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It’s a hot summer day. You have to get a big box of toys down the street to a friend’s house. Do you think you would use a square-wheeled cart? How about a wooden sleigh? Perhaps, you’d just carry it. Or maybe, just maybe, you’d use a wagon. Why would the wagon be the best? It’s because rolling is easier than carrying or sliding. This lesson helps you look at ways that rollers and wheels and axles make life easier.
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Rollers, balls, and wheels are all different shapes, but they all roll. It’s much easier to roll something across the floor than to slide it across the floor. There is less friction. Less friction means it’s easier to move things.
Today, let’s start with an activity using rollers. You get to test the theory that rolling things is less work than sliding them.
Activity 2: Easy Roller
Is rolling a load easier than sliding it?
What you need
- string
- several round pencils
- a small cardboard box, such as a shoe box
- rocks, marbles, or other objects to put in the box
What to do
Look at the diagram to help with this activity.
1. Fill the box with several marbles or rocks or similar objects.
2. Tie the string around the sides of the box and leave a long end to pull on.
3. Pull the box across the table. What do you notice?
4. Place at least 4 pencils under the box. Put 2 or more pencils in front of the box. Line up all the pencils evenly. (See the diagram at the start of this activity.)
5. Pull the box across the table. Explain the difference between pulling the box with and without the pencils.
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Huge 4000-kg blocks of stone make up the pyramids in Egypt. How were people able to move such huge rocks? There are many different ideas. One theory is that the workers rolled the stones on round logs. It was like rolling the box on pencils in Activity 2.
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Rollers are tube-like shapes (or cylinders). If you turn a tin can on its side, you have a roller. If you want to pull a small boat up a beach, you can first lay down some rollers, such as long, smooth poles. You would place them in the path of the boat and then pull the boat onto the rollers. Again, it’s like your box-and-pencil activity.
Roller conveyors also use rollers. A long line of rollers helps move heavy objects over a long distance.
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Conveyor belts are quite similar. A belt covers the rollers and moves the object. For example, bags checked at an airport ride on a conveyor belt. Farmers may use conveyor belts when they store or stack bales of straw and hay up high.
A wheel is simply a new and improved version of a roller. A wheel and axle is a simple machine. The wheel is connected to a cylinder or rod (the axle). It acts like a roller.
Where have you seen a wheel and axle? You would probably guess correctly that they are found on vehicles. Did you know they are also found on the door to your room? When you turn a doorknob to open a door, you have used a wheel and axle.
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In a wheel and axle, a wheel is attached to a cylinder or rod called the axle. If the wheel is turned, the axle also turns. If the axle is turned, the wheel also turns.
Think of a steering wheel in a car or even a go-cart. The part the driver holds is the wheel. The column that attaches to the wheel is the axle. The driver applies force to the wheel to steer the vehicle.
The most common use of the wheel and axle is to make vehicles move. When you pedal your bicycle, you apply force to the axle of the rear wheel. It turns, and the wheel turns with the axle. In cars and trucks, the engine supplies the force that turns the axles and wheels.
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Machines with wheels and axles are Ferris wheels, gears, water taps, and hamster exercise wheels.
Sometimes an idea is so good, you just use it over and over again. That nice round wheel is one good idea. You see it used all over the place. The wheel and axle is only one simple machine that uses it. You’ll see that round shape many more times in this module.
3. Pull the box across the table. What do you notice?
It is difficult to pull the box. It takes a lot of effort to pull the box.
5. Pull the box across the table. Explain the difference between pulling the box with and without the pencils.
It is much easier to pull the box when it is on rollers (the pencils).
Copyright © 2006, Alberta Education.
