# One More Teaser



## CamperAndy (Aug 26, 2004)

Okay, get a couple of tubes 20 feet long and stand them beside a building. The tubes are just big enough to fit a bowling ball.

Cap the ends with a bowling ball in one tube and a feather in the other. Now pull an absolute vacuum in the tubes. The feather and ball are held at the top.

When released at exactly the same moment which hits the bottom of the tube first????


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## Thor (Apr 7, 2004)

Feather.

Both will want to fall at the same rate; however the tube is the exact size of the ball (there will be friction between the ball and the tube). The feather is smaller and will not rub on the sides of the tube.

Thor


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## Reverie (Aug 9, 2004)

Thor is right. Now, if the tube was even a millimeter larger in diameter than the bowling ball both the ball and the feathers would fall at the exact same rate. Of course you are assuming that the tube is absolutely vertical and the ball is falling absolutely vertical. If you introduced atmosphere into the tubes it would change the rate of fall quite a bit.

Reverie


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## HootBob (Apr 26, 2004)

Good answer Thor








I go with Thor's answer









Don


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## OutbackPM (Sep 14, 2005)

For those of us who are old enough to remember when they did this experiment on the moon. I think it was a hammer and a feather that one of the astronaughts dropped to show they all fall at the same rate.

In this case I believe Thor has it right and only the friction will slow the ball if it were touching.

David


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## bill_pfaff (Mar 11, 2005)

Well now says me.

If you want to get technical, (friction aspect aside, albeit a good one), the bowling ball will hit first assuming that the starting line is on center of the two objects.

This is because the mere volume of the ball is more than the feather and so the balls bottom is by design closer to the end of the tube.

This can be illustrated with an â€œOâ€ for the bowling ball and a â€œ-â€œ for the feather:

"O-"

As you can see the bottom of the ball protrudes beyond the feather.

oooooooooooh they say!

Just being a pain in the ....

Bill


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## tdvffjohn (Mar 10, 2005)

All I know even if they fall at the same rate of speed I will catch the feather not the ball!


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## cookie9933 (Feb 26, 2005)

bill_pfaff said:


> This is because the mere volume of the ball is more than the feather and so the balls bottom is by design closer to the end of the tube.
> 
> As you can see the bottom of the ball protrudes beyond the feather.
> 
> ...


Don't know that this teaser is meant to be a trick. I would assume that the ball's and feather's lowest points are equal, so that they both get a fair start.

Now if the tube's I.D. and the ball's O.D. are exactly equal, the ball would probably not move at all, assuming that neither ball or tube deform.

If the ball has any clearance and the tube is vertical, I say the feather will win due to the impulse owing to the ball's mass.

How about it, Andy?

Bill


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## Paul_in_Ohio (Sep 29, 2004)

What weighs more...

A ton of feathers or a ton of bowling balls????


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## CamperAndy (Aug 26, 2004)

You guys tightened up the tube a bit on me as there is two more parts to this problem. More to follow as you guys work it out.

To add a bit of clarity. The ball is perfectly round as is the tube and there is plenty of clearence that the ball does not touch on the way down. The feather and the ball are both starting at the same bottom point and just so we keep everything grounded this is all happening on Earth.


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## mswalt (Sep 14, 2004)

CamperAndy,



> just so we keep everything grounded this is all happening on Earth.


Northern Hemisphere or Southern? Nightime or daytime? I also need the exact longitude and lattiude, please.

Thanks,

Mark


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## PDX_Doug (Nov 16, 2004)

This is a good one Andy!









Of course, the basis of this is found in one of the classic Physics 101 lessons. That is objects fall at the same rate regardless of the weight. So in that light they will both reach the bottom at the same time.

I think it is fair to discount the friction factor and the fact the the bowling ball is taller than the feather, thus giving it a 'head start'. These only complicate the issue.

There is another factor that I am not clear on though. When you 'pull the vacuum', are you saying that you are using the vacuum to 'suck' the items to the top of the tube? If so, with a close enough clearance the ball would rise, but not the feather. In any case, if this were true, and the there is air below the ball, we would have to figure in the compression of that air below, which would slow the fall of the ball, possiblly even stopping it before it hit ground.

