Hi !
when getting off a running bus or a train we put the left foot first on the ground if we are getting down from the left side, why?
If we put the right foot first on the ground we fall down on the pavement.
What's the physics behind this?
thanks !

 

I assume the right food is next to the train. I suspect it has more to do with your feet getting tangled together.

 

I would put it down to a timing issue rather then entanglement.

In the time between putting two foot down the train has moved some, meaning your feet are already spaced apart as if you have taken a step. Thus you need to be instantly ready to take another step from the fist foot to be moved.

To get off on the left side, left foot first is like so:

1) slide left foot to left, apply weight.
2) slide right foot to left, apply weight. (note your left foot is now behind you)
3) bring left-foot forward (take the first step completely off train)
4) now walk (or run) right-foot-left-foot till normal walking pace, or a complete stop is possible.

That is a simple sequence of moves where the movement of the train works with you to spread your feet apart for the next step.

To get off on the left side, right foot first is like so:

1) slide right foot to left (but behind left foot), apply weight.
2) slide left foot to left
3) slide left forward, apply weight.
4) bring left-foot forward (take the first step completely off train)
5) now walk (or run) right-foot-left-foot till normal walking pace, or a complete stop is possible.

Ugh, you probably fell down at step 3. To use the wrong foot it may be best to just hop off completely and land on that foot.

 

This reminds me of the time when a friend used to give me a lift to middle-school on the back of his pushbike.

For some idiomatic reason, I enjoyed jumping off the back when he was going really fast.

I don't think I had a choice which foot landed first, I just had to make sure I ran really fast to avoid falling over on the tarmac!

 

I imagine it would be because you are usually facing forward when you are about to step off (you walk towards the front of the bus). If you're facing even slightly forward when you're about to step out, you would put your left foot out first, or else you would have to cross your right foot in front of your left. This would cause you to become unbalanced, and possibly fall.

This is the only reason I can think of. I imagine it would be different if you were stepping directly off (some buses have steps that go straight out from the side). It could also be different for different people. One leg is often slightly longer than the other. Who knows? It might even boil down to the earth's rotation

I'm joking, of course. Honestly, I have absolutely no clue

 

First of all, I think a person could train himself to get off either way, assuming the bus is not going too fast, but I can definitely see a novice having better luck putting the left foot down first. I am answering as an american who drives on the right side of the road, and I expect the bus door to let me out on the right side.

From a physics point of view, my guess is that it is more of an issue of torque than anything else. The friction between foot and pavement induce both a force and a torque on the body. Right foot down will spin you from facing right to facing backward, while left foot down will spin you from facing right to facing forward.

 

I'd probably fall on my face regardless of side or foot. I still have trouble with the moving walkways at airports.

 

I imagine it would be because you are usually facing forward when you are about to step off (you walk towards the front of the bus). If you're facing even slightly forward when you're about to step out, you would put your left foot out first, or else you would have to cross your right foot in front of your left. This would cause you to become unbalanced, and possibly fall.
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Agreed! It's an issue of the possible degrees of movement of each leg. If you have the right foot on the bus and the left foot goes down, it has basically nothing to stop it going back so there is no "trip" and maximum time to move the remaining foot.

But if you jump totally off so you are clear of the bus and both legs are pointing forward it doesn't matter which leg you use first.