Something amazing to tell you concerning physics and motion

[Jenson71]

This blows my mind.

Okay, say you have two ball bearings. You hold one in your hand and drop it. The other you put in a gun, point it straight forward, as level as the one in your hand, and pull the trigger, sending it hundreds of yards.

Which one lands first?

The one dropped in your hand right? RIGHT!?!?

No, actually they both hit the ground at the same time.

This is because the vertical component of motion is the same for both objects. They both fall vertically the same distance at about 10 meters per second squared (gravity, actually more like 9.8).

But Jenson, Jenson! What about the horizontal component of the gun-fired ball bearing? Actually, when air resistance is small enough to ignore as it is in this case (being that the bearings are exactly alike), the horizontal and vertical components of a projectile's velocity are completely independent of one another.

And, in this experiment, the gun-fired bearing is constantly falling from the moment it is fired. Yes, it looks like it is holding up in a straight line, but, it's actually falling and it's just hard to see with our eyes. And again, it is falling at exactly the same speed as the ball bearing you released in your hand -- the speed of gravity.

Post more cool science things in this thread.

I think I will later post Aristotle vs. Galileo and gravity, for a little history spin on science.

[cdcox]

Originally Posted by prhom

See #437, because the treadmill can accelerate its not a static problem. It's a dynamics problem now, the extra force gets counteracted by some magical force propelling the treadmill to MATCH the speed of the wheel. It's tricky because the wheel and treadmill are by definition going the same speed as long as they are in contact with one another. So you can substitute matched speed with matched force. As soon as the plane starts to "speed up" relative to the treadmill the treadmill will respond with added speed from some magical engine that provides that forces. It's that external magical force that makes this a stupid question.

I stated many many posts ago that the problem is poorly stated.

I violated the statement of the problem (that the treadmill could match the wheel speed)

You violated Newton's second law (by postulating a magical force).

You can't satisfy both Newton's 2nd law and the problem statement in a natural system that doesn't mechanically fail.

[Pitt Gorilla]

It seems that the fundamental question/situation has changed. Are folks now suggesting that the treadmill is applying a force great enough to the wheels at an angle to counteract the force of the jet engines?

[Joe Seahawk]

Originally Posted by cdcox

No. There is something wrong with me for keep trying to come up with different explanations in an attempt to teach.

Where am I going wrong? if the treadmill moves at the backwards at the same speed the plane moves forward, I'm seeing the plane able to take off, although the wheels will be spinning twice as fast as non treadmill take off. I dunno, maybe I'm not understanding the question properly..

[cdcox]

Originally Posted by Pitt Gorilla

It seems that the fundamental question/situation has changed. Are folks now suggesting that the treadmill is applying a force great enough to the wheels at an angle to counteract the force of the jet engines?

I believe Orange is.

phrom is not.

[orange]

Originally Posted by Joe Seahawk

Where am I going wrong? if the treadmill moves at the backwards at the same speed the plane moves forward, I'm seeing the plane able to take off, although the wheels will be spinning twice as fast as non treadmill take off. I dunno, maybe I'm not understanding the question properly..

The plane isn't actually moving forward. When you say "the wheels will be spinning twice as fast," no. The speed of the treadmill equals the speed of the wheels.

Since the plane isn't moving forward, there's no lift.

[orange]

Originally Posted by Pitt Gorilla

It seems that the fundamental question/situation has changed. Are folks now suggesting that the treadmill is applying a force great enough to the wheels at an angle to counteract the force of the jet engines?

Originally Posted by cdcox

I believe Orange is.

phrom is not.

No. As I said just moments ago, the thrust doesn't have to be counteracted. The thrust is driving the treadmill. More thrust = faster treadmill. The treadmill is able to spin just as fast as necessary to keep up with the plane's wheels (which is also specified in the original problem).

[Pitt Gorilla]

Originally Posted by cdcox

I believe Orange is.

phrom is not.

If he's going to do that, why not just tether the plane to an immovable object directly behind it and define it as part of the treadmill.

[prhom]

I'm not postulating a magical force or changing the fundamental question. The original question says that the treadmill will ALWAYS match the speed of the plane's wheels. This means that the plane and the treadmill are in an escalating battle to out-accelerate each other. You guys are not taking into account the rotational acceleration of the wheels. That will consume ALL of the energy in the system so that there is nothing left to propel the plane forward. It's too simplistic to ignore that rotational acceleration.

[cdcox]

Originally Posted by Joe Seahawk

Where am I going wrong? if the treadmill moves at the backwards at the same speed the plane moves forward, I'm seeing the plane able to take off, although the wheels will be spinning twice as fast as non treadmill take off. I dunno, maybe I'm not understanding the question properly..

The problem statement (at least some versions of it) say the treadmill moves at the same rate as the wheels of the plane.

This statement causes a violation of Newton's second law.

[Joe Seahawk]

Originally Posted by orange

The plane isn't actually moving forward.

.

Why?

[Joe Seahawk]

Originally Posted by cdcox

The problem statement (at least some versions of it) say the treadmill moves at the same rate as the wheels of the plane.

This statement causes a violation of Newton's second law.

Ah..

[cdcox]

Originally Posted by orange

No. As I said just moments ago, the thrust doesn't have to be counteracted. The thrust is driving the treadmill. More thrust = faster treadmill. The treadmill is able to spin just as fast as necessary to keep up with the plane's wheels (which is also specified in the original problem).

Experimental verification please, for a vehicle in which the drive force is not imparted directly to the wheels. Rocket car works fine, but show me.

[orange]

Originally Posted by Pitt Gorilla

It seems that the fundamental question/situation has changed. Are folks now suggesting that the treadmill is applying a force great enough to the wheels at an angle to counteract the force of the jet engines?

I've suggested a variant that actually avoids the "motor on the treadmill will blow up" problem.

My posts and the responses to them are a bit off the beaten track (although I believe it may have become the beaten track, at least tonight).

[orange]

Originally Posted by cdcox

Experimental verification please, for a vehicle in which the drive force is not imparted directly to the wheels. Rocket car works fine, but show me.

Send me the money. All I need is the video recorder and the rocket engine - I can (generously) supply the rest.

Alternatively, you can try emailing my experiment to the Mythbusters guys, but will they ever read it? I think I have a better chance of getting a video recorder from you.

I WILL keep an eye out for something already online, though. Perhaps I can come up with a smarter search string than I've been using.

[prhom]

Originally Posted by Joe Seahawk

Where am I going wrong? if the treadmill moves at the backwards at the same speed the plane moves forward, I'm seeing the plane able to take off, although the wheels will be spinning twice as fast as non treadmill take off. I dunno, maybe I'm not understanding the question properly..

The plane wheels can never go faster than the treadmill because the original question said that the treadmill is designed to ALWAYS go as fast as the plane's wheels. Because of that statement we have to assume that as the plane accelerates and starts to gain on the treadmill, some control makes the treadmill accelerate and convert the plane's incremental thrust into ROTATIONAL acceleration and momentum in the wheels. By the way the problem is defined, the plane can never convert thrust into a higher incremental wheel speed versus the treadmill. THis has no basis in reality, and therefore cannot be proved by a simple experiment.
(At least it would require very complicated machinery to balance a model plane's thrust and treadmill acceleration)