Or, is the vacuum comlete in the entire tube, with the purpose of the vacuum being to eliminate air compression as a factor? If this is the case - and I'm guessing it is - I will say that both the bowling ball and the feather will hit the ground at the same time.

Happy Trails,
Doug


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## GenesRUs (Oct 11, 2004)

I wasn't going to way in on any of the teasers, but...
I have a Ph.D. in molecular biology, biochemistry and biophysics, and am currently a tenured professor with the University of Colorado. Been a federally funded scientist for allmost 15 years, published over 50 peer-reviewed articles, and also serve as a consultant to the National Institutes of Health and on professional journal editorial boards. I'm not a physist, but I sat through 12 semesters of various physics course, got good grades, and use the principles and equations of physics in my daily work. So here goes....

Airplane teaser:
Airplanes take off from the lift supplied by air moving across the wing surfaces. Movement of the aircraft is supplied from engine thrust, but the engines do not provide lift themselves. So, principle 1: movement of plane = movement of air over wing = lift = take off. Therefore, no movement = no take off.
If the moving runway is moving in the same direction as the rotation of the plane's wheels at an equal velocity, then the plane remains motionless with respect to the air. No matter how much thrust is applied by the engines, the plane does not nove forward because the intended forward rotation of the wheels is compensated for by the rearward motion of the moving runway. So, appying principle number 1, no motion = no takeoff.
If the runway moves opposite the motion of the wheels, and the coefficient of friction between the wheels and the runway is sufficiently high to prevent decohesion of the wheels and the runway surface, then the wheels cannot move because any forward rolling motion of the wheels would be negated by an opposing force from opposite movement of the runway. Again, from principle 1, no motion = no take off.

Helium balloon teaser:
If think we can assume that the car, occupants and balloon are traveling at constant velocity before the turn is initiated. Then the principle of inertia applies - bodies at rest remain at rest unless acted upon by an outside force. Likewise, a body in constant velocity motion will retain that motion unless acted upon by an outside force. So, if a car traveling at constant velocity makes a turn to the left, the car body, the occupants, and the balloon all momentarily continue to travel in the direction of the original motion, that is to the right or the outside of the turn untll the force of the turn is fully transmitted to them.

Bowling ball/feather teaser:
Principle - if unaffected by other forces, bodies will undergo equal acceleration in a gravitional field independent of their mass. So, if you drop a bowling ball and a feather in a vacuum from the same point, both hit the ground a the same time.
However, the tubes and external air pressure introduce additional variables, which are difficult to account for. The external air pressure would add an extra force to both the ball and the feather. If we assume that the gap between the ball and the inner surface of the tube are small enough to prevent "blow-by" of the air, then the external air pressure would supply a tremendous accelerative force to the ball. It's difficult to imagine that the air outside the tube would not blow past or through the feather, decreasing the force appllied by the atmosphere. Likewise, because of the complex shape of the feather, its path through the tube would be affected by turbulence. Given these considerations, and negating the affects of contact between the ball and the tube, the ball would probably hit the ground first.

If you want the force diagrams and equations for any of the teaser, let me know (although it might take a while to get back to ya 'cause my wife's honey-do list has much higher priority).

Have fun!


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## Crawfish (Sep 14, 2005)

"Elementarity my dear Andy, elementarity.

I'm with Doug.

"*Let's Go Camping*"

Crawfish


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## Moosegut (Sep 24, 2005)

GenesRUs said:


> I wasn't going to way in on any of the teasers, but...
> I have a Ph.D. in molecular biology, biochemistry and biophysics, and am currently a tenured professor with the University of Colorado. Been a federally funded scientist for allmost 15 years, published over 50 peer-reviewed articles, and also serve as a consultant to the National Institutes of Health and on professional journal editorial boards. I'm not a physist, but I sat through 12 semesters of various physics course, got good grades, and use the principles and equations of physics in my daily work. [snapback]66439[/snapback]​


See!!!??? I was right! I agree with everything this guy just said.


