Can a ball get faster as it travels through the air?

keanooo · 04-12-2011 2:07pm #1

I watched Socrates' goal against Russia today (http://www.youtube.com/watch?v=H8Qlsw8FtIg) and was wondering if it is possible for a ball to accelerate after it has been struck? I've read match-reports refer to this also but it would appear to defy the laws of physics.

EdenHazard · 04-12-2011 2:23pm

no just back then they were more in awe of things

3hn2givr7mx1sc · 04-12-2011 2:27pm

I'd say it just the dodgy camera making it look like that.

EdenHazard wrote: »

no just back then they were more in awe of things

What?

Big Pussy Bonpensiero · 04-12-2011 2:33pm

No.

helimachoptor · 04-12-2011 2:34pm

Nope is the short and long answer.

recyclebin · 04-12-2011 2:35pm

Technically yes. It's called gravity.

oconnon9 · 04-12-2011 2:35pm

Yeah of course they accelerate after being struck. At the moment of impact its speed is 0mph.. It picks up speed to a certain point and slows down again.

Socrates goal is an example of a shot which had probably just about reached this point by the time the net stopped it

keanooo · 04-12-2011 2:37pm

recyclebin wrote: »

Technically yes. It's called gravity.

I meant in the horizonal plane. I'm not talking about someone kicking a ball from the sky downwards.

Dotrel · 04-12-2011 2:41pm

keanooo wrote: »

I watched Socrates' goal against Russia today (http://www.youtube.com/watch?v=H8Qlsw8FtIg) and was wondering if it is possible for a ball to accelerate after it has been struck? I've read match-reports refer to this also but it would appear to defy the laws of physics.

That's just an optical illusion caused by the fact that camera is relatively fixed position as Socrates dribbles and kicks the ball, but then violently pans left following the shot effectively "adding" to the apparent speed of the ball.

You get that sort of camera work less and less these days thanks to the new picture format. 16:9 presentation has really done wonders in terms of presenting more of a match on tv vs the old style 4:3. I watched the 1972 European cup final recently and it was really hard to even follow the game such was the camera-work.

To answer your question, as has been pointed out the ball does go from 0kph to a certain speed when it is kicked, but I don't see how a ball could continuously speed up over its flight as no additional force is being added to it after it has been kicked. It should slow down over a distance of 20-30 yards.

keanooo · 04-12-2011 3:01pm

Dotrel wrote: »

That's just an optical illusion caused by the fact that camera is relatively fixed position as Socrates dribbles and kicks the ball, but then violently pans left following the shot effectively "adding" to the apparent speed of the ball...

That should make the ball appear slower, not faster, after he shoots.

If the camera were fixed we would have seen it pick up even more speed.

Dotrel · 04-12-2011 3:05pm

keanooo wrote: »

That should make the ball appear slower, not faster, after he shoots.

If the camera were fixed we would have seen it pick up even more speed.

Yeah actually you have a point there. On second look it seems as tho the camera whips left quickly and then slows down again once it frames the USSR goal. I think the subsequent slowing down is what is causing the illusion of the ball speeding up at the end. Again, I'm open to correction on that.

keanooo · 04-12-2011 3:14pm

Dotrel wrote: »

Yeah actually you have a point there. On second look it seems as tho the camera whips left quickly and then slows down again once it frames the USSR goal. I think the subsequent slowing down is what is causing the illusion of the ball speeding up at the end. Again, I'm open to correction on that.

Actually if you go through it frame by frame the cameraman starts panning at a normal speed, but as the ball gains pace he has to pan left faster and faster. He end up overcompensating... hence the sudden halt.

Dotrel · 04-12-2011 3:17pm

The entire game is here
http://www.youtube.com/watch?v=5DxYrisK6yg&t=1h15m40s

I was hoping they might have an alternative angle from behind the goal or something so that we could get a better look it but they don't appear to have even had multi angle replays back then.

the untitled user · 04-12-2011 3:49pm

Everyone is forgetting the obvious answer: a good old gust of wind

_blank_ · 04-12-2011 4:00pm

When Man Utd played Crystal Palace during the week and Darren Ambrose, the commentators were saying the ball was still picking up speed when it was going in the net.

Pro. F · 04-12-2011 4:25pm

No. Newton's first law of motion (from wikipedia):

The
velocity of a body remains constant unless the body is acted upon by an external force.

So after the ball leaves his foot the only external forces acting on it are wind resistance and gravity. The spin makes a ball dip and swerve by affecting the wind resistance, but that's not going to pull it forward.

oconnon9 wrote: »

Yeah of course they accelerate after being struck. At the moment of impact its speed is 0mph.. It picks up speed to a certain point and slows down again.

