if you are in a empty van travelling at 85mph and jumped would you travel backwards as the van is moving ?

Question

My brother cant understand, that you would not move and wont take my word for it so can someone please explain it to him

as he seems to think that if the van is moving and you jump the van will move past your feet and you would not land in the same place

Answer 1

He is right! If you jump up in the air, you will crash on the back of the van at 85 mph. It is going to hurt.

It is just the same with the solar system. It is moving around the galaxy at a speed of 40 km per second. And when I jump up, I usually land in another city. Once I even fell in the middle of the ocean after jumping from a high ledge.

or NOT!

Answer 2

The answers so far have only been partially right, when you are in a van at any speed, you the van and importantly the air inside the van are all travelling at the same speed. So if you jump up you will continue to move in relation to the vehicles speed and therefore land in the same spot.
However if the van had no windscreen and rear windows and you did the same jump you would instantly be thrown backwards and probably out of the van, because the air inside the van will be travelling at what ever speed the van is, but in the opposite direction even on a windless day. That is, at 85 m.p.h. you will be hit by an 85 m.p.h. wind. Try it on the roof of a train or a big dipper and you will definitely die, the experiment only works in a sealed vehicle

Answer 3

You would still be traveling at 85 mph until you hit the ground and died. Your horizontal motion does not stop until something opposes it, like air resistance (not much in this case) or the pavement (a lot).

Later: I read the question wrong and thought you were talking about someone jumping out of the van thru the back. That would require a little push in the opposite direction the van was traveling in order to get your suicidal self out the doors. Otherwise, merely jumping straight up would have no affect on your position inside the van.

Answer 4

Do me a favour, people! You can't explain conservation of momentum to someone who doesn't have a basic grasp on reality.

Use this more graphic example: instead of a van travelling at 85 miles an hour use a jet airliner travelling at 600 mph. If you didn't continue moving forward at the same speed as the airplane when you jumped you would smash out through the back of the plane before you could land back on your feet.

Since no-one has ever suffered such an accident in hundreds of millions of airtrips, clearly it doesn't happen. And it doesn't happen in a van either.

Even better: the Earth's surface is rotating at 1000 mph beneath your feet; when you jump up in the air you don't fly backwards, do you?.

Answer 5

When you are in that van that is doing 85 mph, then you yourself are doing 85 mph also. You better be. SO if you jump, you are doing 85 down that road without a van around you, and that is when it really starts to get rough on your body.

This kind of reminds me of the old falling-elevator question, if you jump up just when it hits bottom, would you be OK? Well, you'd be moving at the speed of the falling elevator, downward, so unless you have enough legpower to jump faster than that already, you will still be falling after you 'jump'.

Anyway, I hope you see, and I would say, don't do it, but if your brother wants to, let him but at a lower, survivable speed. Like 20 or 25, tops.

Answer 6

If you jumped out of the the van, the van and the man would move forward due to momentum. Once you hit the ground, the van is likely to continue to move forwards faster, while the impact will slow the man down.

Try using a skateboard as an example...if you are moving 30 mph on a skateboard and fall off...the skateboard will continue to move forwards, while you will also move forwards but slow down quicker when your feet (or body) hit the ground....

Also if you are on a skateboard and jump up - you both will move to the same point if there is nothing to impede your forward momentum and you will land on the Skateboard.....you are both travelling at the same velocity....

Answer 7

The easiest way to explain this is that if you are in a van travelling at 85mph, then you are also travelling at 85mph. So relative to the van, you are travelling at 0mph, and so are effectively jumping on the spot.

Also point out that the earth is moving (day and night are caused by the rotation) and travels through approx 4,000 miles in one day at the equator, which is about 165mph. If he jumped when standing on the earth travelling at 165mph he would jump on the spot as he is also travelling at 165mph.

Answer 8

Try telling him that as he is in the van when it is travelling then he is also travelling at 85mph relative to the outside world but is stationary relative to the van floor. As he jumped he would loose negligible speed and therefore land in approximately the same place.

You could also use a practical experiment. Next time your in a car, train etc ask him to toss a ball in to the air and watch his amazement as he is able to catch it with ease!

Answer 9

When you are sitting in the van, you are the van are both moving at the same speed. Your relative speed to the van is zero since you are not moving with respect to the van.
When you jump into the air, you are applying a force to push you up and your velocity changed in that direction. But perpendicular vectors are independent and one's speed in one direction (upward) will not affect one's speed in another direction (side to side). You are jumping perpendicular to the van's velocity. Since your horizontal velocity was originally the same as the van's and you are not doing anything to change it by jumping (that is only changing your vertical velocity), all the while you are in the air, you will be moving along with the van along the road at the same rate. When you land, your relative speed to the van is still zero (as has been the entire time you were in the air) so you did not move relative to your original position within the van.

When you push upward it does not change your horizontal speed, it only changes your vertical speed. You will not move relative to the van (in the horizontal direction) since both of your speeds are the same (in that direction).

Now if the van was to accelerate while you were in the air (for example, if the driver pushed down on the accelerator (or brake), then the speed of the van would change but since you are no longer 'connected' (so to speak) to the van, you will not accelerate as well. In this case, your relative speed to the van becomes non-zero and you will land in a different spot than you jumped from.
If you did not jump, then when the van accelerated, the force of friction between you and the seat/floor would act to accelerate you as well and you would move with the van. But if you were in the air, the seat/floor would not exert that force on you so your horizontal velocity would not change.


(Is the van truly empty if you are in it?)

Answer 10

Okay explain it this way to him or get a van and do this.

The van is a a standstill and you are in the back. The van accelerates to 85mph...what speed are you travelling at. You then jump and land what speed are you travelling at.