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.

[orange]

Originally Posted by prhom

Well shit, I reread the original dumba$$ post from magic hef and I thought it said that the conveyor went a constant speed. It does not, it say "match the speed of the wheels", my bad orange. I should have re-read that question. As long as the conveyor has the ability to accelerate to match the wheels rotation then the plane won't take off. Sorry for all that trouble. Why didn't you just tell me to re-read the question?? I've just wasted an hour of my life. Dammit.

I feel this is warranted (not mocking, just celebrating):

[prhom]

Originally Posted by cdcox

Read the whole thread.

Ahh, whatever. I did read that part, just remembered it incorrectly. I'm still going to blame orange for not calling me on it earlier. By the way, he's right you know.

[cdcox]

Originally Posted by orange

Not in the rocket car in the mud - and you can extend it to a rocket car on the emissions rollers. All of the motive force on the plane/car MUST be transfered to the wheels or the plane/car will tip over.

That tow truck has a purchase. The jet's only purchase - wherever the jet engines are - is the wheels on the moving treadmill.

A rocket car starting out on top of card board on top of ice will not shoot the cardboard out from underneath the car while remaining stationary. Use a match box car, on an index card on butter, ice, wd-40 on formica, what ever. You cant move the index card backward without moving the match box forward.

[orange]

Originally Posted by prhom

Ahh, whatever. I did read that part, just remembered it incorrectly. I'm still going to blame orange for not calling me on it earlier. By the way, he's right you know.

Originally Posted by orange

I feel this is warranted (not mocking, just celebrating):

MAKE THAT A DOUBLE!

[cdcox]

Originally Posted by prhom

Ahh, whatever. I did read that part, just remembered it incorrectly. I'm still going to blame orange for not calling me on it earlier. By the way, he's right you know.

Not unless you believe

x = x + 5

or ignore newton's second law

or suppose that the bearings on the wheel have enormous friction that increases with rotational speed.

[cdcox]

Originally Posted by orange

MAKE THAT A DOUBLE!

Better save that until Baby Lee or headsnap say you are right.

[prhom]

Originally Posted by orange

I feel this is warranted (not mocking, just celebrating):

That's fine, but, it really doesn't make your arguments correct. The correct way to defend your position would have been to point out that the treadmill has an infinite capacity to accelerate and match the rotational speed of the plane's wheels. Don't focus on the equal and opposite forces, they are irrelevant. Well done for sticking with your opinion though.

[orange]

Originally Posted by cdcox

A rocket car starting out on top of card board on top of ice will not shoot the cardboard out from underneath the car while remaining stationary. Use a match box car, on an index card on butter, ice, wd-40 on formica, what ever. You cant move the index card backward without moving the match box forward.

None of these examples are close. I gave you good examples.

Originally Posted by cdcox

Not unless you believe

x = x + 5

or ignore newton's second law

or suppose that the bearings on the wheel have enormous friction that increases with rotational speed.

Originally Posted by orange

BUT my treadmill is every bit as frictionless as your bearings.

[cdcox]

Originally Posted by prhom

That's fine, but, it really doesn't make your arguments correct. The correct way to defend your position would have been to point out that the treadmill has an infinite capacity to accelerate and match the rotational speed of the plane's wheels. Don't focus on the equal and opposite forces, they are irrelevant. Well done for sticking with your opinion though.

You are falling into the trap of not understanding what the independent variable is:

speed of jet wheels (depends on) = speed of treadmill (set independently) + speed of jet (determined by force balance)

If you speed up the treadmill, you automatically speed up the jet wheels without affecting the speed of the jet, because the jet speed depends on the force balance, not on the speed of its wheels.

[prhom]

Originally Posted by cdcox

Not unless you believe

x = x + 5

or ignore newton's second law

or suppose that the bearings on the wheel have enormous friction that increases with rotational speed.

The original question says that the treadmill can exactly match the rotational speed of the wheels. If the treadmill is constantly accelerating to match the acceleration of the plane the wheels will just go faster. In real life the bearing will burn up pretty fast, but nothing about the durability of the bearings was stated.

[cdcox]

Originally Posted by orange

None of these examples are close. I gave you good examples.

Give me an example where the wheel that moves the drive shaft is not subjected to a motive force, like a drive shaft.

[cdcox]

Originally Posted by prhom

The original question says that the treadmill can exactly match the rotational speed of the wheels. If the treadmill is constantly accelerating to match the acceleration of the plane the wheels will just go faster. In real life the bearing will burn up pretty fast, but nothing about the durability of the bearings was stated.

Now you are depending on the bearing burning up and seizing in order to keep the jet from taking off. I think that violates the spirit of the brain teaser.

[orange]

Originally Posted by cdcox

You are falling into the trap of not understanding what the independent variable is:

speed of jet wheels (depends on) = speed of treadmill (set independently) + speed of jet (determined by force balance)

speed of jet wheels (depends on) - speed of treadmill (equals wheel speed) =
speed of treadmill (equals wheel speed) + speed of jet (determined by force balance) - speed of treadmill (equals wheel speed)

speed of jet wheels (depends on) - speed of treadmill (equals wheel speed) =
speed of treadmill (equals wheel speed) + speed of jet (determined by force balance) - speed of treadmill (equals wheel speed)


0 = speed of jet (determined by force balance)

[prhom]

Originally Posted by cdcox

You are falling into the trap of not understanding what the independent variable is:

speed of jet wheels (depends on) = speed of treadmill (set independently) + speed of jet (determined by force balance)

If you speed up the treadmill, you automatically speed up the jet wheels without affecting the speed of the jet, because the jet speed depends on the force balance, not on the speed of its wheels.

I'm going to bed after this because frankly, I'm exhausted now. Since the treadmill has an unlimited capacity to accelerate it could theoretically continue accelerating until the friction in the wheel bearings was greater than the acceleration force of the plane. Again, in the real world everything would burn up in this ridiculous scenario pretty fast.

[orange]

Originally Posted by cdcox

Give me an example where the wheel that moves the drive shaft is not subjected to a motive force, like a drive shaft.

The rocket cars. Already mentioned.