what are you doing ?

[Nick]

it can be a little fun to be pedantic - don't take it to seriously.

You do I hope realise the inherent self contradictory nature of that statement.

I ask because it's plain to me that the tennis ball would be subject to extreme initial acceleration and would not be constrained by terminal velocity, whereas the return journey would commence with sedate initial acceleration and be subject to terminal velocity,

Its been some tine since O level physics, but I think that is a bit confused. Once the ball left the area of the muzzle, it was acting as a free moving body with mass and velocity, so momentum. The exchange of kinetic with potential energy would mean that ignoring drag, the flight up and the flight down would be identical, in both cases the only acceleration the ball would have acting on it was that of gravity.

Would be easier to see if the muzzle was not vertical. Assuming the hight above ground of the end of the muzzle could be ignored the flight would be a parabola so equal on the up and down side.

I did try and consider drag, but it was late and I ended up with a very small number for the actual hight. I did find several interesting papers and articles on the physics of tennis ball flight. So it wasn't a wasted journey. Though from Nick(J)'s description its far from a standard ball anyway, so the 0.54 drag coefficient I used was probably out (interestingly seems to be the same as a VW beetle).

This is physics, so tends to concern spherical cows in a vacuum

[ed]

Its been some tine since O level physics

it may be a bit longer for me..Which will be my excuse if I'm wrong.

Once the ball left the area of the muzzle, it was acting as a free moving body with mass and velocity, so momentum. The exchange of kinetic with potential energy would mean that ignoring drag, the flight up and the flight down would be identical, in both cases the only acceleration the ball would have acting on it was that of gravity.

This is the bit I have trouble with. 'In both cases the only acceleration'.....the outward journey is subject to ballistic acceleration, and deceleration. The return journey is only subject to gravitational acceleration(9.81m/s/s). I can't reconcile them being the same.

[Nick]

the outward journey is subject to ballistic acceleration

Not once its left the muzzle I would have thought.

[Nick]

Or to put it another way, it should hit the ground with the same velocity as it left the muzzle. Its got the same mass and its at zero height (WRT the starting point), so zero potential energy. As the total energy will be constant then the kinetic energy at the end must be the same as at the start and given the mass hasn't changed then the velocity will be equal

ballistic acceleration

Maybe my fault, but I don't know what that is, AFAIK, ballistic motion is that of a projectile that is in free flight, ie its not propelling itself, so there is only the acceleration of gravity acting on it.

[jack]

Or to put it another way, it should hit the ground with the same velocity as it left the muzzle. ...

That's true in a vacuum. Not in a thick medium like air...

[Nick]

Or to put it another way, it should hit the ground with the same velocity as it left the muzzle. ...

That's true in a vacuum. Not in a thick medium like air...

Yes, see point about spherical cow.

[ed]

I'm almost certainly wrong, but I can't see why or where....by the way I understand terminal V to be somewhere in the region of 125mph or metric equivalent. I ought to know, I had the very first copy of Nelkon and Parker in SI units, but that number escapes me....I remembered the book though, that ought to count for something....

[pre65]

Would the surface of the dog chewed tennis ball cause the ball to spin whilst in motion (up and down) and if so would that fact have to be factored into the equation ?

[Nick]

Well, I am ignoring drag, so if you are ok with that, then when the ball leaves the barrel its reached its maximum velocity after being accelerated by the pressure behind in. If its going at 200m/s, and it weighs (for convenience) 50g, then it will have a kinetic energy of 200 * 200 * 0.05 * 0.5 or 1000J. If we then convert that 1000J into potential energy, then it will travel 1000 / ( 0.05 * 9.81 ) or 2038m. It will stop at the top (that being the definition of top), then fall 2038m, where it will accelerate to sqrt( 2 * 2038 * 9.81 ) or 200m/s. Which we would expect as all its potential energy will have been converted back to kinetic. And as we are ignoring drag, first law means we can ignore any losses so would expect 200 = 200 (ignoring direction change).

Good place to find what’s been forgotten

https://en.wikipedia.org/wiki/Equations ... lling_body

[Nick]

Would the surface of the dog chewed tennis ball cause the ball to spin whilst in motion (up and down) and if so would that fact have to be factored into the equation ?

In reality its likely to spin anyway, but then it gets a whole lot more complex. But as I said there are lots of papers on the physics of tennis balls if you want to go deeper.

[IslandPink]

....by the way I understand terminal V to be somewhere in the region of 125mph or ....

I think that's for a human. I expect for a tennis ball, which I less dense, it would be a fair bit less.

[Nick]

[Ray P]

it can be a little fun to be pedantic - don't take it to seriously.

You do I hope realise the inherent self contradictory nature of that statement.

I suspect you're demonstrating my point...

Perhaps, for more precision I should have written 'it can be a little fun to act in a pedantic manner - don't take it to seriously'.

[Ray P]

the outward journey is subject to ballistic acceleration

Not once its left the muzzle I would have thought.

Yes, the initial acceleration is whilst the object is in the barrel, which is why high-velocity guns tend to have long barrels. After leaving the barrel the projectile is decelerating due to gravity and drag.

[Nick]

it can be a little fun to be pedantic - don't take it to seriously.

You do I hope realise the inherent self contradictory nature of that statement.

I suspect you're demonstrating my point...

TBH, all you are doing is making it clear you don't understand my sense of humour.

And perhaps the converse.