I haven't tried it but I disagree. But why answer your own question in the first post?

F=MxA. Since it's a constant velocity train, the train wasn't acting on the ball before either. Yes, it will fall straight relative to the cabin. Reminder, velocity is a vector, so the "constant velocity" train also cannot be going around a corner, or up / down a hill - it was, and is, going in a straight line. So, if the cabin were tall enough, the curvature of the earth will void my assumption above, that the "constant velocity" was accurately describing the train's motion.

A 100 foot tall train isn't capable of velocity, the sway would topple it over and crush the ball (and the mathematicians studying it).

Number one (to lawman) there was an old post about this; I couldnt reply to it so i put my 'reply' here in a new thread.


2: to RhinoFish: The train acted on the ball at some point or the ball wouldn't be moving with the train now would it?

Remove the ball from the train (by dropping it, assuming it is touching no walls)and it will start to lose the velocity imparted by the train in favour of gravity.


3: to Seven Cubed. This is called a thought experiment using hypothetical situations to envision rules of physics. they are necessary, and im sure if you took any schooling your teachers (and einstein also) used such hypotheticals.

[edited by: lawman at 2:55 pm (utc) on Sep 20, 2013]

There are thousands of ways you could make a hundred foot tall train... but thats not the point here...

[edited by: lawman at 11:11 am (utc) on Sep 20, 2013]

You from London?

Inquiring minds want to know: What is the point?

Other than the three errors in a single sentence, which is a bit ironic in the circumstances.

Assuming:

1) the train is travelling at constant velocity
2) the track is flat and straight
3) the train is travelling slowly enough that the curvature of the earth is negligible over the distance it covers
4) The train is enclosed, so that the air is the train is still and travelling at the same speed as the train.

then:

The ball will keep its horizontal velocity (Newton's first law of motion) as long as no force acts on it.

Gravity acts on the ball vertically downwards, so it will accelerate the ball downwards, but not affect the horizontal component of the velocity.

Both ball and train are travelling in a straight line at constant velocity, so the horizontal component of their velocity remains the same.

So the ball falls straight downwards.

@treant, the key to understanding this, is that gravity pulls straight downwards, so it does not affect the velocity at which the ball is travelling horizontally. The train acted on the ball to accelerate it, but once accelerated it keeps its velocity. If the train was open, it would be slowed by air resistance, but with the air travelling at the same speed as the train this does not happen.

the train is travelling slowly enough that the curvature of the earth is negligible over the distance it covers

:: detour for business with calculator ::

100ft (height of cabin in our hypothetical train, which I hope won't have to pass through any tunnels) = curvature of earth over a distance of around 12mi (20k).

Does that sound about right, or did I misplace a decimal point?

Okay. Gravity pulls the ball straight down.. but the velocity is forward. so the gravity will start to cancel the forward velocity.

The mere fact that the train was required to bring the ball up to horizontal velocity means that when it is no longer in contact with the ball it will decelerate.

The relationships you are talking about are only valid out in space where there is no earth or sun's gravity.


BTW. I'm a Canuck. From Winnipeg, Manitoba. Not London, mate ;)

Every single molecule of the earth has gravity. The ball isn't simply being pulled to just the center of the earth. For the ball to travel horizontally across the earth it requires constant energy to continue traveling laterally so close to the surface.

For something to remain in orbit at a distance of only a few feet from the surface of the earth (assuming no air friction) it would have to be going like half of the speed of light or something.



And the point of this is I wanted so much to jump into the fray and combat some of the terrible misconceptions that people had in the other thread but it was closed... I can see why they think what they think, but I can also see that it is wrong and I am trying to correct these people.. Who seem like they are much more educated than me... Ironically.

This is fun stuff to talk about, but I'm not sure why you feel the need to bring up a 4 year old thread to combat terrible misconceptions (real or perceived).

I got nothing better to do. Evidently nor do you! hahahaha :)

btw they are real misconceptions; i can back that up... that's why i am here!

@treant, the key to understanding this, is that gravity pulls straight downwards, so it does not affect the velocity at which the ball is traveling horizontally.

