with the knob attached. Is it easier?
No one knows when the wheel was invented but it is the one of the most important invention of human beings. We cannot even imagine our lives without any vehicles and all other wonderful machines around us.
Wheel as such is not a machine by itself but becomes a machine when a rod called an axle is attached to it. Together, the wheel and the axle make a simple machine. We can see such an arrangement in cars, sewing machines, egg beaters, bicycles, the potter’s wheel etc.
Other examples are a water wheel, a windmill, gears, doorknobs, faucet handles, and steering wheels.
Interesting fact: The wheel and axle is a first class lever in which the fulcrum has been replaced by an axle and the arms have been repeated around the axle to make up the spokes or disk of the wheel. This allows the lever to rotate through 360º instead of the limited rotation in the see - saw application. The larger the wheel, the more mechanical advantage we have.
A pulley is wheel that has a grooved track for the rope, belt or chain to move through it. A pulley is a circular lever, with the wheel rotating freely on the axle. A fixed pulley is fixed firmly attached to one spot, and does not move around. It does not cause change in force, distance or speed, but it changes the direction of the force.
Fixed Pulley - A fixed pulley acts as a first class lever. The fulcrum is the axle (the point at which the pulley is supported). In a pulley, an effort is applied in one direction and a load moves in another direction. The force arm is the radius of the pulley - that is, the distance from the fulcrum (axle) to the side of the rope on which we pull. The load arm is also the radius of the pulley - the distance from the fulcrum (axle) to the load-carrying side of the rope.
Examples of fixed pulleys can be seen on flag poles, drapes, or on a sail mast. A pulley is used to pull up water from the wells by pulling the rope down. At the top of most sailboats there is a single fixed pulley for raising and lowering a sail. A flag is raised on a flag pole with a pulley
Movable Pulley - A movable pulley moves along a rope or wire. It causes increase in force. A movable pulley works like a turning second class lever. The fulcrum is at one rim of the pulley wheel, the load is at the axle, and the force is at the other rim of the pulley wheel.
Pulleys make lifting easier because more sections of rope are supporting the weight. It is much easier to pull down than to pull up a load, as our own body weight and gravity help us to pull down. Thus, a pulley is used extensively to do twice as much work with the same effort.
The word "inclined" means "at an angle". The word "plane" means "a flat surface". An inclined plane is a slope or a ramp. Examples : a ramp used by a workman to push a heavy load on wheels up into a truck, ramps for wheel chairs, ramps to load luggage onto a plane, an escalator, slope such as the side of a hill, which is a natural inclined plane. Though, roads in the hills make longer distances, but are easier than climbing straight up!
Have you ever observed workers loading heavy objects in a truck?
An inclined plane helps a person to move or raise heavy objects. An inclined plane enables a load to be lifted with less force, but the distance over which it moves is greater. If ramp is longer, person will need less force to move the object up the ramp compared to shorter ramp.
A double wedge is made up of two inclined planes back to back. Example: double wedge on an axe blade. Single wedges resemble an inclined plane, because they have only one sloping surface. A doorstop is a single wedge.
Other examples are a chisel, cutting tools, an axe (also a lever), a can opener (also a lever), plow blade, and the bow of a boat or ship.
A screw is yet another simple machine, which is an inclined plane wrapped around a cylinder. The inclined plane forms ridges in a spiral along the cylinder. These ridges are called the threads of the screw. The distance between the threads is called "the pitch" of the screw.
Screw is inserted into a piece of wood using a screwdriver. It is difficult to pull out a screw out of a piece of wood compared to a nail. This is because a screw is really an inclined plane that goes round and round. Thus, it holds things together, through a longer distance with a stronger grip.
We use screws to do many jobs. Bolts are used to put together many small parts of complex machines, revolving stools, bases of most light bulbs. Even your pen caps have screws.
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