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Sometimes concepts build on one another in succession.

Sometimes they don’t.

These thoughts on the concept of torque are a follow up to the Beginner’s Guide to Learning about Gears.

My husband Dan designed this activity to teach his *FIRST LEGO League* teams what torque is and how it affects Mindstorms robots.

Any time you want a mechanical machine to do a lot work of like lifting while pulling, pushing, and turning, you want a sturdy build.

You want the machine to withstand the force put on it when it’s performing the task you want it to do.

**The Beginner’s Guide to Experimenting with Torque** will teach you and your students about torque and how to apply it.

## Definition of Torque

Torque is a force that wants to twist something instead of just pushing or pulling it. Any time you are rolling or turning something, chances are you are applying some torque.

For this activity, we’ll be using our LEGO Technic pieces again to build a lever where you can change the location of the baskets you hang at the end of the beams.

Remember that Technic pieces are easily found in LEGO sets that require those pieces like Bionicles or Star Wars sets among others. If you have a hardcore LEGO kid, chances are you have some pieces on hand.

## Experimenting with Torque

For this activity you will need:

**Technic LEGOs**– Beams and pegs of various sizes**Build Directions**– You can download this set of directions onto any device and use them to build the lever apparatus.**Data Sheet**– Print this form so your students can record their results in the chart.

Once you have the lever machine built, you can continue with the experiment.

- The data chart tells you how to set up each trial of the experiment.
- You’ll be changing the location of the nickel baskets according to each row of the chart.
- Make a hypothesis about how the torque will be affected as you move the basket closer or farther away from the axle.

For example, for the first trial, count from the axle out 15 holes and place the basket at the very end. On the opposite side, put the basket 9 holes out.

- On the side with 15, place three nickels.
- Now place the nickels in the basket on the other side and determine how many nickels it will take to balance the machine.
- When you record your nickels, remember to add 2 nickels to account for the weight of the basket.
- Repeat this procedure for each row of the chart.
- Use the blank rows of the chart to make up your own, if you’d like.

## Calculate the Torque

Now it’s time to use the data you collected to calculate and determine the torque produced to balance the beam.

Remember that scientists need to analyze data before they can interpret what it’s telling them. We will calculate the torque by using the following formula:

*Torque = Holes x Nickels*

*Torque = Holes x Nickels*

In our case, the units will be *holes • nickels*. Make sure you’ve added the two nickels for each basket or the math doesn’t work out in reverse.

Torque is **distance times force** (τ = r · *F*) and the unit is Newton meters (N m).

For us, the distance is the measurement from the axle to the hole with the basket and the force is the number of nickels.

*How does the torque change as you move the basket on the beam?*

**Pro Tip**– You will find that the smaller the distance, the smaller the torque. Think of it in terms of where you place a door knob on a door. Since you shorten the distance between the hinge and the knob you don’t produce a lot of torque which makes it harder to open the door.

Which really makes me wonder about Hobbit hole doors.

## Resources for Studying Torque

We are big fans of Crash Course at our house. This video is a high school level physics discussion of torque and you’ll get a little Calculus splashed in, but if you have kids who like to know more…this is it.

**Bozeman Science Torque**– Another video that explains torque with a lever arm and how it works very similar to our experiment.

## Sled Pull Challenge to Experiment with Torque

*I received the Sled Pull Challenge kit from Pitsco Education. The opinions on this kit are entirely my own.*

Now that we know a little about what torque is and how to calculate it, it’s time to apply our knowledge.

That’s the fun of science. You get to apply what you learn.

Directly.

To real life.

And tractors.

Because tractors do a lot of work.

Torque where tractors are concerned is a big deal.

The Sled Pull Challenge from Pitsco Education, provides the materials you need to build a tractor and a sled which can be pulled by the tractor.

For this challenge you will need:

- building pieces for the tractor- and instructions
- pieces for the sled- and the instructions
- gears of varying sizes
- large rubber bands- to change the tread on the tractor wheels
- axles- to adorn the tractor with wheels
- screwdriver- to tighten the screws
- a clear area to operate the tractor
- an inclined plane – so you can make the tractor pull uphill

Do you see those wheels again? Remember how excited I was about them? I’m no less excited this time around.

Because sturdy, reliable building materials are pretty amazing.

Once you have the tractor and the sled built, it’s time to power up the tractor and see what she can do.

What’s next?

- You can make it go.
- Make it go by pulling the sled, after attaching the two with string.
- Change the material around the large wheels of the tractor- see how the friction affects performance.
- Add weight to the sled by piling on more washers.
- Use the inclined plane to see how the tractor can pull its load up hill.
- Change the gears to change how much work the tractor can do.

This is where torque comes in. And what was that about changing gears?

That’s the gear ratio.

## How Gear Ratios Affect Torque

Are you feeling like an expert yet?

Give it some time.

Let’s talk about gear ratios.

When you put two different sized gears together to do work, they aren’t working in exactly the same way.

Naturally, just like if you are walking with someone with way longer legs than you, you’ll be taking more steps to go the same distance than your long-legged pal.

Gears work the same way.

Bigger gears have more teeth and a bigger circumference than smaller gears.

They will make more revolutions in a given time than their bigger gear counterparts.

**Gear ratios** are the *ratio of the number of teeth in one gear to that of another*.

So, if you have a gear with twice the number of teeth as the gear next to it, it will have twice the circumference of the small gear.

It will turn with two times the torque and half the speed of the small gear and in the opposite direction.

Torque is the force exerted as the gears are turned.

If you are doing the Sled Pull Challenge, you can change the sizes of the gears to change the torque applied to the tractor wheels.

Then you can observe which gear ratio arrangement can pull more weight.

Or climb the hill better.

As always, have your students make predictions about which gear ratio will work the best for pulling more weight or climbing.

Then test it out!

That’s all there is to it.

By now, maybe you feel like you can take on AP Physics. Right?

Great job!

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