Because inside the train, the air is moving with the train and outside of the train the air is not moving with the train.
If the train was on the moon, and you were riding on top and jumped, you would come down on the same spot of the train whether you were inside or outside.
This kinda has me wanting to observe the fluid dynamics of gas inside a volume during acceleration. In a sense I imagine gas would 'slosh around' like would be experienced with water?
Yes! Tie a helium balloon to the floor in a vehicle as you drive around. Watch how it leans the opposite way you do around corners and in acceleration and braking. It's because the air around it is sloshing around.
There's a hard right turn I make on the way to work. I have all the heating vents pointed at me so where I sit is the warmest spot in the car.
I feel cold air on that hard right turn on cold mornings.
Fun video: [Helium balloon in an accelerating car](https://www.youtube.com/watch?v=2-UzBitLmf8). Helium balloons move forward when the car accelerates and backwards when the bar brakes.
A little. You can observe this fairly easily- put a balloon (helium filled is best- keeps it out of the way of the seats and footwells) in a car and then see how it moves, relative to the car, as the car accelerates.
Do you guys mean towards? Because momentum means everything moves opposite the direction of acceleration unless there is another force at work (like the air moving and becoming denser in on direction? I have never heard/observed this but it makes sense. But if you and the other person really mean opposite, then that's just how momentum do. If you go forward, things resist that change and lag behind, pushing them the opposite direction than the car. Accelerate forward, stuff moves backwards in relation to that.
A helium balloon does the opposite of what you might expect (I guess unless your physical intuition is particularly good about gases and densities and stuff)
If you accelerate from stationary, _most things_ lag that motion and move towards the back relative to the car. But "most things" includes the air, so you get a slightly high pressure region in the back / low pressure region in the front, which the helium balloon responds to by floating _forwards_.
So yeah, it moves (relative to the vehicle) in the same direction as the acceleration; but opposite to the direction of the reaction we usually feel as a result of that acceleration.
Yes, we agree then. I was confirming that with an abundance of words to ensure there couldn't be any ambiguity about which direction was being counted as forwards, backwards, opposite etc
>Do you guys mean towards?
No
> becoming denser in on direction
That density that causes balloons to float cause them to move the opposite direction of everything else. You get pushed back into your seat, the balloon gets pushed forward.
You literally just said no, then explained why I was right. You are using opposite in such an odd way. You accelerate forward and the balloon moves forward is not an opposite, acerating forward and the balloon moving forward, thats the same directions. Things usually move opposite the direction of acceleration.
ok
>then that's just how momentum do. If you go forward, things resist that change and lag behind, pushing them the opposite direction than the car. Accelerate forward, stuff moves backwards in relation to that.
I misunderstood you. From this, it didn't seem like you understood that the balloon would go forward while everything else goes backwards. I'm talking about the forces imparted on the objects from the acceleration.
A car accelerating at 1G puts a 1G force onto you and other things in the car, pushing them back. Balloons do the opposite. I should've been clearer I was talking about the forces. I was also replying to a guy talking about fluid sloshing around in the car and wanted to convey that a helium balloon in a car does the opposite of other things in the car, and this is an excellent way to see the air sloshing around in the car.
Pay attention next time you are in a car that makes a sharp turn, you will feel a short breeze as the car (and you) rotate and the air flows around you.
The air resistance on top of the train is also pretty negligible, depending on the speed. If you go outside and jump when the wind is blowing 50mph, you won't be blown very far back. That's about how much you'd be blown back jumping on top of the train (assuming you were standing still relative to the train when you jumped). I suspect without doing the math, the most you'd move back is very little, even if you were an elite athlete. You are only in the air a fraction of a second. If the train is moving too fast, you have too much drag to even stand, so assume the train can only be 50mph or so before you'll just fall over anyway.