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## tdvffjohn (Mar 10, 2005)

GenesRus, all that education and an explanation I was able to understand! You are The Man.









John


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## Moosegut (Sep 24, 2005)

Not really. I disagree about the plane.


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## Moosegut (Sep 24, 2005)

Moosegut said:


> Not really. I disagree about the plane.
> 
> 
> 
> ...


And here's why - For every "action" (Hey! It wouldn't let me spell 'action - I had to put in quotes so the emoticon wouldn't show up.) there is an equal and opposite reaction. The thrust of the engines propels the plane forward irrespective of what the wheels and the conveyor belt are doing. The belt does not LOCK the wheels in place. The belt allows the wheels to turn. Calculate the forward motion of the plane into the wheel speed and all you have to do is crank up the speed of the conveyor belt to match it. This is, of course, coming from a fourth grade level of understanding of math and physics.









Scott


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## Fire44 (Mar 6, 2005)

I think we should walk across the street from the building with the two tubes.....
Go into the bar sit at a window seat, have a cold beverage and watch the ball and feather drop.........

Gary


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## PDX_Doug (Nov 16, 2004)

I don't know Gary...

I like your idea, but if we start introducing alcohol into these equations, things could get really ugly!









GenesRUs,

I don't know what to say here. I have great respect for your level of education and intelligence, but in the immortal words of the late Carl Sagan, Phd...

"All the intelligence in the world, is no guarantee against being dead wrong."

Just ask Copernicus!









Happy Trails,
Doug


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## CamperAndy (Aug 26, 2004)

Well some have it and some don't.

Since there is no air or anything else for that matter in an absolute vacuum in the tube there will be no resistance no matter the shape of the object and both will drop at a constant acceleration of 32.15 f/s/s no matter what the mass of the object is.

Thus they will hit bottom at the same time.

Now lets add normal air and change the tube size to say 12 inches bigger then the bowling ball.

Dropping them in these conditions which would hit bottom first?


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## PDX_Doug (Nov 16, 2004)

The rate the feather and the bowling ball will fall through the the atmosphere is dependant on a number of factors about each we do not know (weight, 'frontal area', air density, etc.).

The quick answer is that the feather with it's small mass and relatively large frontal area will reach it's terminal velocity much sooner, and it will be at a much slower speed. The bowling ball, with it's much greater mass, will need to achieve a much higher speed before the attendant aerodynamic drag matches its weight, and it achieves terminal velocity.

Without knowing the specific numbers on these two objects, we cannot say with absolute certainty, but one can speculate that even in as little as a twenty foot drop, aerodynamic drag will be having a much greater effect on the feather, and it will be much closer to reaching it's slower terminal velocity, than the bowling ball which will be continuing to accelerate virtually unabated at that point.

Based on what we know at this time... The Bowling ball will hit ground first.

And you can blame Sir Issac Newton for all of that!









Happy Trails,
Doug

P.S.: Let me guess Andy, the next step will be to remove the tubes and add a cross wind component. Have you always been such a sadist!


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## Steelhead (Nov 14, 2005)

I agree with GenesRUs in his analysis of the first two problems. He is right on. As for the bowling ball and feather a few facts are needed. Is it a chicken feather, goose feather or peacock feather? What material is the bowling ball made from? what is the dimensional tolerance of the ball's radius? and, are the tubes made of ultra high molecular weight polyethelyne? if you can answer these then the resolution of your problem will be intuitively obvious









Dallas


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## GenesRUs (Oct 11, 2004)

Hi again guy and gals:

Let me begin by apologizing for being overzealous in selling my own credentials. I really only intended to convey that I had some experience with problems like this, not an all-knowing expert. Forgiveness please?

