# Ball that flies with you

1. Apr 19, 2004

### AnthreX

say you have a ball thrower that throws the ball at 100 km/h foward
and you are in a car travelling at 100km/h and you r going parallel to each other would you see the ball flying with you ?

and is it possible to catch it ? and what if you put your hand in front of the ball what would happen ?

2. Apr 19, 2004

### Bob3141592

The ball would seem to hang motionless in space next to you. Actually, since gravity is acting on it, it would appear to fall as if you just dropped it. So to catch it, all you would have to do is to put your hand directly under it, and allow it to fall into your hand.

3. Apr 20, 2004

### Molydood

well, of course you are assuming that the ball remains at constant forward velocity, which in real life it wouldn't; it would decelerate pretty quickly, especially at that speed (air resistance increase with square of speed)

If the car was to allow to decelerate naturally it would do so at a different rate (as it is much heavier and has a different frontal area). The only true way to experience what you say is to either keep the ball and car moving at constant velocity (impossible for the ball, unless it was a guided missile!) or match the balls rate of deceleration in the car (difficult without computer control)

MArtin

4. Apr 27, 2004

### Bob3141592

Well, that's all very true. But, when questions like this are usually asked, especially in introductory physics classes, things like friction and air resistance are usually ignored. Right? Given the nature of the question, I figured the person asking the question was rerlatively unschooled in the subject, and answered accordingly.

Granted, in my answer I should have said "ignoring air rersistence" to be more complete. But lots of complicating secondary factors are omitted without explicitely stating so. For example, are you assumming the ball is being thrown in a strictly east-west direction? If it's being thrown to the north or south, do we have to account for the different velocity of the ground the car travels on? Do we have to state the road is smooth and level? Do we have to say that the substrate the car travels over is uniform, so there are no variations in the local gravitational field? In what direction is the sun shining, so the differential pressure from it's photons can be accounted for? Is the ball rotating? Is the ball perfectly smooth? Etc...

There is a level in physics where all of these effects must be accounted for and addressed. I did not think the original poster was at that level and so tried to provide a simple answer to help them understand the basics. I believe complicating my answer further would have been counterproductive and would only have put up a barrier to understanding physics for the person asking the question. If I was wrong in that estimation, then I apologize.

5. May 9, 2004

### Molydood

well, neither of us know the level of knowledge of the asker, hence two different answers.
hopefully both our answers offered something of interest.
Martin