Socrates goal is an example of a shot which had probably just about reached this point by the time the net stopped it

You're looking at it wrong. All the forward acceleration is done when his foot is in contact with the ball and it starts to decelerate as soon as it leaves his foot. The forward deceleration just isn't noticeable over that distance so the affect of whatever the optical illusion is is really strong.

Eathrin · 04-12-2011 4:31pm

Pro. F wrote: »

No. Newton's first law of motion (from wikipedia):

The
velocity of a body remains constant unless the body is acted upon by an external force.

So after the ball leaves his foot the only external forces acting on it are wind resistance and gravity. The spin makes a ball dip and swerve by affecting the wind resistance, but that's not going to pull it forward.

You're looking at it wrong. All the forward acceleration is done when his foot is in contact with the ball and it starts to decelerate as soon as it leaves his foot. The forward deceleration just isn't noticeable over that distance so the affect of whatever the optical illusion is is really strong.

Gravity only acts in the downward direction, the horizontal speed is unaffected. YES the ball can speed up if the forces moving in the same direction (i.e. Wind)
are greater than those opposing it (i.e. Friction/air resistance).

04-12-2011 4:38pm

Pro. F wrote: »

No. Newton's first law of motion (from wikipedia):

The
velocity of a body remains constant unless the body is acted upon by an external force.

So after the ball leaves his foot the only external forces acting on it are wind resistance and gravity. The spin makes a ball dip and swerve by affecting the wind resistance, but that's not going to pull it forward.

You're looking at it wrong. All the forward acceleration is done when his foot is in contact with the ball and it starts to decelerate as soon as it leaves his foot. The forward deceleration just isn't noticeable over that distance so the affect of whatever the optical illusion is is really strong.

Any change in velocity is an acceleration. Deceleration isn't used in Physics.

Acceleration is a change in velocity, not speed.

So the ball could be slowing down in speed yet still accelerating.

Pro. F · 04-12-2011 4:42pm

rarnes1 wrote: »

Any change in velocity is an acceleration. Deceleration isn't used in Physics.

Acceleration is a change in velocity, not speed.

So the ball could be slowing down in speed yet still accelerating.

Semantics. I used the word deceleration for clarity because this is a conversation in English about the physics of footballs, not a conversation in physics about footballs.

Pro. F · 04-12-2011 4:49pm

Cian A wrote: »

Gravity only acts in the downward direction, the horizontal speed is unaffected.

Yeah, I didn't say otherwise.

Cian A wrote: »

YES the ball can speed up if the forces moving in the same direction (i.e. Wind)
are greater than those opposing it (i.e. Friction/air resistance).

True. But we do see this happening (or appearing to happen) when there is no wind so I'm going with something other than wind.

Actually does anybody know if a change in spin is a change in velocity? If it is not then the ball could be increasing spin over its flight (because of the rubber twisting and untwisting or something), so reducing drag and increasing speed.

keanooo · 04-12-2011 4:50pm

Cian A wrote: »

YES the ball can speed up if the forces moving in the same direction (i.e. Wind)
are greater than those opposing it (i.e. Friction/air resistance).

"Cian", in the cases we are discussing, free-kicks, belters at goal etc. the ball is moving too fast for the wind to increase it's speed.

Eathrin · 04-12-2011 5:22pm

Pro. F wrote: »

Yeah, I didn't say otherwise.

True. But we do see this happening (or appearing to happen) when there is no wind so I'm going with something other than wind.

Actually does anybody know if a change in spin is a change in velocity? If it is not then the ball could be increasing spin over its flight (because of the rubber twisting and untwisting or something), so reducing drag and increasing speed.

Fair enough.

I'd imagine it could, we do see it changing velocity mid flight side to side so quite possibly the spin can affect the speed moving forward.

keanooo wrote: »

"Cian", in the cases we are discussing, free-kicks, belters at goal etc. the ball is moving too fast for the wind to increase it's speed.

That's ridiculous, maybe you don't notice it but the wind absolutely does change velocity.

04-12-2011 5:27pm

Pro. F wrote: »

Semantics. I used the word deceleration for clarity because this is a conversation in English about the physics of footballs, not a conversation in physics about footballs.

Fair enough

keanooo · 04-12-2011 5:32pm

Cian A wrote: »

That's ridiculous, maybe you don't notice it but the wind absolutely does change velocity.

It can slow it down. It can't speed it up.

amacachi · 04-12-2011 5:32pm

Cian A wrote: »

Fair enough.

I'd imagine it could, we do see it changing velocity mid flight side to side so quite possibly the spin can affect the speed moving forward.

That's ridiculous, maybe you don't notice it but the wind absolutely does change velocity.