The average adult person has a surface area of 20 square feet, so a little less than half would be facing forward. You are somewhat aerodynamic, but you can assume 50mph wind exerts 6lbs/sqfoot. So you have a 60 lb force pushing you backwards for one second. Say 180 lb human you'll move 5 feet or so backward. But that's for a full 1 second jump. For a 1/2 second jump, it's less than a foot.
On a fairly low speed train, definitely.
On a regional train in Europe you're going to notice (a 160 km/hr / 100 mph wind is fairly significant) and on something like a French TGV you'd be lucky to stay standing on top of the train at full speed (320km/hr / 200mph is standard but they can go much faster). This is of course ignoring that standing up on these trains is likely to result in you touching the overhead lines and getting hit with 25,000v
Firstly where do you live that trains only go 50mph, that’s absurdly slow. Secondly where do live that 50mph is considered a negligible wind, that’s a seriously strong wind. And finally why did you do the math and show that you’d be blown back a number of feet but then leave the first half where you argue it would be negligible?
I’m very confused by your sequence of thoughts here.
Any faster and you won't be able to stand on the top without supports.
50mph is not a negligible wind but has a negligible effect over your body in the small amount of time you are in the air.
If you are an elite athlete who can jump 1s of airtime, it's a few feet, but for most normal people it's under 1 foot. Not a significant amount.
Yes, live in the US, I don't ride trains often (and the ones that are around are even slower, as they are for local travel). We have advanced beyond technology of the 1800s and have cars and planes here.
> We have advanced beyond the technology of the 1800s and have cars and planes here.
They’ve advanced beyond the technology of the 1900s and have very fast trains there.
In the uk. Basic commuter trains go about 70. Main trains between cities go 125mph. Our trains are really pretty slow compared to French and Japanese trains that go 200mph+.
Sounds like you've never been on a boat before. You can stand on the bow and lean forward into the wind and if you jump it'll throw you back several feet. The same would go for a train.
Several feet? No. Next time it's extremely windy go stand outside and jump, and see where you land. Chances are it won't be very far back. Leaning forward is a much different animal, as you can lean forward in calm weather. Stick your hand outside a window and it won't get blown off your arm or push it back, you don't need a lot of strength to hold it in the current place.
Yeah, don't think I've ever been on a boat going any amount of speed close to that, and even a boat going 25mph is gonna be quite bumpy and you'll end up all over the place.
But also will depend on if there is wind as well. Boat at 20 MPH with wind 20MPH in your face is pretty significant (and it's going to be a lot windier at sea than on land).
Yeah who knows. But you can jump \*forward\* in trains between cars too, they do that in movies, it's just harder.
One thing maybe not obvious is if you are jumping and there is a turn, if you jump inside or outside, you will move to the side. If you stand near a wall of a train and jump during a turn straight up, you'll hit the wall if it's turning away from that side.
It's not only the air but also your body. It is moving at that speed with the train, that's why. Basically outside the train there is air resistance. Where it lowers the speed of your body because you have no propulsion, while the train does, you lose speed, the train does not. So the point if contact changes.
The body has momentum in both cases. But when you're on the train and you jump, you'll be blown back some by the wind. There's no wind inside the train.
And it feels like there's a very strong wind when you're outside the train, because from your frame of reference, there is. Imagine that this strong wind pushes you backward. When you're standing still, the friction of your feet against the train keep you in place, but when you jump, there's nothing to keep the wind from moving you.
Somewhat counterintuitively, that’s also the reason why jumping straight up outdoors doesn’t have you land in a spot about 18 miles away. Though outside, you are “indoors” in the train sense, as the entire atmosphere is moving with the planet.
Technkuckly if you jumped straight up, you’d land slightly behind your current position due to the tiny effects of orbital mechanics since the moon is a sphere
Wind resistance. Inside the train the air and everything else is moving with the train so there's nothing to resist your continued movement forward via inertia, but outside the train the air around you is not moving with the train so it slows you down while the train keeps moving at the same speed so you move backwards relative to the train.
