Relativity Problem: Small fly inside moving vehicle -am I stupid?

[transistor495]

Hi all.

This is a problem I've been watching for a couple of months. This can be a very stupid question though, I don't get it actually.

Suppose I'm travelling in a vehicle(car) at 100Kmh(or more just imagine for now), and there is a little fly which can barely fly 30Kmh in open air -is bugging me inside the vehicle compartment.

Scene 1: Fly is just balancing on air without moving in any direction. Then relative to the vehicle, the speed of fly is 0. But relative to a person watching from outside(road), fly is flying at vehicle speed ie, 100Kmh.

Scene 2: Fly is moving in zig-zag direction. That include forward/backward also comparing to the moving vehicle direction. During backward, the fly is still going 100Kmh relative to an outside viewer.

Question: How is this possible as the fly is not touching/sitting in the vehicle and is on air(air inside vehicle).
The only solution I can think that the air inside the vehicle is closed with respect to the vehicle and it is moving with vehicle.

If that is the case then what about an open body vehicle which doesn't have a closed compartment? Surely it doesn't have an air compartment associated with that. But I'm sure that the same fly can do the same trick in this case too.

What is your thought on this? Just curious to know. Don't call me an idiot please

 

[ronsimpson]

In the inclosed vehicle the fly is going 100. The fly thinks it is going 0 because it is not moving compared to the air it knows about and all it can see.
Take away the top and windshield and there are huge wind forces that will eject the confused fly.

As I sit infront of my computer, I think I am not moving. The earth is racing around the sun. The sun is shooting through space.

 

[canadaelk]

What happens if the fly is wearing a seatbelt while in the moving convertible? E

 

[killivolt]

Bullet fired in a plane.

Reminds me of the Bullet Fired in the back of a plane at aimed at a man in the front of the plane, The bullet is fired at 1200 ft/s and the plane is traveling at 1200 ft/s.

Will the bullet just fall to the floor or strike the man in the front of the plane ?

 

[ericgibbs]

Reminds me of the Bullet Fired in the back of a plane at aimed at a man in the front of the plane, The bullet is fired at 1200 ft/s and the plane is traveling at 1200 ft/s.

Will the bullet just fall to the floor or strike the man in the front of the plane ?

hi kv,
The gun that fires the bullet is moving at 1200ft/s and the bullet leaves the barrel at 1200ft/s, so if the guys aim is good, then there is one less for dinner....

 

[3v0]

Both of these problems deal with frame of reference. With KV's example the plane is the frame of reference.

 

[atferrari]

Provided that...

hi kv,
The gun that fires the bullet is moving at 1200ft/s and the bullet leaves the barrel at 1200ft/s, so if the guys aim is good, then there is one less for dinner....

As long as it is not the pilot or myself, please, go ahead and shoot...

 

[birdman0_o]

One conceptual problem I personally like is...

Say we drop a bowling ball from an airplane that is traveling at 1000km/h high up in the sky. Ignoring wind resistance, how will the ball fall according to people on the plane? According to people on the ground?

 

[cr0sh]

One conceptual problem I personally like is...

Say we drop a bowling ball from an airplane that is traveling at 1000km/h high up in the sky. Ignoring wind resistance, how will the ball fall according to people on the plane? According to people on the ground?

Assuming no resistance, the people on the plane would just see the ball receding away from them toward the ground. From their reference point, the ball is dropping straight down. To the people on the ground, they would see the ball moving at an angle, with a horizontal velocity equal to that of the plane (so the ball would always be directly under the plane, assuming the plane doesn't change direction or velocity), and a vertical velocity imparted by gravity.

 

[Pommie]

At constant speed the fly can hover. If it really annoys you then slam on the brakes and it will be pinned to the windshield. I can vouch for the fly getting ejected from an open top car.

An other interesting thing to think about is helium balloons in cars, slam the brakes on and they are pinned to the rear window. Go around a corner and they move toward the center.

Mike.

 

[rogs]

Makes my brain hurt, these vector problems!

