How to Win a Bike Race: Using Gears - By MITK12Videos
Transcript
| 00:08 | gears are everywhere and cars , elevators . Mm Even | |
| 00:14 | bikes , none of these objects would work as well | |
| 00:17 | as they do without the use of gears . But | |
| 00:20 | how can we understand what gears do ? We're going | |
| 00:23 | to take a close look at gears and try and | |
| 00:25 | understand a little more of the physics and engineering that | |
| 00:28 | makes them work . Then we'll use what we've learned | |
| 00:31 | to try and understand how to win a bike race | |
| 00:34 | . Mm You're getting ready for a bike race . | |
| 00:41 | The most important thing to know about is torque . | |
| 00:45 | A torque is made up of a force and a | |
| 00:47 | distance . A force is a push or a pull | |
| 00:50 | and that force is applied at a certain distance away | |
| 00:53 | from something that will call the pivot point . Watch | |
| 00:57 | as I try to push this revolving door . It's | |
| 01:00 | hard here . What much easier here ? Why is | |
| 01:05 | that ? Well , when you're trying to push the | |
| 01:09 | door close to the pivot point , you need a | |
| 01:11 | big force . Yeah . As you move away from | |
| 01:15 | the pivot point , you increase the distance component of | |
| 01:18 | the torque and then you have to apply less force | |
| 01:21 | . But what's the trade off ? Let's take a | |
| 01:23 | look at a top view . This revolving door needs | |
| 01:26 | a certain torque to spin around . You can get | |
| 01:28 | that torque by applying a big force at a small | |
| 01:30 | distance away from the tipping point or a small force | |
| 01:34 | at a big distance . However , if you apply | |
| 01:38 | a large force , you only need to travel around | |
| 01:41 | a small circle to rotate once smaller forces easier , | |
| 01:45 | but you need to travel in a bigger circle , | |
| 01:49 | gears work in a similar way , gears touch each | |
| 01:52 | other and therefore apply a force to each other and | |
| 01:55 | the size of the gear is what determines the distance | |
| 01:58 | part of the torque want . Or can drive the | |
| 02:01 | first gear and you can get a different torque out | |
| 02:03 | of the second gear . In this case , a | |
| 02:05 | bigger one . The trade off bigger gear provides a | |
| 02:09 | bigger torque but has to travel a longer distance before | |
| 02:12 | it spins around once . Yeah , sound familiar bikes | |
| 02:21 | use something called a sprocket , which is essentially a | |
| 02:24 | special gear for use with a chain . For now | |
| 02:27 | , let's just say we can only change the size | |
| 02:30 | of the back sprocket , the one that drives the | |
| 02:32 | back wheel . But how will changing the sprocket size | |
| 02:35 | or shifting gears help you to be a better biker | |
| 02:38 | ? I don't know . So , to test this | |
| 02:44 | out , we're going to have a race in this | |
| 02:47 | race . The first cyclist me is going to be | |
| 02:49 | stuck using a big sprocket . Second cyclist is going | |
| 02:53 | to be stuck using a smaller one . Yeah , | |
| 03:20 | and there are , it looks like cyclist who is | |
| 03:22 | off to an early lead . The sightless one pedaling | |
| 03:25 | furiously . Keep up . Yeah . Oh , and | |
| 03:35 | it looks like cyclists to can't get enough torque to | |
| 03:37 | get up that hill , cyclist one breezes pastor can | |
| 03:41 | cyclists to catch up on the downhill . Mhm And | |
| 03:47 | she does it . It's gonna be a close finish | |
| 03:55 | and cyclists two wins as you can see using the | |
| 03:59 | larger sprocket . Let me put a huge torque on | |
| 04:02 | the wheel making the hill a piece of cake . | |
| 04:05 | But to get anywhere I had to pedal my legs | |
| 04:08 | off just like moving the revolving door far from the | |
| 04:11 | pivot point . It's easier but there is more distance | |
| 04:14 | involved . The smaller sprocket , let's cyclists to turn | |
| 04:20 | the wheel around many times , but without the extra | |
| 04:23 | torque , she had trouble getting up that hill , | |
| 04:26 | just like moving the door close to the pivot point | |
| 04:30 | , it's harder but less distance is involved . I | |
| 04:35 | hope you learned a little something about gears and the | |
| 04:38 | trade offs involved . There's still plenty more to learn | |
| 04:41 | . See you next time . Mhm Yeah , |
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