The Fly, the Humming Bird, & the Coach.....

[Kizzi]

Let's say a coach is travelling along a motorway at 100Km/H, and in the coach is a humming bird and a fly.

 

The fly is flying about with out landing. Does this mean the fly is flying about at speeds of approximately 100km/H?

 

The owner of the humming bird releases the bird on the 100 Km/H coach, and the humming bird tries float as they do in the air. Will the humming bird hit the back window of the coach at 100Km/H?

 

Or is it all relative to the speed of the coach? The fly is really flying at it's usual speed relative to the speed of the coach? And the Humming bird will be stationary in the coach, so it won't hit the back window?

 

KiZzI :hihi:

[alxian]

the air they are flying in is moving along with the coach at 100Kmh

 

since the whole system is travelling you can't really say anything besides the coach is moving unless its motion opposes the coach.

 

 

if you open a window and allow the air to travel at a relative 100khm opposite of the coach (most lkely somewhere between 0-100kmh and faster in some areas) your fly may indeed become a work of natural art on the back wall if he doesn't clear it on the way out a window with the air that would rather remain motionless without an outside wind further complicating up your example.

 

that is to say the fly retains its 100kmh of momentum imparted to it by the coach (either by the air had he never settled or any surface within the coach) simply because nothing opposes it, its inertia is not affected by the otherwise motionless air in the coach.

[Qfwfq]

Galileo's famous dialogue, published around 1632, contains a lengthy discussion of these things ending with a passage that is considered the first published statement of the principle of relativity. Newton refers to it in Principia as "the experiment of the ship". The discussion in the dialogue is on the third day, aimed at showing that Earth can be moving despite we hardly notice it.

 

Find out your latitude and work out how fast the ground under your feet is travelling due to Earth's rotation, you might be mildly suprised. Despite your northerly location Kizzi, it'll be a spot more than 100 mph!