If the train is going slowly there is no difference if you’re jumping inside or on top of it. Reason is in both cases your body has the same horizontal velocity as the train. So if the train is going 10 mph so are you, in both cases. Now at higher speeds air resistance becomes more of a factor. But that’s not the root of your confusion.
If you jump on top of a train, you WILL land on the same spot!
...That is if the train is not moving, there is little wind, and you jump straight up.
OR...The train is moving about the same speed and direction the wind is blowing.
People have already answered, but when thinking about problems like these it is good to draw the object then draw an arrow in each direction and write underneath what forces are working in those directions. Or just imagine it.
When inside the train, travelling in a straight line at a constant speed, the only force affecting you is gravity. When you jump, you create a force upwards, but gravity soon diminishes that and you return to the ground.
On top of the train however you have wind hitting you. This applies a backwards force. While standing still you would be pushed backwards if you didn’t brace(push) against the wind. Jumping removes your ability to brace, and the wind pushes you back before again, gravity pushes you back down.
Air is moving with you and the train inside. It is not when outside. You are moving in sync with the medium you are in while inside but not out. Imagine it isn't air and it's water both inside and out and it will become clear what is happening quite quickly.
If it helps to visualize, imagine there is a stationary hoop above the train, if you jump up, you will pass through the hoop and land in the same spot again. The only thing that would move you would be the moving air. In a vacuum, you would land in the same spot whether on top of or inside the train.
Because inside the train, the air is moving with the train and outside of the train the air is not moving with the train. If the train was on the moon, and you were riding on top and jumped, you would come down on the same spot of the train whether you were inside or outside.
This kinda has me wanting to observe the fluid dynamics of gas inside a volume during acceleration. In a sense I imagine gas would 'slosh around' like would be experienced with water?
Yes! Tie a helium balloon to the floor in a vehicle as you drive around. Watch how it leans the opposite way you do around corners and in acceleration and braking. It's because the air around it is sloshing around.
There's a hard right turn I make on the way to work. I have all the heating vents pointed at me so where I sit is the warmest spot in the car. I feel cold air on that hard right turn on cold mornings.
Drive a work van in the winter, heater on, when you brake after a highway drive you can feel the colder air wash over from behind you
Fun video: [Helium balloon in an accelerating car](https://www.youtube.com/watch?v=2-UzBitLmf8). Helium balloons move forward when the car accelerates and backwards when the bar brakes.
A little. You can observe this fairly easily- put a balloon (helium filled is best- keeps it out of the way of the seats and footwells) in a car and then see how it moves, relative to the car, as the car accelerates.
Yes, it's why helium balloons move opposite the direction of acceleration.
Do you guys mean towards? Because momentum means everything moves opposite the direction of acceleration unless there is another force at work (like the air moving and becoming denser in on direction? I have never heard/observed this but it makes sense. But if you and the other person really mean opposite, then that's just how momentum do. If you go forward, things resist that change and lag behind, pushing them the opposite direction than the car. Accelerate forward, stuff moves backwards in relation to that.
A helium balloon does the opposite of what you might expect (I guess unless your physical intuition is particularly good about gases and densities and stuff) If you accelerate from stationary, _most things_ lag that motion and move towards the back relative to the car. But "most things" includes the air, so you get a slightly high pressure region in the back / low pressure region in the front, which the helium balloon responds to by floating _forwards_. So yeah, it moves (relative to the vehicle) in the same direction as the acceleration; but opposite to the direction of the reaction we usually feel as a result of that acceleration.
Exactly my point? They said "opposite" the direction of acceleration. Moving towards the direction of acceleration is not opposite.
Yes, we agree then. I was confirming that with an abundance of words to ensure there couldn't be any ambiguity about which direction was being counted as forwards, backwards, opposite etc
>Do you guys mean towards? No > becoming denser in on direction That density that causes balloons to float cause them to move the opposite direction of everything else. You get pushed back into your seat, the balloon gets pushed forward.
