Here is a Q that I can't wrap my brain around.

1. If you are on top of a train, running from back to front, does that mean that you're going faster than the train?

2. If you were to jump off the train after the initial run, will your distance be farther than if you jumped without running?

3. If you dropped a rock from the train to hit an oncoming signboard. will the impact be the same as if you were to throw that same rock at that sign board (while on that train)?

Explanation and links appreciated.

This post has been edited by TheDoer: Sep 16 2010, 10:12 AM

Sorry, edit, Q3. Throwing the rock, while on the train, which means that you're already travelling at 60km/h in addition there's the force from you throwing the rock.

Thanks for the reply. Keep them coming.

Q4. Can you think of an easy & safe experiment we can do to prove this?

Ah... thanks.

haha... no it's not my homework. I'm seriously pondering on this. I'm hesistant to throw rocks from a moving vehicle I don't think that's safe.

I guess the military would have done such experiments. But Ramjet is just a jet type, I couldn't find any specific info about stacking velocity.


Ok, I've gone through the wiki, doppler effect refers to the sound waves compressing as we head in their direction, causing them to appear to have a higher frequency.

But I don't think I can test this to prove either.

The word Stacking Velocity was just coined for lack of knowledge what the physics world calls this effect. Would be good if someone could drop me more keywords.

You know I began asking the TS questions, because thinking, that if I travelled on a speeding train, and jump to the front of it, I'd very soon get rammed by the train, therefore, what happen to the initial inertia while on the train? Does that mean that my moving on the train was just a temporary borrowing of the trains inertia, whereby my running on it doesn't stack?

The strange thing is, if for example, there was another train travelling at the same speed infront of that train, and I jumped, I would land smoothly on the other train without loosing much, why is that?

The answer is that, the only reason we decelerate so fast after leaving the train is the air friction and other resistance. The faster you travel, the stronger will the air friction be, which is why, you will fly backwards if you try to jump of the train.

It doesn't have to be a vacuum, in the cabin of the train itself, the air around you are travelling at the same speed as yourself, so whatever you throw in it, will have the same reaction, as if you did the same experiment on solid ground. The moment your cannon ball leaves the cabin, it will be blasted with air, such as it would at the speed of the train + the speed of the cannon ball, causing it to greatly decelerate.

However you have choosen a cannon ball, which has an aerodynamic shape, and the weight gives it more momentum, therefore the wind blast will have less effect on it. Such as what happens when you drop a marble and a feather, the marble will drop faster.

This post has been edited by TheDoer: Sep 17 2010, 10:18 AM