Tip:
Highlight text to annotate it
X
Gears are everywhere.
Cars, elevators, even bikes.
None of these objects works as well as they do without the use of gears.
But how can we understand what gears do?
We are going to take a close look at the gears and try to understand a little more about the physics, and engineering that makes them work.
Then we will use what we learned to try to understand how to win a bike race.
You are getting ready for a bike race.
The most important thing to know about is torque.
A torque is made up of the force and the distance. Force is a push or pull, and then force is applied at a certain distance away something that we will call the pivot point.
Watch as I try to push this revolving door.
It’s hard here,
but it is much easier here.
Why is that?
Well, if you are trying to push the door close to the pivot point, you need a big force.
As you move away from the pivot point, you increase of the distance component of torque.
And then you need to apply less force.
But what’s the tradeoff?
Let’s look at it at a top view.
This revolving door needs a certain torque to spin around.
You can get that torque by applying a big force at small distance away from the pivot point or small force at a big distance.
However, if you apply a large force, you only need to travel around a small circle to rotate once.
Smaller force is easier but you need to travel in a bigger circle.
Gears work in a similar way.
Gears touch each other and therefore apply a force to each other.
And the size of the gear is what that determines the distance, part of the torque.
One torque can drive the first gear, and you can get a different torque out the second gear.
In this case a bigger one.
So what’s the tradeoff?
Bigger gear provides a bigger torque but has to travel a longer distance before it spins around once.
Sound familiar?
Bikes use something called a sprocket which is essentially, a special gear for use for the chain.
For now let’s just say we can only change the size of the back sprocket.
The one that drives the back wheel.
But how will changing the sprocket size or shifting gears help you to be a better biker?
So to test this out, we’re going to have a race.
In this race, the first cyclist, me, is going to be stuck using a big sprocket.
Second cyclist is going to be stuck using a smaller one.
And they’re off.
Looks like cyclist 2 is after really early but cyclist 1 is pedaling furiously to keep up.
Oh it looks like cyclist 2 can’t get enough torque to get up that hill.
Cyclist 1 breezes past her.
Can cyclist 2 catch up on downhill?
And she does it.
It’s gotta be a close finish.
And cyclist 2 wins.
As you can see, using the larger sprocket is putting a huge torque on the wheel making the hill,
a piece of cake.
But to get anywhere, I had to paddle my legs off,
just like moving a revolving door far from the pivot point.
It’s easier, but there is more distance involved.
A smaller sprocket lets cycles to turn the wheel around many times.
But without the extra torque, she had trouble getting up that hill.
Just like moving the door close to the pivot point, it’s harder, but less distance is involved.
I hope you learned a little something about gears and the tradeoffs involved.
There is plenty more to learn.
See you next time.