When you jump on top of a moving train năm 2024

act as if there's a force forwards on them. For this reason, when you slam on the brakes in your car, you are thrown forward and bang your head on the dashboard.

However, it's important to remember that everything in this frame gets thrown forward also. For example, flies and air molecules and helium balloons are thrown forward also. So what happens to a helium balloon in a decelerating train?

While you are thrown forwards, a helium balloon is actually thrown backwards when you slam on the brakes! This happens (even though there is a forward force on the balloon from the decelerating frame!) because the air around the balloon is heavier than the balloon itself, so when the air is thrown forward, it pushes the balloon out of the way (i.e. backwards). You can find cool videos of this on Youtube.

Aside: here's a slick way to prove what I just argued. Einstein's theory of equivalence says that a reference frame with acceleration can be modeled exactly by an inertial frame with a force of gravity in the opposite direction. We know that helium balloons move in the opposite direction as gravity (since they are lighter than air). So, if we slam on the brakes (accelerate backwards), we feel an "effective" gravitational pull towards the front, and so the helium balloon moves against this towards the back. Awesome!

So, what happens to a fly? Well, a fly is a lot heavier than an air molecule, so it flies forward just like a human.

I know it's a joke but if we assume we don't have air resistance what exactly will happen if someone jump in the upward direction from a roof of on a moving car? Unless a force is applied to him will he land in the same spot he jumped from on the car? And why (in technical terms)?

Qmechanic♦

199k44 gold badges529 silver badges2223 bronze badges

asked Feb 13, 2022 at 12:48

$\endgroup$

3

$\begingroup$

Newton's first law of motion answers your question, the principle of inertia. If the car is at constant velocity everything inside the car will follow with the same velocity. If no other forces are applied to the person, once it jumps, it will still have the car's velocity due to inertia and will land at the exact same spot over the car. It doesn't matter what kind of situation it is, if you can assure there is no net forces acting, the result of the jump will be the same.

If the car is accelerating, however, it changes. If the car is gaining speed, then once the person jumps, it will lag behind the car because the car is still gaining speed while the person isn't. If the car is losing speed, once the person jumps it will get a lead over the car.

answered Feb 13, 2022 at 14:00

Klaus3Klaus3

4521 silver badge6 bronze badges

$\endgroup$

1

$\begingroup$

If we assume that the car is not accelerating (and is therefore an inertial frame of reference) then the person would fall into the pool.

Why? Because the same happens when they're on the ground. There is no difference between the laws of physics in two inertial frames (moving with constant velocities relative to each other). The earth itself is (approximately) an inertial frame of reference.

In a non-inertial frame, however, the situation would be different. Depending on whether the van is accelerating or decelerating, the person would fall backwards or forwards respectively.

answered Feb 13, 2022 at 13:11

$\endgroup$

2

$\begingroup$

I know your question asks what happens without air resistance, but the picture is more realistic than that. As soon as the man jumps, air resistance will apply a braking force, and he will move backwards relative to the pool.

What is it called when you jump on a train?

Train surfing (also known as train hopping or train hitching) is the act of riding on the outside of a moving train, tram or other forms of rail transport.

What happens if you jump in a moving train?

When moving with the train, the speed of the train is your speed. You are in the same frame of inertia. When you jump in the train, you do not encounter air resistance, and you usually encounter little to no force and there is no change in your speed. That's why you fall in the same place when you jump.

Why do you move if you jump on top of a train?

It all will do the train for you or instead of you! So relative to such a system, your position does not change because it shares its own speed with you. Thus during the straight-up jump, both the train and you are going to travel about the same distance.

What happens when you jump on a moving vehicle?

If the car is accelerating, however, it changes. If the car is gaining speed, then once the person jumps, it will lag behind the car because the car is still gaining speed while the person isn't. If the car is losing speed, once the person jumps it will get a lead over the car.