The airplane teaser remains a point of contention. Let's look at it by analogy. Suppose we have a hang glider attached to an olympic athlete. The athlete is capable of running fast enough on solid ground that the movement of air over the hang glider wings is sufficient to provide lift for take off. Like the airplane, the athletes legs provide thrust for forward movement, but not lift. And, like the plane, forward motion = lift = take off.
Ok, so now we put the athlete and hang glider on a tread mill. No matter how fast the athlete runs, he remains stationary due to the rearward motion of the tread mill. No forward movement = no lift = no take off. 
Likewise, if the athlete simply runs in place, there will be no take-off because there is no forward motion to produce lift. Forward motion to provide lift is the key.

MooseGut made an interesting point about - for every action, there is an equal and opposite reaction! Excellent point. That's why rockets can fly in the near vacuum of outer space. The thrust of the rocket (even in a vacuum)- the action- results in an equal and opposite reaction - forward motion of the rocket. That's the same with airplanes, too. The engine thrust, even with nothing but air to "push against" results in the opposite reaction - forward plane motion. So, how does this apply to the teaser?
Well, the plane engines provide thrust for motion. In order to take off the plane must overcome friction which is normally accomplished by forward rolling of the wheels. But, in the teaser, wheel rolling is exactly counteracted by the rearward travel of the run way. Yes, there is an equal and opposite reaction to the engine thrust - the plane is trying to move forward - but it can't because of the compensatory motion of the runway. No forward motion = no lift no take off. in effect, the energy expended by the engines is "wasted" or lost to the rearward travel of the runway.

At least that's how I (very humbly) see it. If you can explain where my error is being made, please, please tell me! I may be an old dog, but I can still learn a few new tricks.

GenesRUs


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## PDX_Doug (Nov 16, 2004)

Genes,



GenesRUs said:


> Let me begin by apologizing for being overzealous in selling my own credentials. I really only intended to convey that I had some experience with problems like this, not an all-knowing expert. Forgiveness please?


I hope that was not in response to the comment I made.







I had no intention of lobbing a personal attack. It was simply a quote that has always stuck with me, and reminds me not to automatically mistake credentials for fact. I apologize if it came off wrong. BTW, considering the scope of these discussions we have been having, appropriate credentials are a valuable factor in your argument.



GenesRUs said:


> Like the airplane, the athletes legs provide thrust for forward movement, but not lift. And, like the plane, forward motion = lift = take off.


I still believe, as I have stated earlier, that there is a fundamental difference in this example, vs. the airplane in question. In the example of the athelete on the treadmill, the forward thrust is the result of a direct mechanical connection between the runners legs and the treadmill belt. All power is transfered through that connection and is affected by both.

The forward thrust of the airplane however is entirely independent of the connection between the wheels and the runway. If it were not, the airplane would not be able to maintain flight once airborne, and as we all now, they usually do! As such I do not agree that this is a valid analogy.



GenesRUs said:


> Ok, so now we put the athlete and hang glider on a tread mill. No matter how fast the athlete runs, he remains stationary due to the rearward motion of the tread mill. No forward movement = no lift = no take off.


This goes back to an argument I presented earlier, in order to stop the rotation of the wheels, the runway belt does not move rearward (that would double the rotational speed of the wheels), but forward to apply an equal counter-rotational force to the wheels and cause them to stop. If we can get our minds wrapped around this, it is easy to see that the moving runway will not stop the aircraft from moving through the air, but move along with it.

Think about it...

Happy Trails,
Doug


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## Moosegut (Sep 24, 2005)

Ya know . . . The physics teacher (PHD) *HAS* to get married over the Thanksgiving weekend and go on his honeymoon this weeK!!!! Just when I need him!


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## 2500Ram (Oct 30, 2005)

I thought we were over the plane









As my simple mind see's it. Obviously the wheels are not producing any forward momentum or thrust. The belt is moving in the opposite direction of the foreword movement of the plane equal to the movement of the â€œwheelsâ€

So in my simple mind, why canâ€™t the wheels be spinning at 200mph with the track spinning at 200mph in the opposite direction and the plane not be moving forward? The wheels and belt have nothing to do with the engine of the plane. As the plane engine picks up speed the belt and plane wheels also pickup speed. This all comes back to the belt wouldnâ€™t be moving IF the plane wasnâ€™t going foreword. No movement on the wheels no movement on the belt. There is nothing holding the plane on the ground soâ€¦

Bill.


