Question

I am a 42 year old software engineer trying to teach myself physics - so please excuse the stupid questions. :)

My question is - If I am in a plane traveling at 500MPH and I toss a ball into the air, why doesn't ball going flying past my head at 500 MPH once it is tossed up. It seems to me that if I threw a ball in the air and then started running - the ball would not follow me as it seems to in the plane. Thanks!

Answer 1

The fact that we are in a vessel travelling at 500MPH means that we have a horizontal velocity of 500MPH also. However, it doesn't feel like it because relative to the vessel, we have no differences in velocity.

Thus when the ball is released, it will also have a horizontal velocity of 500MPH, together with your vertical velocity provided by your throw.

Thus, as the differences in velocity between you and the ball is the same, it will not be displaced.

Answer 2

Relativity:

Case 1:

I am travelling in a car at 10kmh. I observe another car travelling beside me at 10kmh.
The other car does not seem to be moving forward or moving backward relative to us.
No difference in velocity = perceived distance is same

Case 2:
I am travelling in a car at 10kmh. I observe another car travelling beside me at 100kmh.
The other car seems to be moving forward relative to me.
Difference in velocity = perceived distance is increasing

Answer 3

ok - I think I get it. So in the case where I throw the ball in the air then run, the ball's horizontal velocity is the same as the earth, which was the same as mine at the moment I released it. However, once I started running, my horizontal velocity changed but the ball's did not.

So now my question is - how can I predict what the ball will do if I throw it WHILE running? What establishes horizontal velocity in this case? Thanks!

Answer 4

it depends on the angle at which you throw the ball buddy.. just remember this

if you throw the ball STRAIGHT UP.. (verically up), then its horizontal velocity will NOT CHANGE.. which means

a) if you throw it up when you are at rest (with respect to earth) then the balls horizontal velocity was also zero, and hence after you throw up, the ball will still have no horizontal veolcity . and so if you now start running the ball won't follow you

b) if you throw up when you are already running, you see the ball already has an initial horiztontal velocity, and thus when you throw up, it ll continue to move with the same horizontal velocity (remember the horizontal velocity won't change) and hence it ll follow you and you ll be able to catch it back (provided you don't change your running speed)



if you throw the ball at an angle, then the horiztonal velocity WILL change depending on the angle at which you threw it..

if you are interested in this .. this part of physics is called as PROJECTILE motion and 2D kinematics.. its very veyr very interesting.. but you need the basic knowledge of vectors :) :) :) :).. all the best... !!

Answer 5

Thanks so much for the reply. I will definitely start digging in this area. Here is another thing that I was thinking about that seemed counterintuitive. Say that I am flying in a plane that is travelling at 600 MPH, and I am at the ceiling height. I drop the ball, it should fall straight down, right? Now say that I have the same exact scenario, except I stick my hand outside the plane window and let go. It "feels" like the ball would go flying back away from my hand. I am assuming that it would due to resistance of the air outside the window. If that is true then - would it mean that dropping a ball out of a moving object (in a vacuum) would have the ball staying at your horizontal velocity, while it falls? This seems like black magic to me. :)

Thanks!

Answer 6

An object in motion stays in motion unless some force acts to oppose that motion. You can decompose the motion of the dropped object into orthogonal component, one of which is affected by gravity, and one of which isn't (the horizontal component, which seems like black magic to you). In real life, you've got drag forces and so on acting on the bomb you've dropped, so the horizontal component changes, and some involved calculation is required to find the precise spot at which the aircraft should drop the bomb so that it ends up on the target. Usually, it isn't right over the target!

Answer 7

Hi! I just read your last post. You're right! It feels that way rightfully. I would think that from watching TV!

So, a few things:

I saw someone bringing up relativity. It's a good way to think, after you get some practice with it!

I strongly encourage looking at Newton's Laws, if you haven't already!

When you're on the airplane, traveling 500 MPH relative to the ground, that ball is moving with it, 500 MPH relative to ground, just like you! Throwing it up doesn't change that part of the ball's speed, and so it stay right with you.

When you drop it out of the airplane, you're right. You are going 600 MPH relative to ground, but the air might be still, a.k.a. at rest with the ground. Then the ball is going at the air at 600 MPH! It would be just like a 600 MPH wind on the ball, if you think of the ball as being still (or at rest).

And you continue to be right, as you say that the ball would stay with you if you dropped it in a vacuum!