Does a ball thrown straight up in the air come to a stop before reversing directions and falling back to earth

Question

If the answer is yes, would the same rules apply to a fly (or a rock) hitting a train head on? If the rock (or bug) stops before reversing direction, doesn't that mean that the train stopped as well, even if only for an instant?

Answer 1

Not really. In the case of the thrown ball, it is slowly changing speed all the time. It smoothly slows down, theoretically is stopped for an infinitely short time and smoothly speeds up in the opposite direction (down). In reality, it is always accelerating down at 10 meters per second per second, even while it is still moving up. In the case of the fly, it is flying along at a constant speed, not accelerating or slowing down at all, and suddenly is pushed in the opposite direction. Theoretically, the fly is never stopped in that case, even for an infinitely short time. It simply changes from one speed in one direction to another speed in the opposite direction instantaneously. And theoretically it experiences infinite acceleration in that instant.

But in real life the fly would take some very short time to slow down and reverse direction. It would be "cushioned" by the elasticity of it's own body squishing as it hit the train, assuming it didn't just become a spot on the windshield, and the train's windshield would dimple ever so slightly as the glass bent under the force of impact (VERY slightly) and then rebounded again. The result might be that a few atoms of the windshield might be stopped for a fraction of a second, but they would quickly spring back before the rest of the train even noticed.

Answer 2

Interesting thought.

The ball doesn't come to an abrupt stop. If you measured the speed at which a ball thrown up slows down and reverses, and then plot it on a graph (assuming the verticle axis is velocity and the horizontal axis is time), you'll find it's a perfect parabolic curve resembling a "U" and the bottom tip of the "U" touches the horizontal axis (zero velocity).

If you graphed the speed of a fly hitting a train, however, it would be three lines. It would be flat at until a certain point, then slope upward sharply for a split second (this is when it hits the train), and the flat again much higher up the verticle axis. It would not hit the horizontal axis (zero velocity) at all.

As for the train itself, it would slow down when it hits the fly, but the change in speed would be so incredibly small that no one would ever notice, not even with the most sophisticated tools.

Answer 3

Yes the ball would be stopped in mid-air at a point neither going up or falling down and the only way the train would have this same moment is if the train was stopped by the rock and went in the opposite direction. If the train is still moving forward after it hits the rock then it never came to a stop.

Answer 4

The laws of physice do not permit an object to move in two directions at the same time, therefore there has to be a time between the ball going up and the ball falling down. During this time the only option left is for the ball to be stopped. Milli, micro, nano or pico seconds,it does not matter how long this time is.
For the same reason an object hitting a train and then being driven in the opposite direction by the train has to be stopped for a period of time to allow the reversal to occur. The train itself will not be stopped as the mass of the train will be millions of times greater than the mass of the object, but the speed of the train will be slowed by an amount determined by the ratio of the train s mass and speed to that of the object s mass and speed. This slowing of the train will not occur if the object impacts a flexible part of the train (like a window, sheet metal plate etc.) which can absorb the impact of
the object. In this case the point of impact on the train will stop going forward, be pushed back (to a degree determined by the mass and speed of the object and of the train), stop going back, then go forward again and catch up with the speed of the rest of the train.
If the object hitting the train is another train of equal mass and aerodynamics, and hitting head-on, both trains will stop going forward. Lets assume this happens in a unbreakable tunnel which prevents derailment or the trains being driven up into the air. The huge amount of energy released will blow the two trains back in the directions they came from, to a distance determined by the mass and speed of each of the trains (which in this case we assumed to be equal).

Answer 5

Without more details, the only correct answer ought to be: E. All of the Above If the forces acting upon the ball include atmospheric friction, then 'A'. If the car is travelling reverse, then 'B'. If by "open" you mean that only the doors and windows are unobstructed, then 'C', because the ball thrown straight up would strike the roof of the car and rebound at an angle of opposition equal to the angle of incidence, which would be directly in his hand if the car was on a level surface and the roof was also perfectly level. If by "open" you mean that only the doors and windows are unobstructed and the car had two flat tires on one side or the other, then 'D'.

Answer 6

If the Ball went straight up and there was no wind or anything to affect trajectory then yes is stops before changing directions and falling back.It has to.

As far as the rock or bug hitting the train the train does not stop or even sslow in the smallest bit because of its mass and velocity.

Answer 7

your comparing apples and oranges.

You impart an initial velocity on the ball when you throw it up and gravity acts to decelerate it. At some point this acceleration will cause the velocity equation to yield a zero value, hence stopping in midair.

Your train /fly example is best explained by momentum. Wehn the train and fly hit, the additive momentum of the resulting aggregate is equal to the sum initially. They are moving in opposite directions, so the momentum is subtractive. the aggregate will continue to move in the direction of the initial body with the most momentum, at a speed relative to the new aggregate

mTvT - mFvF = mAvA

Since the fly momentum is << train momentum, little effect will be exhibited.

Answer 8

Yes, a ball thrown straight up in the air stops before it comes back down. The rock does stop fpr a split second, and the train doesn't stop because it has more momentum. You can't really see what happens in a collision. You can only measure its before and after effects. If you look at energy graphs and accleration graphs you could figure this out.

Answer 9

The ball does come to a complete stop before coming down (at the top of the throw) unless it has a spin in which it would continue to spin. But with the bug train issue the bug would not have enough amount of force to stop the train although it would exert a tiny amount of force against the train.

Answer 10

yes it does stop. yes a fly or a rock stops, no the train doesnt stop. for instance pretend the train had no motot but was moving very fast on only momentum the only way it could stop is if the momentum ran out so if it were to stop it wouldn't just stop for an instant but it would stopp completely. this obviously doesn't happen. the train might slow down, but it doesn't stop.

Answer 11

For all intents and purposes, on the up/down axis relative to an observer on earth next to the rock, yes it goes straight up, stops, and comes straight back down. However, the surface of the earth the thrower is standing on is not stationary, the earth is spinning on its axis. So, if an observer not moving along with earth's surface could see the rock thrown, they would see it travel in a parabolic arc. Unless, of course, it was a rock-et and achieved escaped velocity, then it would come back down for a while.