question on a fly's motion

Lets imagine a fly with some velocity finding its way inside a train. When the train is in motion, the fly neither sitting on a wall nor having a seat , does it increase the fly's velocity to the train;s velocity, in other words will the fly travel along like men do ?

Regards
drdolittle

that's where "frame of references" play their role.....the fly is in the frame of reference of the train.....well...let me ask u ...if u toss a coin vrtically upward while sitting in a moving car at uniform velocity of 100 km/sec....the coin comes back in ur hand or it sticks to the back seat of the car...certainly it comes back in yr hand...y?....because the coin is also present in the same frame of reference.....but if the velocity is not uniform the coin will not come back in yr hand...similerly if the velocity of the train is not constant the fly will also experience a force on it.....lets say the train suddenly accelrated from 0km/sec to 200km/sec in just 0.25secs....certainly the fly will stick to the back of the train like u will to the back of the seat....but if the acceleration is very slow then the fly would experience almost the same force like u experience while the train is accelerating....i hope u will understand from this......sidra_maheen84(at)yahoo.com

if the fly were to accidently enter the window...maybe the window swallowing it up and the fly was initially at a lower speed than that of the train... I believe it is gonna get pushed back to the end...but it would gradually atttain the speed of the train.

Thats why i mentioned the fly not in contact with the train to make it explicit that they are not in the same frame of reference. When we travel we are in contact with the train and thus we move with the velocity of the train(considering all those initial backward movement). That is, when we drop a ball inside the train it looks to fall vertically down to us but for a person outside the train,with a different frame of reference, it appears to take a parabolic path. This is analogous to galileo's discussion.
so what will happen to fly which is not in contact with the train ? My feeling is it will be hit by the back end of the wall and splatters(in accord with the conservation of momentum).

Regards
drdolittle

The fly velocity is with respect to the local air around it. That is why fly swatters have holes so it does not push the air around the fly.

i have told that when the train accelerates the fly certaily feels a back ward force on it due to law of inertia...exactly like us.....but after some time when thw velocity becomes uniform the fly adjusts itself according to the frame of the train...again like us...

TO sidra

whatever you said is absolutely right as long as THE FLY AND TRAIN ARE IN CONTACT. If there is no contact the fly is not in train's frame of reference yet. It still maintains it's velocity.

Regards
drdolittle

I strongly agree with DRDolittle.The fly is in the frame of ref. of the train only if it is in contact with the train.

when u toss the coin in a moving car.. the coin is initially in contact wth ur hand... so it carry the car velocity... so it come back to ur hand after some time..

but if the fly is in the moving car...if the fly has to move forward in the car... it has to fly wth extra speed compare to when the car is static...

my opinion...

sp

well...anyways...the question was good and i really enjoyed it.....keep asking this kind of questions on this forum....thx to all other guys too.....well it is really complicated to discuss the frames....we can hv some idea by looking around us....n we can see this kind of cases everywhere arount us..