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Hi everyone! Today we're going to talk about simple machines.
A simple machine is a device that makes work easier by magnifying or changing the direction
of a force. That means that simple machines allow someone to do the same work with less
effort! Simple machines have been known since prehistoric times and were used to help build
the amazing structures left behind by ancient cultures.
The Greek philosopher Archimedes identified three simple machines more than 2,000 years
ago: the lever, the pulley, and the screw. He discovered that a lever would create a
mechanical advantage, which means that using a lever would allow a person to move something
that would normally be too heavy for them to shift. Archimedes said that with a long
enough lever and a place to rest it, a person could move the world.
Over the next few centuries more simple machines were recognized but it was less than 450 years
ago that the last of the simple machines, the inclined plane, was identified.
There are six types of simple machines: the Lever, the Wheel and Axle, the Pulley, the
Inclined plane, the Wedge, and the Screw. Pulleys and Wheel and Axles are both a type
of Lever. Wedges and Screws are both types of Inclined Planes. Each type of Simple Machine
has a specific purpose and way they help do work.
When speaking of simple machines, 'work' means using energy to move an object across a distance.
The further you have to move the object, the more energy it takes to move it. Let's see
how each type of simple machine helps do work.
A LEVER is a tool like a bar or rod that sits and turns on a fixed support called a fulcrum.
When you use a lever, you apply a small force over a long distance, and the lever converts
it to a larger force over a shorter distance. Some examples of levers are seesaws, crowbars,
and tweezers.
A Wheel and Axle is easy to recognize. It consists of a wheel with a rod in the middle.
You probably already know that it's easier to move something heavy if you can put it
in something with wheels, but you might not know why. For one thing, using wheels reduces
the friction - or resistance between surfaces - between the load and the ground. Secondly,
much like the lever, a smaller force applied to the rim of the wheel is converted to a
larger force traveling a smaller distance at the axle. Wheel and axles are used for
machines such as cars, bicycles, and scooters, but they are also used in other ways, like
doorknobs and pencil sharpeners.
A Pulley is a machine that uses a wheel with a rope wrapped around it. The wheel often
has a groove in it, which the rope fits into. One end of the rope goes around the load,
and the other end is where you apply the force. Pulleys can be used to move loads or change
the direction of the force you are using, and help make work easier by allowing you
to spread a weaker force out along a longer path to accomplish a job. By linking multiple
pulleys together, you can do the same job with even less force, because you are applying
the force along a much longer distance. Pulleys may be used to raise and lower flags, blinds,
or sails, and are used to help raise and lower elevators.
An Inclined Plane is a flat surface with one end higher than the other. Inclined planes
allow loads to slide up to a higher level instead of being lifted, which allows the
work to be accomplished with a smaller force spread over a longer distance. You may recognize
an inclined plane as the simple machine used in ramps and slides.
A Wedge is simply two inclined planes placed back to back. It is used to push two objects
apart. A smaller force applied to the back of the wedge is converted to a greater force
in a small area at the tip of the wedge. Examples of wedges are axes, knives, and chisels.
A Screw is basically an inclined plane wrapped around a pole. Screws can be used to hold
things together or to lift things. Just like the inclined plane, the longer the path the
force takes, the less force is required to do the work. Screws with more threads take
less force to do a job since the force has to travel a longer distance. Examples of screws
are screws, nuts, bolts, jar lids, and lightbulbs.
These six simple machines can be combined to form compound or complex machines, and
are considered by some to be the foundation of all machinery. For example, a wheelbarrow
is made of levers combined with a wheel and axle. A pair of scissors is another complex
machine: the two blades are wedges, but they are connected by a lever that allows them
to come together and cut.
We use simple machines to help us do work every day. Every time you open a door or a
bottle, cut up your food, or even just climb stairs, you are using simple machines. Take
a look and see if you can identify the simple machines around you and figure out how they
make it easier to do work.