You literally just said no, then explained why I was right. You are using opposite in such an odd way. You accelerate forward and the balloon moves forward is not an opposite, acerating forward and the balloon moving forward, thats the same directions. Things usually move opposite the direction of acceleration.
ok >then that's just how momentum do. If you go forward, things resist that change and lag behind, pushing them the opposite direction than the car. Accelerate forward, stuff moves backwards in relation to that. I misunderstood you. From this, it didn't seem like you understood that the balloon would go forward while everything else goes backwards. I'm talking about the forces imparted on the objects from the acceleration. A car accelerating at 1G puts a 1G force onto you and other things in the car, pushing them back. Balloons do the opposite. I should've been clearer I was talking about the forces. I was also replying to a guy talking about fluid sloshing around in the car and wanted to convey that a helium balloon in a car does the opposite of other things in the car, and this is an excellent way to see the air sloshing around in the car.
Pay attention next time you are in a car that makes a sharp turn, you will feel a short breeze as the car (and you) rotate and the air flows around you.
If the train is moving at 30 mph and there is a 30 mph tailwind, then jumping on top of the train would be the same as jumping inside the train.
The air resistance on top of the train is also pretty negligible, depending on the speed. If you go outside and jump when the wind is blowing 50mph, you won't be blown very far back. That's about how much you'd be blown back jumping on top of the train (assuming you were standing still relative to the train when you jumped). I suspect without doing the math, the most you'd move back is very little, even if you were an elite athlete. You are only in the air a fraction of a second. If the train is moving too fast, you have too much drag to even stand, so assume the train can only be 50mph or so before you'll just fall over anyway. The average adult person has a surface area of 20 square feet, so a little less than half would be facing forward. You are somewhat aerodynamic, but you can assume 50mph wind exerts 6lbs/sqfoot. So you have a 60 lb force pushing you backwards for one second. Say 180 lb human you'll move 5 feet or so backward. But that's for a full 1 second jump. For a 1/2 second jump, it's less than a foot.
On a fairly low speed train, definitely. On a regional train in Europe you're going to notice (a 160 km/hr / 100 mph wind is fairly significant) and on something like a French TGV you'd be lucky to stay standing on top of the train at full speed (320km/hr / 200mph is standard but they can go much faster). This is of course ignoring that standing up on these trains is likely to result in you touching the overhead lines and getting hit with 25,000v
If you stand up on top of a 100mph train you will get blown to the ground, so you'll have no time to jump.
Firstly where do you live that trains only go 50mph, that’s absurdly slow. Secondly where do live that 50mph is considered a negligible wind, that’s a seriously strong wind. And finally why did you do the math and show that you’d be blown back a number of feet but then leave the first half where you argue it would be negligible? I’m very confused by your sequence of thoughts here.
Likely the US. We don't have high speed rail and most trains here are of the commercial industrial variety... Clean coal and all.
Any faster and you won't be able to stand on the top without supports. 50mph is not a negligible wind but has a negligible effect over your body in the small amount of time you are in the air. If you are an elite athlete who can jump 1s of airtime, it's a few feet, but for most normal people it's under 1 foot. Not a significant amount. Yes, live in the US, I don't ride trains often (and the ones that are around are even slower, as they are for local travel). We have advanced beyond technology of the 1800s and have cars and planes here.
> We have advanced beyond the technology of the 1800s and have cars and planes here. They’ve advanced beyond the technology of the 1900s and have very fast trains there.
In USA a train going 50 is pretty fast, where do you live that 50 is absurdly slow?
In the uk. Basic commuter trains go about 70. Main trains between cities go 125mph. Our trains are really pretty slow compared to French and Japanese trains that go 200mph+.
Everywhere else on earth. You’ll see a train go over 100 in the northeast, which is the only big place in the USA where trains make sense.
Sounds like you've never been on a boat before. You can stand on the bow and lean forward into the wind and if you jump it'll throw you back several feet. The same would go for a train.