The one I really don't get is the speed of light one. Nothing can travel faster than the speed of light, we are told.
So if a photon of light is travelling, at the speed of light (obviously) in one direction, and a second photon travels at the speed of light in the opposite direction, then surely the first photon, viewed from the second, is receding, relatively, at twice the speed of light. But as nothing can travel faster than the speed of light?.......As I say, makes my brain hurt!

 

[cr0sh]

An other interesting thing to think about is helium balloons in cars, slam the brakes on and they are pinned to the rear window. Go around a corner and they move toward the center.

When you think about it, I would bet that the reason this happens is because the air inside the vehicle's cabin, being more dense (thus more mass) than the helium in the balloon (plus the mass of the balloon material itself - latex or mylar), "sloshes" forward, or against the sides; the balloon being less dense, moves aside. That's my reasoned guess...

 

[Dr_Doggy]

its just relative is all,, they arn't really going faster, just in "perspective" (you will never be able see a photon that is NOT traveling towards you); unless it bounces back or falls in to a gravitational curve and does a u turn.

look at the fly question again instead thou use a goldfish in water, the fish is simply thrusting water behind it to create its 30 km momentum,, well that car is going 100km in the same direction, using the road traction, so that sums to the 130, IN PERSPECTIVE TO THE GROUND,, but the ground is also spinning/traveling at 10000km/h in the same direction so now the fish is actually going 10130 Km,, relative to its original position IN 3D SPACE

SO ACTUALLY THE FISH NEVER MOVES in accordance with its own perspective!

 

[KeepItSimpleStupid]

I hated doing these types of problems.

 

[transistor495]

Reminds me of the Bullet Fired in the back of a plane at aimed at a man in the front of the plane, The bullet is fired at 1200 ft/s and the plane is traveling at 1200 ft/s.

Will the bullet just fall to the floor or strike the man in the front of the plane ?

hi kv,
The gun that fires the bullet is moving at 1200ft/s and the bullet leaves the barrel at 1200ft/s, so if the guys aim is good, then there is one less for dinner....

Here's another case.

Suppose I'm standing on the top of a mountain and a plane just passes nearby at 1200ft/s. I see my enemy in the plane and shoots at 1200ft/s going bullet.

The interesting thing is that the enemy can see a bullet following him at constant velocity, so that he can capture the bullet easily and put in his pocket

 

[Pommie]

A man is in a row boat that he rows at 4kmh, he's rowing up river and the river is flowing at 1.5kmh. His hat is beside him and it blows off the boat without him noticing. He finally notices that his hat is missing after 15 minutes and immediately turns the boat around to go retrieve his hat. How long does it take for him to catch up with his hat.

And, no, this is not going off topic.

Mike.

 

[KeepItSimpleStupid]

The hat moved s = (1.5kmh/0.250 h) km

he rows at 4 km/h or 0.25 h/km

s km * 0.25 h/km = 1.5 hr to retrieve the hat.

Am I right?

I liked the way things cancelled. Always do dimensional analysis on your answer. You do have to assume something: and that is the 4 kmh is independent of which way he is paddling. That's why i hate these problems.

 

[Pommie]

The hat moved s = (1.5kmh/0.250 h) km

he rows at 4 km/h or 0.25 h/km

s km * 0.25 h/km = 1.5 hr to retrieve the hat.

Am I right?

Nope, think relatively.

Edit, hint, The answer is the same even if you change any/both speeds.

Mike.

 

[ericgibbs]

hi transistor,
How ever fast the bullet leaves the barrel and travels thru the air, gravity will still act on the bullet at 9.81m/ss.

So the bullet will not follow the plane it will fall, curving down towards the ground under the plane.

Just watch a WW2 air combat film where tracer bullets are used.

 

[Mickster]

A man is in a row boat that he rows at 4kmh, he's rowing up river and the river is flowing at 1.5kmh. His hat is beside him and it blows off the boat without him noticing. He finally notices that his hat is missing after 15 minutes and immediately turns the boat around to go retrieve his hat. How long does it take for him to catch up with his hat.
And, no, this is not going off topic.

Mike.

If it's in the wording Mike, he never catches up to it because it doesn't mention him rowing after the boat is turned around....