Science Something amazing to tell you concerning physics and motion - Page 13

Jenson71 · 06-04-2009, 10:15 AM

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** · 06-04-2009, 02:34 PM

Quote:

Originally Posted by orange

So you're building a critical flaw into the test. Way to get the answer you want.

Perfect rolling = no slippage

Perfect rolling = pure slippage.

Sully · 06-04-2009, 02:35 PM

I'm not a physics guy, and once someone's posts go into more than about 15 words or start using formulas, I go into a brief coma.

However, this treadmill thing sound impossible. Once the jet kicks in, there must be forward movement for the wheels to even begin to move against this imaginary treadmill...meaning there will always be forward movement.

Am I wrong?

**Buck** · 06-04-2009, 02:37 PM

So since the wheels on the plane are going the same speed traveling forward as the rest of the plane, 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 speed of the plane, moving in the opposite direction. Can the plane take off?

I changed the word Wheels to Plane.

Thats the real question I guess.

MagicHef · 06-04-2009, 02:38 PM

Quote:

Originally Posted by Sully

I'm not a physics guy, and once someone's posts go into more than about 15 words or start using formulas, I go into a brief coma.

However, this treadmill thing sound impossible. Once the jet kicks in, there must be forward movement for the wheels to even begin to move against this imaginary treadmill...meaning there will always be forward movement.

Am I wrong?

Of course it's impossible. That's not the point.

orange · 06-04-2009, 02:39 PM

Quote:

Originally Posted by cdcox

Perfect rolling = pure slippage.

I'm not sure how you're using the word. Let me give you my understanding.

Circumference of wheel = 1
Circumference of treadmill = 1

Ideal (1.0) roll of wheel produces (1.0) roll of treadmill
Non-ideal (1.0) roll of wheel produces (1.0 - x) roll of treadmill; x = slippage

bdeg · 06-04-2009, 02:40 PM

Quote:

Originally Posted by MagicHef

Who said that?

the wheel

MagicHef · 06-04-2009, 02:40 PM

Quote:

Originally Posted by cdcox

Let's try once more from physics.

The plane is initially at zero velocity. To start moving, it needs to accelerate. The acceleration of the plane a = F/m where F is the force and m is the mass of the plane.

The jet engines are one source of force. They push on the air. It is what makes a normal plane move forward.

To keep velocity zero, we need to keep acceleration zero. In order to do that we need a force that opposes the jet engine. The only place it can come from is the tread mill. The tread mill transmits it's force to the wheel and the wheel to the bearing. If the bearing were frictionless, there would be no force on the airplane from this spinning wheel. But in real life, there is friction. The friction would impart a force something like friction force = m*g*k where k is a friction coefficient. Regardless the friction force is small relative to the force of the jet engines. If it were not, the plane couldn't roll in the first place. The velocity of the wheel has very little to do with the amount of friction in the bearing. You can't spin the wheels fast enough to keep the plane stationary by generating more friction at the wheel. It is like the example of a person holding on to the tow rope.

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.

**cdcox** · 06-04-2009, 02:40 PM

Actual wheels could not be spun fast enough to generate enough friction to overcome the thrust of jet engines.

Sully · 06-04-2009, 02:41 PM

Quote:

Originally Posted by MagicHef

Of course it's impossible. That's not the point.

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

MagicHef · 06-04-2009, 02:42 PM

Quote:

Originally Posted by MediaCenterJunkie

So since the wheels on the plane are going the same speed traveling forward as the rest of the plane, 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 speed of the plane, moving in the opposite direction. Can the plane take off?

I changed the word Wheels to Plane.

Thats the real question I guess.

No, the wheels can be moving at 5 ft/sec with the treadmill moving at 5 ft/sec in the opposite direction, and the plane will be moving at 0 ft/sec.

MagicHef · 06-04-2009, 02:42 PM

Quote:

Originally Posted by cdcox

Actual wheels could not be spun fast enough to generate enough friction to overcome the thrust of jet engines.

That is true.

orange · 06-04-2009, 02:43 PM

Quote:

Originally Posted by MediaCenterJunkie

So since the wheels on the plane are going the same speed traveling forward as the rest of the plane, 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 speed of the plane, moving in the opposite direction. Can the plane take off?

I changed the word Wheels to Plane.

Thats the real question I guess.

The net speed (plane plus conveyor belt) must equal 0.

The plane will never move forward, there will be no lift generated and it won't take off.

MagicHef · 06-04-2009, 02:43 PM

Quote:

Originally Posted by bdeg

the wheel

The wheel said nothing about being frictionless.

**Buck** · 06-04-2009, 02:43 PM

Quote:

Originally Posted by MagicHef

No, the wheels can be moving at 5 ft/sec with the treadmill moving at 5 ft/sec in the opposite direction, and the plane will be moving at 0 ft/sec.

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.

orange · 06-04-2009, 02:44 PM

Quote:

Originally Posted by Sully

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

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

06-04-2009, 10:15 AM
Jenson71 fides quaerens intellectum Join Date: Oct 2003 Location: United States Casino cash: $8330900	Something amazing to tell you concerning physics and motion 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.
Posts: 15,986

06-04-2009, 02:35 PM	#182
Sully It Goes On Join Date: Sep 2005 Location: Lees Summit Casino cash: $10026331	I'm not a physics guy, and once someone's posts go into more than about 15 words or start using formulas, I go into a brief coma. However, this treadmill thing sound impossible. Once the jet kicks in, there must be forward movement for the wheels to even begin to move against this imaginary treadmill...meaning there will always be forward movement. Am I wrong? __________________ "And I don't wish that girl any bad luck," he said, "but I hope she gets hit with a car." - Tommy Lasorda
Posts: 18,295

06-04-2009, 02:37 PM	#183
Buck Take a Chill Pill Join Date: Nov 2006 Location: South Carolina Casino cash: $6180295	So since the wheels on the plane are going the same speed traveling forward as the rest of the plane, 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 speed of the plane, moving in the opposite direction. Can the plane take off? I changed the word Wheels to Plane. Thats the real question I guess.
Posts: 44,604

06-04-2009, 02:40 PM	#188
cdcox www.nfl-forecast.com Join Date: Sep 2000 Casino cash: $-478231	Actual wheels could not be spun fast enough to generate enough friction to overcome the thrust of jet engines.
Posts: 46,032