seen it on twitter and I can’t get my head around it
EDIT: thanks guys I get it now 😅
In: Physics
I would say speed and distance.
Typically a moving train that you’re jumping into, is still going very slowly (otherwise I wish you good luck…..). And also the distance you’re jumping is very small. You’re jumping only a few feet horizontally, after you matched your speed to the slowly moving train. So yeah, as long as you match the speed you will land kinda where you were aiming. Kinda, because typically the train will be accelerating (slowly) and you can’t accelerate mid air. 😋
Whereas people jumping on to trains in movies (don’t try it at home) typically jump onto a train moving at moderate to fast speed. So they are unable to match the forward momentum of the train. AND they are jumping maybe 10 to 20 feet vertically from a bridge. More like “aimed falling” than jumping. 😅 And during falling, simple gravity acceleration rules will apply. During that second or two that falling 10 to 20 feet will take, the train will be moving under you.
From km/h to m/s, you need to divide by 3.6.
So let’s say the train is moving at a modest speed of 36km/h to keep it easy. That’s 10 meters that the train will have moved forward if let’s say you are falling for 1 second. Sure, you too will have moved forward some if you took a running start before jumping off the bridge. But surely not 10 meters.
Ideally, both scenarios will result in you landing on the same spot. This is due the fact that when you jump, you are still moving at the same speed as the train. The difference when you’re on top of the train is that air resistance will drag you down and you’ll land short.
Air resistance
The air inside the train is being dragged along with the train because the train carriages are enclosed boxes.
If you jump, the air moves with the same speed as you, and doesn’t drag you back.
The air outside the train doesn’t get dragged along with the train, and is usually stationary relative to the ground.
As you jump, you’re moving at the speed of the train through the stationary air, and the air pushes against you a little, slowing you down and meaning you land a little closer to the back of the train
If you jump outside on a still day you land on the same spot.
If its a day with 160kph winds you’ll land a bit downwind
When you’re inside the train, basically everything is moving at the same speed (all things being equal).
When you’re outside, there are outside factors that will change where you land – air resistance, wind from any direction, etc.
Momentum.
Inside, you are moving the same speed as the train and so is the air inside. Outside, you are moving the same speed as the train, but when you separate from the train by jumping, you are transferring momentum to the air particles you are bumping into.
If you are moving with constant speed, you technically should land on the same spot but if you are on the roof, there´s a lot of air resistance and that will slow you down so it would be like you landed behind from the spot you jumped
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Everything inside the train is moving at the speed of the train. This is not the case outside of the train. Outside the train, the train is moving faster then the air surrounding the train. So, essentially you are pushed back by the air surrounding the train.
TLDR – the air surrounding the train pushes you back if you are outside the train.
Air resistance.
In both cases, before you jump you are travelling at the same speed as the train.
If you jump inside the train then all the air on the train is also travelling at the same speed as the train so it doesn’t slow you down.
If you jump on the roof of the train, the air is not moving at the same speed as the train so it effectively pushes you in the direction opposite to the train’s travel.
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