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 MediaCenterJunkie

The wheels dont affect the plane moving, so the real question is if the treadmill is going the same speed as the plane, not the wheels.

Extrapolate from my answer in #185. As the wheel rotates, the plane's hypothetical forward speed equals circumference/(time/rotation); the conveyor belt's speed must equal this.

[MagicHef]

Originally Posted by MediaCenterJunkie

The wheels dont affect the plane moving, so the real question is if the treadmill is going the same speed as the plane, not the wheels.

The wheels are solidly attached to the plane, so they affect the motion of the plane in the sense that the speed of the plane in relation to the speed of the treadmill will always be equal to the speed of the wheels.

[Simply Red]

MagicHef sure knows his 'Physics'

Sick 'EM, BOY!!!

[Sully]

Originally Posted by orange

No. Ideally the wheel only has move forward one point (0 distance) to start rolling.

So at some point the wheels are moving faster than the treadmill? And the treadmill must catch up?

[Baby Lee]

Originally Posted by orange

Except for one critical difference - you're NOT airborne. Where did you get the initial lift to get off the ground?

There are two COMPLETELY DISTINCT STATES. Plane sitting on ground - plane moving in air.

With frictionless wheel bearings, the only function of the wheels on the conveyor is to provide a normal force separating the plane from the ground by the width of the tires. In all other respects this situation is identical to flying with the landing gear extended.

And is also identical to a pontoon plane on water, or a ski plane on ice.
The lift comes from the rearward thrust pushing the plane body forward as it 'skates' on the conveyor surface.

[Buck]

Originally Posted by MagicHef

The wheels are solidly attached to the plane, so they affect the motion of the plane in the sense that the speed of the plane in relation to the speed of the treadmill will always be equal to the speed of the wheels.

If the plane isn't moving forward relative to the ground, then its speed is 0, meaning the treadmill's speed is also 0, but that cannot be the case. The speed of the wheels in the original question was referring to the speed in which they were spinning.

Am I wrong here?

[orange]

Originally Posted by Sully

So at some point the wheels are moving faster than the treadmill? And the treadmill must catch up?

No. Let's say the wheel starts out with point A in contact with treadmill point X. The next instant wheel point A+1 makes contact with treadmill point X+1. Both are in simultaneous motion, both bits are driven back to position A and X.

[MagicHef]

Originally Posted by MediaCenterJunkie

If the plane isn't moving forward relative to the ground, then its speed is 0, meaning the treadmill's speed is also 0, but that cannot be the case. The speed of the wheels in the original question was referring to the speed in which they were spinning.

Am I wrong here?

The plane's speed has no effect on the treadmill's speed.

[orange]

Originally Posted by Baby Lee

And is also identical to a pontoon plane on water, or a ski plane on ice.
The lift comes from the rearward thrust pushing the plane body forward as it 'skates' on the conveyor surface.

The plane is only 'skating' relative to the conveyor surface - which is also 'skating' at equal and opposite speed. Neither water nor ice is a perfect treadmill (certainly not ice which doesn't move at all - ski plane on ice relies on relatively frictionless contact with "the ground").

The plane is NOT moving forward relative to the atmosphere and produces no lift.

Motion is relative, remember?

Originally Posted by MediaCenterJunkie

If the plane isn't moving forward relative to the ground, then its speed is 0, meaning the treadmill's speed is also 0, but that cannot be the case. The speed of the wheels in the original question was referring to the speed in which they were spinning.

Am I wrong here?

The "plane" INCLUDES the wheels. The wheels are moving. That's where all the energy is going. Spinning the wheels. The wheels are resisted by friction against the treadmill. The treadmill absorbs that energy and moves in the opposite direction.

[Sully]

Originally Posted by orange

No. Let's say the wheel starts out with point A in contact with treadmill point X. The next instant wheel point A+1 makes contact with treadmill point X+1. Both are in simultaneous motion, both bits are driven back to position A and X.

What makes the treadmill begin to move?

[cdcox]

Originally Posted by MagicHef

In approximations pertaining to ideal friction, velocity has nothing to do with frictional force. Explain to me how the plane moves if the parameters of the question hold.

I think this problem is set up with an impossible tautology, just like my rollerskate, moving sidewalk, and tow rope example. You cannot match the speed of the wheels and the conveyor belt because the speed of the airplane is externally set. I believe the author of the problem has done this intentionally to get people to talk past one another.

I will defend this to the end of time:

Put a jet on a tread mill. Once the jet starts rolling, run the tread mill at any real speed and direction (it hast to be a real speed, but even 500 mph would be okay). The jet will take off.

[MagicHef]

Originally Posted by Sully

I'm just saying, niether the wheel nor the treadmill would ever move in this scenario...right?

Theoretically, no, unless someone came up and pushed on the treadmill or something.

[Buck]

Originally Posted by MagicHef

The plane's speed has no effect on the treadmill's speed.

Ok, am going to word this differently, again.

The planes wheel's clearly have 2 different speeds. The speed in which the plane is moving forward, which I'm going to label as its static speed, and the speed in which the wheels are spinning, which I'm going to call their rotating speed.

If the question is

Imagine a 747 is sitting on a conveyor belt, as wide and long as a runway. The conveyor belt is designed to exactly match the static speed of the plane (you can substitute the word wheels for plane here because the wheels, as part of the plane have the same static speed of the plane), moving in the opposite direction. Can the plane take off?

then you have a case.

If the question is

Imagine a 747 is sitting on a conveyor belt, as wide and long as a runway. The conveyor belt is designed to exactly match the rotating speed of the wheels, moving in the opposite direction. Can the plane take off?

then, you have no case, because the rotating speed of the wheels has no affect on whether or not the plane can move forward or take off.

[nstygma]

LOL
i just read a comment here about the plane crash in the ocean near Brazil. Which one of you posted it? reerun?

I love all the so-called "experts" on this thread stating what they call "facts" when they weren't even there. I've been a pilot for 47 years and I've been in this same situation at least 100 times. The first thing you learn in flight school (and trust me, this has saved me every time) is that right before you hit the ground, you jump up fast enough to counteract the descending speed. IMHO, these people just weren't paying attention.

[Baby Lee]

Originally Posted by cdcox

You cannot match the speed of the wheels and the conveyor belt because the speed of the airplane is externally set.

That's perhaps the most succinct way of putting it exactly right.

As the thrust comes from the jets exerting force on the air behind, everything concerning the wheels and conveyor are just variations on what happens to molecules in the atmosphere as the jet flys by, or molecules in a lake or ice slab as a pontoon or ski plane takes off.