A little physics brain teaser to drive you crazy.

[dug777]

Originally posted by: Fenixgoon
AND I HAVE A PHYSICS PROBLEM FOR YOU!

if a plane is on a conveyor belt style runway, and the rate at which the surface of the belt moves is always equal to the velocity of the airplane, will the plane ever take off?

only if it is alternator shaped.

 

[Born2bwire]

Originally posted by: Fenixgoon
AND I HAVE A PHYSICS PROBLEM FOR YOU!

if a plane is on a conveyor belt style runway, and the rate at which the surface of the belt moves is always equal to the velocity of the airplane, will the plane ever take off?

Haha, that thread still makes me cry.

 

[Special K]

The original problem sounds like some variation of Zeno's Paradox.

 

[SVT Cobra]

Originally posted by: Fenixgoon
AND I HAVE A PHYSICS PROBLEM FOR YOU!

if a plane is on a conveyor belt style runway, and the rate at which the surface of the belt moves is always equal to the velocity of the airplane, will the plane ever take off?

No, the displacement is 0 relative to the air.

 

[OSX]

There is no spoon.

 

[DrPizza]

I worked on a similar problem on about 2 dozen napkins during a lunch with half a dozen physics profs... If a hole were drilled through the center of the earth, and an object was dropped into the hole, would it ever reach the center of the earth?

edit: and I better point out that I did NOT say, "ignoring air resistance."
Plus, we'll drill from the N-pole to the S-pole to minimize problems with the coreolis effect.

 

[TheoPetro]

Originally posted by: DrPizza
I worked on a similar problem on about 2 dozen napkins during a lunch with half a dozen physics profs... If a hole were drilled through the center of the earth, and an object was dropped into the hole, would it ever reach the center of the earth?

edit: and I better point out that I did NOT say, "ignoring air resistance."
Plus, we'll drill from the N-pole to the S-pole to minimize problems with the coreolis effect.

Does it not because of the whole /(r^2) in the gravity equation? Kinda hard to divide by 0.

 

[silverpig]

Originally posted by: DrPizza
I worked on a similar problem on about 2 dozen napkins during a lunch with half a dozen physics profs... If a hole were drilled through the center of the earth, and an object was dropped into the hole, would it ever reach the center of the earth?

edit: and I better point out that I did NOT say, "ignoring air resistance."
Plus, we'll drill from the N-pole to the S-pole to minimize problems with the coreolis effect.

I'm going to guess no right here because if you consider a 6500km high column of gravitationally supported air, my guess is that near the bottom the pressure would be so great as to liquify the air at least in part.

 

[silverpig]

Originally posted by: TheoPetro

Originally posted by: DrPizza
I worked on a similar problem on about 2 dozen napkins during a lunch with half a dozen physics profs... If a hole were drilled through the center of the earth, and an object was dropped into the hole, would it ever reach the center of the earth?

edit: and I better point out that I did NOT say, "ignoring air resistance."
Plus, we'll drill from the N-pole to the S-pole to minimize problems with the coreolis effect.

Does it not because of the whole /(r^2) in the gravity equation? Kinda hard to divide by 0.

That's not the right way to consider the problem. If you went straight with 1/r^2 your gravitational force would be extremely strong near the center of the earth. Now, while it is true that you are the deepest in the earth's gravitational potential there, the net force you would feel is zero.

 

[TheoPetro]

Originally posted by: silverpig

Originally posted by: TheoPetro

Originally posted by: DrPizza
I worked on a similar problem on about 2 dozen napkins during a lunch with half a dozen physics profs... If a hole were drilled through the center of the earth, and an object was dropped into the hole, would it ever reach the center of the earth?

edit: and I better point out that I did NOT say, "ignoring air resistance."
Plus, we'll drill from the N-pole to the S-pole to minimize problems with the coreolis effect.

Does it not because of the whole /(r^2) in the gravity equation? Kinda hard to divide by 0.

That's not the right way to consider the problem. If you went straight with 1/r^2 your gravitational force would be extremely strong near the center of the earth. Now, while it is true that you are the deepest in the earth's gravitational potential there, the net force you would feel is zero.

EDIT:

saw your point. I keep thinking of the Earth as a point mass.

 

[DrPizza]

Originally posted by: silverpig

Originally posted by: DrPizza
I worked on a similar problem on about 2 dozen napkins during a lunch with half a dozen physics profs... If a hole were drilled through the center of the earth, and an object was dropped into the hole, would it ever reach the center of the earth?

edit: and I better point out that I did NOT say, "ignoring air resistance."
Plus, we'll drill from the N-pole to the S-pole to minimize problems with the coreolis effect.

I'm going to guess no right here because if you consider a 6500km high column of gravitationally supported air, my guess is that near the bottom the pressure would be so great as to liquify the air at least in part.

And, what's the viscosity, density of liquified "air" at that pressure?