OF COURSE gravity affects the horizontal velocity... THINK ABOUT IT.

THE TRAIN NEEDS AN ENGINE TO REMAIN AT VELOCITY FOR THE SAME REASON THE BALL WILL DECELERATE WHEN NO LONGER IN CONTACT WITH THE TRAIN..


gravity pulling DOWN on something will slow its horizontal movement.. just think about it man.. sit there and imagine if pulling down on something would slow down its horizontal speed.

the principles you speak of are only valid in SPACE. not ON EARTH. because the earth acts as a CONSTANT accelerator.. it slows ALL movement to be in sync with the center of it.

To move in ANY direction for ANY length of time away from the center of the earth requires CONSTANT energy because gravity is a CONSTANT application of force.

Therefore.. when the link between train and ball is broken it stops being pulled by the trains engine, and slows its horizontal speed. This will only be noticed at a distance of several meters.

Okay. Gravity pulls the ball straight down.. but the velocity is forward. so the gravity will start to cancel the forward velocity.

The mere fact that the train was required to bring the ball up to horizontal velocity means that when it is no longer in contact with the ball it will decelerate.

The relationships you are talking about are only valid out in space where there is no earth or sun's gravity.

How the ball - or the train - got to their velocity is not material to the issue. Barring other outside forces, the horizontal velocity is constant and is not effected by the force of gravity. Although the vertical velocity will increase from 0 to whatever, the horizontal velocity is constant. This is pretty basic physics.

Speed and velocity are not the same things.

THE TRAIN NEEDS AN ENGINE TO REMAIN AT VELOCITY FOR THE SAME REASON THE BALL WILL DECELERATE WHEN NO LONGER IN CONTACT WITH THE TRAIN..

Nope, reason is not the same. Train needs an engine to maintain speed primarily because of frictional forces. Frictional forces on the ball are negligible.

I know speed and velocity are different. velocity is a vector. it has a force component and a direction component.

the movement of the ball is ENTIRELY affected by gravity in ALL DIRECTIONS. gravity pulls it down. which means for the ball to move laterally in relation to gravity it needs a force to propel it.

the ball must literally FIGHT gravity to move in any direction counter to the force of gravity.

Barring other outside forces, the horizontal velocity is constant and is not effected by the force of gravity.

Says who? That's not true.. That may be true out in space. Remember. please think of this ONE SENTENCE:

For the ball to move in ANY direction other than down, it is FIGHTING GRAVITY TO DO SO

AHH #*$! i think you guys are right....

The moon "has to fight gravity" to stay where it is... and its horizontal speed (for these purposes) is not changing... so.. therefore the only difference could be friction. so a baseball, if there were no air, would fly horizontally at the same speed while gravity ads an additional velocity downward until it hit the ground.


I think..

the ball must literally FIGHT gravity to move in any direction counter to the force of gravity.

It only has to fight it if it's moving up and wants to keep moving up. Otherwise it's not fighting gravity; it gives in to the force (acceleration) of gravity. However, gravity does not affect horizontal velocity.

Where did you get your training and/or what treatises/journals are you relying on. A link to some non-commercial site that explains your position would be helpful.

i got nothin man. just what i thought was common sense and im interested in such things... hit me up with some science and learn me good :)

A good search term ought to bring up more than you care to read.

A great introduction to quantum physics the real question is though from what observation point are you at........ Inside the train or standing at the platform watching the ball drop as the train speeds by

Of course this questions perspective and many argue that perspective can produce several answers

It's all relative, assuming the train is moving at a constant speed the ball will drop vertically as before dropping it is moving at the same speed, a 100 foot cabin is not high enough for any deviation to be noticed by any observer.
_{Possibly this is qustion is being taken too seriously. Nice double decker trains in the Netherlands, always a treat, not 100 feet though.
He said to her 'I love you' she died what was the situation}

@treant, yes, you got it. It follows the same laws as the moon's orbit.

As for air-resistance, if the train is closed the air will be moving at the same velocity horizontally as the train and the ball, so it would have no effect except to slow the acceleration caused by gravity - relative to the air the ball will fall vertically.