Are you saying they do or do not move at the same speed? If you’re talking relative to the truck, they do. If you’re talking relative to the ground, they obviously don’t. I doubt people are confused by the concept as much as your ambiguous wording.
Or are people really that…simple?
Oh, Oh, okay, okay, imagine that a car is being driven through the mud. Also imagine that the car tires will sink into the mud. Now get a team of people to use lots of 8 foot long poles and that the people lay the poles out, from driverside tire to passenger side tire, right next to each other to form a layer of poles that the car can drive on. Now imagine that the car is slowly moving forward over the poles. As the car drives forward, poles from the back fo the car are carried to be placed in front of the car, creating more “road” for the car to drive on. The poles under the car are not moving, yet the car is moving forward.
Now imagine tying all the poles into the shape of a giant hamster wheel, large enough for the car to be inside of it. As the car drives forward, all the poles are moving, except the ones on the bottom.
Now cut the hamster wheel in two, down the center to create two hamster wheels, shrink the hamster wheels so they go under the car, over the front wheel, back under the car, and then over the back wheel. One on each side of the vehicle. Now you have the tread of a tracked vehicle.
Most tracked vehichles use skidding to turn by driving one track faster than the other. To turn left, stop the left track and drive forward on the right track. The vehicle will pivot on the left track as the right track goes forward.
How’s that?
Interesting. If the dozer driver knows he is moving at 10mph, he looks down to see that the lower track is moving rearward at 10mph (he’s literally outrunning the track like it’s sitting still) and the upper track is going forward twice as fast as the dozer. So “relative to the dozer’s speed” the tracks still move at different speeds.
But “relative to the dozer” is interesting. If you lift him up in the air, he would say both tracks are moving at 10 mph.
Wheel/axle/dozer tread physics assumes the groud is present so without the ground, is this now conveyor belt physics? Is there a difference?
Anyway, under normal circumstances, the driver and an outside observer both see the tracks moving at different speeds.
In the air the dozer is still relative to the ground and the bottom tread is moving backward relative to the ground.
On the ground the bottom tread is still relative to the ground and the dozer is moving forward.
(The competition here is not to explain this “illusion” (what illusion?) but to explain it to you and the kid.)
If you’re stuck in the mud, call a tow truck. You’ll spend more time and money finding eight foot poles, a team of people, and a giant hamster wheel.
What? No, that’s not right. The driver looks down and sees that he’s passing over the tread at 10 mph. He looks at the top of the tread and sees it’s passing him at 10 mph. Same speed.
For some reason, you switched points of view when you moved from the bottom to the top. You started with “relative to the driver” and ended with “relative to the ground”. As soon as you said “upper track is going forward twice as fast as the dozer”, you screwed up. How can it be going twice as fast if, from the driver’s perspective, the dozer isn’t moving at all?
From the ground, the dozer is at 10, the top tread is at 20 and the bottom is at 0. From the driver’s perspective, the top is +10, the dozer is 0, and the bottom is -10. If it were any other way, then the track pieces would be “bunching up” at the front of the vehicle!
You’re actually repeating what I said. I said that “If the dozer driver knows he is moving at 10mph”, then “relative to the dozer’s speed”, the driver can see the lower track going -v and the upper going 2v. But if you get rid of the ground then “relative to the dozer” itself, they both go v in different directions.
I think it’s interesting because this is the difference between driver and observer. “relative to the dozer’s speed” assumes the driver knows that he is moving, which is pretty much true 100% of the time, so it’s a difference that really only exists on paper. Must be why the math is geared toward the observer, dozer drivers who don’t know if they’re moving should probably concentrate on their job instead of doing math anyway.
No, I’m saying that this is completely false. Either it’s v and -v, or it’s 2v and 0. In no reference frame can you ever say that the bottom is -v and the top is 2v, like you’ve claimed. Those two numbers never go together, whether you’re on the ground or driving.
If you claim that the driver is the origin of our coordinate system (which is perfectly legit), then the top goes at 10mph, the tractor moves at 0mph (of course) and the bottom goes at -10mph. If you claim that the ground is the origin, then the top goes at 20mph, the tractor moves at 10 mph, and the bottom moves at 0mph.
Are you claiming otherwise?
Oops, in that post, I should have said lower track going 0 and the upper going 2v as I said earlier and which we agree on. Again, by knowing his speed, he has the same perspective as an outside observer, 2v and 0. By lifting him up in the air, he sees v and -v.
Other than that typo, I don’t see anything we’re not in agreement on. It may have been my wording to begin with. When I said:
“If the dozer driver knows he is moving at 10mph, he looks down to see that the lower track is moving rearward at 10mph (he’s literally outrunning the track like it’s sitting still) and the upper track is going forward twice as fast as the dozer.”
I didn’t mean the rear track is moving at -v, 10mph backwards. He sees it moving rearward at 10mph and he is moving at 10mph, thus he is outrunning it like it is standing still, because it is standing still. 2v and 0.