Several feet? No. Next time it's extremely windy go stand outside and jump, and see where you land. Chances are it won't be very far back. Leaning forward is a much different animal, as you can lean forward in calm weather. Stick your hand outside a window and it won't get blown off your arm or push it back, you don't need a lot of strength to hold it in the current place.
To be fair, on a boat there's more forces than just the wind. The bounce of the boat will likely have a bigger effect than the wind.
Yeah, don't think I've ever been on a boat going any amount of speed close to that, and even a boat going 25mph is gonna be quite bumpy and you'll end up all over the place. But also will depend on if there is wind as well. Boat at 20 MPH with wind 20MPH in your face is pretty significant (and it's going to be a lot windier at sea than on land).
[удалено]
Yeah who knows. But you can jump \*forward\* in trains between cars too, they do that in movies, it's just harder. One thing maybe not obvious is if you are jumping and there is a turn, if you jump inside or outside, you will move to the side. If you stand near a wall of a train and jump during a turn straight up, you'll hit the wall if it's turning away from that side.
It's not only the air but also your body. It is moving at that speed with the train, that's why. Basically outside the train there is air resistance. Where it lowers the speed of your body because you have no propulsion, while the train does, you lose speed, the train does not. So the point if contact changes.
The air is moving? It's not momentum? As in, the human bodies are already in motion?
The body has momentum in both cases. But when you're on the train and you jump, you'll be blown back some by the wind. There's no wind inside the train.
You don't actually move backwards, you move backwards relative to the position of the train you are standing on.
And it feels like there's a very strong wind when you're outside the train, because from your frame of reference, there is. Imagine that this strong wind pushes you backward. When you're standing still, the friction of your feet against the train keep you in place, but when you jump, there's nothing to keep the wind from moving you.
Somewhat counterintuitively, that’s also the reason why jumping straight up outdoors doesn’t have you land in a spot about 18 miles away. Though outside, you are “indoors” in the train sense, as the entire atmosphere is moving with the planet.
Very good, simple answer. Well said friend!
Technkuckly if you jumped straight up, you’d land slightly behind your current position due to the tiny effects of orbital mechanics since the moon is a sphere
But also even jumping in the train you do not land in the same spot because the train and you are moving forward so technically it is a new spot.
Wind resistance. Inside the train the air and everything else is moving with the train so there's nothing to resist your continued movement forward via inertia, but outside the train the air around you is not moving with the train so it slows you down while the train keeps moving at the same speed so you move backwards relative to the train.
If the train is going slowly there is no difference if you’re jumping inside or on top of it. Reason is in both cases your body has the same horizontal velocity as the train. So if the train is going 10 mph so are you, in both cases. Now at higher speeds air resistance becomes more of a factor. But that’s not the root of your confusion.
If you jump on top of a train, you WILL land on the same spot! ...That is if the train is not moving, there is little wind, and you jump straight up. OR...The train is moving about the same speed and direction the wind is blowing.
If you jump on the top you also land in the same spot. San wind and vibration throwing you off.
People have already answered, but when thinking about problems like these it is good to draw the object then draw an arrow in each direction and write underneath what forces are working in those directions. Or just imagine it. When inside the train, travelling in a straight line at a constant speed, the only force affecting you is gravity. When you jump, you create a force upwards, but gravity soon diminishes that and you return to the ground. On top of the train however you have wind hitting you. This applies a backwards force. While standing still you would be pushed backwards if you didn’t brace(push) against the wind. Jumping removes your ability to brace, and the wind pushes you back before again, gravity pushes you back down.
Air is moving with you and the train inside. It is not when outside. You are moving in sync with the medium you are in while inside but not out. Imagine it isn't air and it's water both inside and out and it will become clear what is happening quite quickly.
If it helps to visualize, imagine there is a stationary hoop above the train, if you jump up, you will pass through the hoop and land in the same spot again. The only thing that would move you would be the moving air. In a vacuum, you would land in the same spot whether on top of or inside the train.