Gears, like any machine, give us a "mechanical advantage" to the work that we do. Probably the most obvious use of gears is on a bicycle. Most bicycles (even one-speeds) have a large gear at the pedals and a smaller one at the wheel. Set up this way, it means that for every one rotation of the pedal gear you gain more rotations on the wheel gear.

The illustration above shows a 2:1 gear ratio. This means that for every one turn of the pedal gear (blue), the wheel gear (red) turns two times. Pulleys act very similar to gears in this way. Instead of two gears with a chain between (like on a bike), you have two pulleys with a "belt" between. This is how your electric racer is set-up. Pulleys do offer some advantages over gears that we will discuss in a later chapter.


Which of the following statements are true about gears?

(Note: the questions are multiple choice and multiple answer. The student will need to check all the correct answers. This keeps the student from just "guessing" at the answers.)

A) They give a mechanical advantage.
B) They help us make forces larger.
C) Bicycles use them.

It is important to understand that gears and pulleys do not increase the power; they just spread the work accomplished over a greater distance. The person pedaling the bike does not suddenly become "more powerful" when he or she shifts gears to go up a steep hill, but the work is spread out over a greater distance (more turns of the pedal), making it easier.

Click on the first brick pile for option one.

It is important to notice that the amount of work accomplished was the same for both brick piles -- ten bricks from one side to the other. But the second option meant that we spread that work over much more time (ten trips instead of one) and therefore each trip was easier to do.

Which of the following statements is true about gears?

A) They make you more powerful.
B) They spread out work over a longer distance.
C) They give us a mechanical advantage.

How are pulleys like gears?

A) They are round.
B) They can have ratios to give us a mechanical advantage.
C) They can only do what gears do.

So now let's see how our understanding of gears, pulleys, and power translates to the electric racer.



When you use different pulley ratios, you change the force that is applied to an object. In other words, it seems like some pulley or gear ratios are stronger than others.


When we tested the speed of the car in different pulley ratios, we noticed that when the rubber band was on the large motor pulley, it went a lot faster. Do you think there will be a difference in the amount of weight the two different pulley ratios can carry? Which one will be able to carry more? Explain.

Record your answer in the logbook!



Racer, small (light) plastic cup (not too heavy -- a disposable paper or plastic cup will work), large cup with water.


Make sure your Racer is in high pulley ratio (rubber band from black pulley to front wheel) and that it has strong (new) batteries.


Set your racer up against a wall or back of a kitchen counter as shown. Turn on the car -- the wheels should just spin against the wall.


Place an empty plastic cup on top of the running racer. The wider the base of the cup the easier it will balance. (Note: a glass cup will be too heavy for this experiment. You may even want to use a paper cup.) The lighter the cup, the easier it will be to use. If you need to, you can gently hold it with your hand to keep it in place.

Slowly add water into the cup until the wheels stop spinning.

A. How much water did you add (how far up the glass did it go). Write your answer in the logbook.

Record your answer in the logbook!



This time put the racer into the low pulley ratio as shown. Special note: the reason for two rubber bands is so it won't slip on the motor shaft. However, if two rubber bands seems too tight, then just use one.

Place the cup on the car and slowly fill with water.



B. How much water did you add (how far up the glass did it go). Write your answer in the logbook.

Record your answer in the logbook. 


If you were to make up a theory (conclusion) from this experiment, what would it be? Why was the low pulley ratio stronger (kept going with more water)? (Hint: it has to do with spreading work over more time)

Record your answer in the logbook.



© 2003-2016 Exploration EducationTM. All rights reserved

NOTICE: This online curriculum is authorized solely for the individual who purchased this curriculum. This online curriculum is protected by copyright law and international treaties. Unauthorized reproduction or distribution of this program or any portion of it may result in severe civil and criminal penalties, and will be prosecuted to the maximum extent possible under the law. Absolutely no images, animations, or movies on this online curriculum may be used on a web site, or reproduced on electronic media or in printed form.