All big machines are made up of combinations of smaller parts, including lots of gears. Experiment with gears and simple machines with hands-on projects!
Gears can help us do work by speeding up or changing the direction of motion. To see how this works, make a model set of gears!
You've just built a gear train. The big gear is the driver. Try turning it slowly. What happens to the little gear? Which way does it turn? Draw a big colorful dot on each gear, and position the gears so that both dots are at the top. As you turn the big gear, have one person count how many times the big gear turns all the way around and another person count how many times the small gear does. Do they turn the same number of times?
Gears work to change the direction of motion. When you turned the big gear one way, the little gear turned the other way! Gears also change speed of motion. When you turn the big gear slowly, the smaller gear turns faster. This helps save energy, because you don't have to work as hard to turn the big one slowly as if you had to turn the small one quickly.
You can also try this project with water bottle caps that have ridges, or with gears from a building set like Lego or K'Nex.
An inclined plane, such as a ramp, is a kind of simple machine that helps do work. A screw, just like the ones from a hardware store, is also a simple machine! A screw is made from an inclined plane being wrapped around and around. To see how this works, you will need notebook paper, and a pencil or marker.
Because of the inclined plane, screws can hold all sorts of things together. If you like, try making different shapes and sizes of triangles, and wrap them around a marker or pencil to make different kinds of screws.
When you think of a machine, you probably think of something big like a washing machine or car or bulldozer. Those big machines are made up of smaller parts called simple machines. Simple machines are made of one or two parts, and they help us do work like making things move. There are several different kinds of simple machines:
Gears are also important simple machines. A gear is just a wheel with teeth, sometimes called a cog. To do any work with a gear, you need to have at least two cogs with their teeth fitting into each other. Because the teeth fit together, when you turn one gear, the other one turns too! Gears come in many different sizes, which help them do work. If you connect one big gear with a small one, you can turn the big gear slowly and it will make the little gear turn quickly. Since it takes less energy to turn the big gear slowly than it would to turn the little one quickly, you are saving energy and making work easier by using gears.
One gear can make another one turn faster, but it can also make it turn in a different direction. When you turn a big gear to the right, the little one will move to the left. This is good for many machines where the direction needs to change in order for the machine to work.
When two or more gears are connected, it's called a 'gear train.' The gear that you turn is called the 'driver' and the last gear that you are trying to move is called the 'driven' gear. Sometimes there will be several gears in between the driver and the driven—those are called 'idlers.'
Gears are everywhere! Some rides at an amusement park or fair use large gears which make them spin in circles (like the spinning teacup ride at Disneyland). Huge wind turbines use gears to convert the slow motion of the blades into much faster motion to make electricity.
Gears are in small things, too, like tiny music boxes or remote controlled cars. They are used in clocks to make the minute and the hour hand go around. They are used in motors: big car motors, and little motors that make your toys move. Most of the time they are hidden away inside so you can't see them, but if you look at a can opener, you will be able to see two gears. Turning the handle will make one of the gears move, and the other one will move in the opposite direction. You can also see gears on a bicycle. With some bikes, the wheels will move at different speeds when you pedal because of gears connected by a chain.
Use this worksheet to help review the concepts of how gears change speed and direction. The bottom half is the pattern for the 'Experiment with Gears' project.
You can make different gear patterns using this gear template generator.