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## CamperAndy (Aug 26, 2004)

One good thing about these is they get your post count up.

Guys the engines push the plane forward because of thrust against the air. The only reason the wheels are spinning is not the tread mill but the fact that the plane is actually moving. If the plane was not moving then the tread mill would have nothing to do.

You know we could send this to Myth Busters and see what they say.


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## 2500Ram (Oct 30, 2005)

CamperAndy said:


> You know we could send this to Myth Busters and see what they say.
> [snapback]66496[/snapback]​


Funny I was thinking that today as well, but how could you actually recreate this. It would have to be models and there would still be debate because it wasn't real









Oh ya, post count up by 1









Bill.


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## Thor (Apr 7, 2004)

PDX

The ball and the feather are in a vacuum. There is no drag.

On the moon - no air (like a vacuum) the ball and the feather will fall at the same rate. The only force is gravity. On earth g = 9.81 m/s2 regardless of feather or ball. The force which slows a falling object is friction cause by the air moving around the object. (shape, size, play factor). eliminate the froce the rate is the same.

I guess the basic assumption is that the ball start on the same staring line not relative to there center of mass.

Thor


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## PDX_Doug (Nov 16, 2004)

Thor said:


> PDX
> 
> The ball and the feather are in a vacuum. There is no drag.


Thor,

Read Andy's post just before the post of mine that I discuss drag in. He has changed the ball game on us, and removed the vacuum component from the equation. My post was in response to that revised question.

Otherwise, you are right, in a vacuum they fall together, at the same rate. I believe you will also see me agreeing with that in my first post on this thread.









Happy Trails,
Doug


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## Moosegut (Sep 24, 2005)

GenesRUs said:


> That's why rockets can fly in the near vacuum of outer space.Â The thrust of the rocket (even in a vacuum)- the action- results in an equal and opposite reaction - forward motion of the rocket.Â That's the same with airplanes, too.Â The engine thrust, even with nothing but air to "push against" results in the opposite reaction - forward plane motion.Â
> 
> GenesRUs
> [snapback]66477[/snapback]​


GenesRUs,

I'm not trying to prove MY point here, I'm just trying to understand it. Based upon what you said about the rocket in space, if the rocket had wheels that were on a converyor belt floating in space, it would not move. My contention is, it would move and the wheels and conveyor belt would just gain speed based upon that movement.

If the wheels were motorized and moved at ten miles per hour, the conveyor belt would move at ten miles per hour. BUT, if the wheel motors continue to turn the wheels at ten MPH and you cause that plane to move forward (whether by prop, jet, or rocket engine - or a giant hand pushing it forward for that matter) at a rate of five miles per hour, then the wheels and conveyor belt just have to speed up to 15 MPH in their respective directions. But the plane still moves forward.

And until the physics teacher gets back from his honeymoon, I aint budging.









Scott

P.S. Sorry for talking about the plane while we're in the tube.


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## nascarcamper (Jan 27, 2005)

Here's the easy solution to find out which hits first. Take your shoes off and stand on a firm surface. Make sure the air temperature is at least 30 degrees or less. Stay in this postion for a minimum of 15 minutes then drop the bowling ball on your left foot and the feather on the right. If your right eye starts watering first it's the bowling ball.


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## Thor (Apr 7, 2004)

GenesRUs

I am going to have to disagree with you.

A prop plane will not move forward in space. (assuming the engine will run) The prop pushes/pulls air to move forward, that is why there is a pitch to the prop. If the prop was a disc the plane would not move forward. A plane in space would actually start to rotate in the opposite direction of the engine. No air in space to forward motion. Kinda like a helicopter without the rear prop.

A jet requires air as well to provide thrust (a jet engine works this way) again no motion in space.

Now rocket engine does no require air for thrust hence motion. The force of the gas exiting the rocket pushes the rocket forward.

PDX

No fair, the game has changed rules half way through. I guess I should read a bit better







- We agree on something









Thor


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