SCIENCE
Machines
Machines are everywhere!
They help us do things, or make doing them easier.
Every time you play on a see-saw, you are using a machine!
A lever is a stiff bar that tilts at a point called the pivot or fulcrum.
The pivot of the see-saw is in the middle.
Using the see-saw as a lever, a small person can lift big person by sitting further from the pivot.
On a see-saw lever, the pivot is in the middle.
Other levers have pivots at the end.
Screw-jack
The screw is another simple but useful scientific machine.
It is a ridge, or thread, wrapped around a bar or pole.
It changes a small turning motion into a powerful pulling or lifting movement.
Wood-screw hold together furniture or shelves.
A car jack lets you lift up a whole car.
Wheels
Where would you be without wheels?
(A car’s rear wheels are turned by axles.)
Not going very far.
The wheel is a simple machine, a circular disc that turns around it’s center on a bar called an axle.
Wheels carry heavy weights easily.
There are giant wheels on big trucks and trains and small wheels on roller-blades.
Pulley
A pulley turns around, like a wheel.
(Two pulleys together reduce the force needed to lift a heavy girder by one half.)
It has a groove around it’s edge for a cable or rope.
Lots of pulleys allow us to lift very heavy weights easily.
The pulleys on a tower crane can lift huge steel girders to the top of skyscraper.
GEARS
Gears are like wheels, with pointed teeth around the edges.
(Gears change the turning direction of a force.
They can slow it down or speed it up and even convert it into a sliding force {rack and pinion}.)
They change a fast, weak turning force into a slow, powerful one- or the other way around.
On a bicycle, you can pedal up the steepest hill in bottom(lowest) gear, then speed down other side in top (highest) gear.
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