 

[Narmer]

wouldn't it just go in the opposite direction since the force is stronger in the second part? Assuming it's in a vacuum, it will never stop.

 

[Atheus]

Wouldn't the ball through the earth be a simple SHM thing, like a pendulum? Clearly not, if it took a dozen napkins and as many physics professors to solve, but why?

 

[WarCon]

That problem only works if time is considered to be purely linear. If time is considered to have a particle or packet aspect/nature then as soon as the equation distance = packet size then the object stops.

In the theory that time has a particle nature (chronons) the theorised minimum length of time possible is called the Planck time and is equivalent to 10 to the negative 43rd seconds.

Linear mathematics creates all kinds of impossible/improbable situations when applied to "real" world applications, hence the creation of theories to explain real world behavior, with real world constants built into the equations, versus theoretical mathematics that don't include said constants or limits.

Just my two cents.

Edit* Sorry for going back to old news

 

[Fritzo]

Originally posted by: TheLonelyPhoenix

Originally posted by: KLin
Boys have a penis, girls have a vagina.

orly?

Yep...here's proof!

 

[LeadMagnet]

Stand 1 meter (yard) from an object then keep halving your distance, you will never get to the object - just real close.

 

[Stunt]

Does it have to do with the square of a number no matter how infinitessimally small will always produce a value greater than zero?

 

[Jeff7]

I believe this is a Theory vs Reality situation, right? Otherwise we'd have some kind of a perpetual motion device.

 

[DrPizza]

Originally posted by: Atheus
Wouldn't the ball through the earth be a simple SHM thing, like a pendulum? Clearly not, if it took a dozen napkins and as many physics professors to solve, but why?

Yes, it is simple harmonic motion - IF you ignore air resistance, which we decided not to ignore.

Plus, as you get closer and closer to the center of the earth, the gravitational force decreases... IIRC, assuming a uniform density spherical earth, the force dropped of linearly.

 

[chuckywang]

Originally posted by: Random Variable
If an object moving along at some constant velocity is subjected to a frictional force that is proportional to the velocity of the object, the object will slow down and come to a stop.

On the other hand, if the same object is subjected to a frictional force that is proportional to the square of the velocity of the object, the object will slow down more rapidly but it will never come to a stop.

Why?

Those situations could never happen physically since the frictional force is always proportional to the normal force.

 

[marvdmartian]

Originally posted by: KLin
Boys have a penis, girls have a vagina.

ROFL!!

More importantly, if a man is standing in the middle of the forest and says something, and his wife is nowhere around......is he still wrong??

 

[bsobel]

Originally posted by: LeadMagnet
Stand 1 meter (yard) from an object then keep halving your distance, you will never get to the object - just real close.

Its a brain teaser, but wrong. If true, no motion would ever actually occur in the universe. In actuality you wind up dealing with plank length. Once you reach that, you are 'there' at the object as you distance doesn't make sense once your dealing with less than plank length units.

 

[Hyperion042]

Originally posted by: bsobel

Originally posted by: LeadMagnet
Stand 1 meter (yard) from an object then keep halving your distance, you will never get to the object - just real close.

Its a brain teaser, but wrong. If true, no motion would ever actually occur in the universe. In actuality you wind up dealing with plank length. Once you reach that, you are 'there' at the object as you distance doesn't make sense once your dealing with less than plank length units.

No, it's not. It's a paradox meant to illustrate that it's possible to take an infinite number of actions in a finite length of time. If you can't do something an infinite number of times, you'd never actually reach anywhere. Ergo, you can take an infinite number of actions in a finite space of time.

 

[bsobel]

No, it's not. It's a paradox meant to illustrate that it's possible to take an infinite number of actions in a finite length of time. If you can't do something an infinite number of times, you'd never actually reach anywhere. Ergo, you can take an infinite number of actions in a finite space of time.

There is no paradox. In the example given you do not take an infinite number of actions. Which you divide the distance down to a plank lenght, you are done. It's a finite numebr of actions in a finite amount of time. Thats why motion works.

The paradox as stated doesn't consider the actual physical limiations of our universe, if you don't like that, go change the laws of nature in your own universe

 

[Born2bwire]

Originally posted by: bsobel

No, it's not. It's a paradox meant to illustrate that it's possible to take an infinite number of actions in a finite length of time. If you can't do something an infinite number of times, you'd never actually reach anywhere. Ergo, you can take an infinite number of actions in a finite space of time.

There is no paradox. In the example given you do not take an infinite number of actions. Which you divide the distance down to a plank lenght, you are done. It's a finite numebr of actions in a finite amount of time. Thats why motion works.

The paradox as stated doesn't consider the actual physical limiations of our universe, if you don't like that, go change the laws of nature in your own universe

In the classical sense though, it still is not a paradox because the limit of the time unit for each movement approaches 1/infinity. Through the use of calculus, mathematically, there is no paradox.