Haiz.
this is soooo easy -.-
basically, let's say you jump on an mrt train (train easier since
no nid to discuss humps etc)
situation 1: the train at the station, doors open, you walk in, the
train not moving, you jump, you land back same spot.
everyone knows that.
-----
situation 2: the train doors closed, it is travelling at a constant
speed of 80km/h. you jump, you land back same spot.
you are asking - why?
i'll get back to this later.
-----
situation 3: the train door beep beep then close, you are holding
on to the pole, the train start moving, you hear the engine getting
louder - what do you feel? you feel as though you are falling
backwards towards the back of the train for the initial
moment.
if you were to jump at this point, technically you won't land back
at the same spot. you would probably land about one centimetre
further back from the spot you jumped up. how far back you land
depends on how fast the train is accelerating and how much time you
spend "in the air".
but you probably would't want to use all your effort to jump since
1) you will hit your head 2) you will fall backwards when you land
unless you quickly hold on to something since the train is
ACCELERATING.
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situation 4: you are standing still holding the pole, the train is
moving at a constant speed, then it gets closer to the station and
it begins to slow down. you can feel that the train is slowing down
and you tend to fall forward towards the front of the train.
if you were to jump at this point, you would also not land back at
the same spot. instead, you would land somewhere further FRONT of
the original spot. how far front you land depends on how fast the
train is slowing down and how much time you spend "in the
air".
-----
in situation 3 and 4, if the train had no roof and you could jump
as high as you want, you will see this happen for sure and you will
definitely fall down -.-
in situation 2 - the one you are asking about - it is actually
exactly the same as situation one.
why you land back at same spot? because the train is at a CONSTANT
SPEED where acceleration is ZERO.
(situation one is also constant speed, because it's speed is ZERO
as long as it's not moving)
whereas in sit 3 and 4, the speed is changing and thus there is
acceleration/retardation. in this case, your body has inertia. say
the train was travelling at a constant speed of 80km/h. your body
is also travelling at the same speed. you listen to your creative
zen mp3 player and dream of a chiobu you saw just now when suddenly
the train apple EMERGENCY BRAKE because in front got one pontianak
that look like the chiobu you were dreaming of. your body wants to
STAY at 80km/h but the train wants to STOP and so you FALL FORWARD
unless you hold on to the pole for dear life while thinking about
how to take photo and send to stomp about this bad service
later.
so yea. if the bus e brake and you jump at the same time, you will
not land at the same spot. you will fly forward through the
windscreen causing a PIANG sound and drop out to the road in front
of the bus and a few minutes later some kaypo will take hp camera
and take photo of you and the bus license plate number and send
both to stomp *while* making sure to buy 4D later.
Also, the police will never know that you were trying to learn
physics. I suggest you write a note and laminate it and put it in
your wallet before you attempt this or else your death will be
ruled as a misadventure.
=)
