TRYING OUT GEARS

You Will Need:

• Assorted sizes of clean, empty cans

• Glue

• A corrugated cardboard box

• X-Acto knife

• Scissors

MAKING YOUR GEARS

Cut your corrugated cardboard box into flat pieces, making sure that you cut off all the folds, and bends from your pieces.  Peel the paper layer completely off of one side of these pieces, exposing the inner corrugated piece.  (You can also buy corrugated packing material that looks like your corrugate would look after peeling.  Another option is to buy colored corrugate at a party shop.)

Cut your peeled corrugated pieces so that they will fit neatly around the cans, fully covering the outside of the can.  The lines of the corrugate ribs must go up and down on the sides of the can, not around the circumference of it. Glue the peeled corrugate pieces to the outside of the cans.  Make sure your ends but up neatly, so that you can't tell where the seam is. Repeat this process for your other cans.

EXPERIMENTING WITH YOUR GEARS

1. Set two gears, the same size, on the table together so that the gears mesh (meshing gears mean that the high parts of the teeth on one gear fit into the valleys between teeth on the other gear).  While holding onto the gears, so that they don't separate, slowly turn one of them.  What happens to the other one?  How fast does it turn?  What direction does it turn?  How hard is it to turn?

2. Now, try the same thing with two gears that are different sizes.  Turn the larger one first.  What happens to the smaller one?  Then try turning the smaller one.  What happens to the larger one?   How fast does it turn?  What direction does it turn?  How hard is it to turn?

3. Try connecting three or four gears together, going from largest to smallest.  You might need to get someone to help you hold them.  Turn the largest one, and see what happens to the smallest one.   How fast does it turn?  What direction does it turn?  How hard is it to turn?  Then try turning the smallest one, and see what happens to the largest one.   How fast does it turn?  What direction does it turn?  How hard is it to turn? 

EXPLAINING HOW IT WORKS

Gears are used for a variety of purposes in machines.  Basically, they perform four functions:

• Changing the direction something is turning (you can even change direction at a right angle).

• Changing the speed something is turning (this is the most common usage of gears).

• Changing the amount of power available coming out of a motor or other power source.

• Moving motion from one place in a machine to another.

In your first experiment, you should have noticed that the second gear turned in a direction opposite of the first.  When one gear turns, any gear connected to it ends up turning in the opposite direction.  If you want it to turn the same way, like on a bicycle, you have to put a chain connecting the gears.  

In your second experiment, you should have noticed that the small gear turned much faster than the large gear.  This would be true whether you turn the small gear, or turn the large gear.  The large gear has many more teeth on it than the small one.  Since the teeth on the gear must move exactly together, and the large gear has more teeth, the small gear must turn more times than the large one.  In a car transmission,(as well as many other types of machinery), this principle is used to allow the vehicle to change to different speed ranges.

You should have also noticed that it was easier to stop the small gear than the large gear.  As the speed decreases (gets lower) the strength, or torque, increases.  So, a very small fast moving motor, when it is going through a bunch of gears, can provide a lot of power at a much slower speed.

When you put the chain of gears together, you should have noticed that the smallest gear was moving very fast, while the largest gear was moving very slow.  A chain of gears like this can be used to supply power to several different things in a machine at the same time.  Each of them would receive the rotational movement at the exact speed that they need it, while all of the items were still connected together.  So, if you needed to speed the whole thing up, everything would speed up the same amount.  

Analog watches use a chain of gears like this.  The second hand is attached to one gear, the minute hand to another, and the hour hand to still another.  Although they are all connected together, synchronized with each other, each one is moving at its own speed.

Almost all mechanical machines use gears in some way.  Look around you to see what you can find in your house that uses gears.