If a ball is moving at 70mph then a 70mph gust from behind would only let it maintain that speed as it eliminates(ish) friction, it requires a windspeed greater than the speed of the ball to increase the speed of the ball.

stovelid · 04-12-2011 5:36pm

Andy Gray would know.

Pro. F · 04-12-2011 5:37pm

Cian A wrote: »

I'd imagine it could, we do see it changing velocity mid flight side to side so quite possibly the spin can affect the speed moving forward.

It swerves because of spin and spin reduces drag which allows a higher speed. But for the spin to increase speed over the flight the spin would need to be increasing, not remaining constant. Spin can't increase if it is a type of velocity (according to Newton's first law), but I can't find on the net whether spin is a type of velocity or not.

Cian A wrote: »

That's ridiculous, maybe you don't notice it but the wind absolutely does change velocity.

If it's a belter of a shot and the ball is moving at, what, something like more than 60mph, then the wind would have to be moving faster in order to accelerate the ball forward. Gusts of wind over 60mph in a stadium during a game would be unheard of I would have thought.

Eathrin · 04-12-2011 5:42pm

amacachi wrote: »

If a ball is moving at 70mph then a 70mph gust from behind would only let it maintain that speed as it eliminates(ish) friction, it requires a windspeed greater than the speed of the ball to increase the speed of the ball.

Pro. F wrote: »

It swerves because of spin and spin reduces drag which allows a higher speed. But for the spin to increase speed over the flight the spin would need to be increasing, not remaining constant. Spin can't increase if it is a type of velocity (according to Newton's first law), but I can't find on the net whether spin is a type of velocity or not.

If it's a belter of a shot and the ball is moving at, what, something like more than 60mph, then the wind would have to be moving faster in order to accelerate the ball forward. Gusts of wind over 60mph in a stadium during a game would be unheard of I would have thought.

Why would wind speed have to be greater than the ball's speed? They are moving in the same direction so the velocities combine(ish). Correct me if I'm wrong but we don't know exactly how much friction the air resistance exerts on the ball either. So a greater speed of wind than the ball is not necessarily required.

amacachi · 04-12-2011 5:48pm

Cian A wrote: »

Why would wind speed have to be greater than the ball's speed? They are moving in the same direction so the velocities combine(ish). Correct me if I'm wrong but we don't know exactly how much friction the air resistance exerts on the ball either. So a greater speed of wind than the ball is not necessarily required.

If the ball is moving in air in the same direction and at the same speed then all that does is eliminate friction. Once the ball leaves the foot (other than gravity) the only force acting on the ball is friction. Put a ball into a stream and once it gets to the speed of the stream then that's as fast as it goes because there's no extra force being added. It's the same with a ball, if there's a headwind then friction is greater than with no wind. If there's a slight tailwind there's still some friction, a tailwind at the same speed as the ball and there's "no friction", a tailwind faster than the ball and the ball will speed up.

Pro. F · 04-12-2011 5:57pm

Cian A wrote: »

Why would wind speed have to be greater than the ball's speed? They are moving in the same direction so the velocities combine(ish). Correct me if I'm wrong but we don't know exactly how much friction the air resistance exerts on the ball either. So a greater speed of wind than the ball is not necessarily required.

Because the forward moving air can't act on the ball in that direction if the ball is already moving faster than the air is. So the only affect from the air would be resistance. Presumably less resistance than if the air was still.

It's like how a foot moving at 40mph trying to push a ball forward that is already moving at 80 mph. The foot would never catch up with the ball to push it forward. That's the way it seems to me anyway.

Eathrin · 04-12-2011 6:09pm

So if an object is accelerating downwards faster than gravity, gravity does not affect it? Essentially this is comparable as acceleration is a vector after all.
I can't actually find an answer to verify this at all.

amacachi · 04-12-2011 6:18pm

Cian A wrote: »

So if an object is accelerating downwards faster than gravity, gravity does not affect it? Essentially this is comparable as acceleration is a vector after all.
I can't actually find an answer to verify this at all.

NO! AGH!

Friction is variable while gravity isn't. Just forget about gravity, just think about the air that the ball is moving through, that's the only force in the horizontal plane once the ball has left the foot.
If the wind is from behind the ball but slower than the ball then the air resistance will still cause the ball to slow down, but by less than if the air were still. The only time there's no friction (allowing the ball to maintain constant speed) is if the air and ball are moving at the same speed.

The reason space probes can travel so quickly without an additional force is because space is (almost) empty so there's very little air resistance. The air is comparatively thick on earth so there'll always be air resistance. The only way the wind can speed the ball up is if it's faster than the ball and in the same direction.

quarryman · 04-12-2011 6:19pm

This is actually being discussed? Wow.

The answer us no.

Pro. F · 04-12-2011 6:32pm

Cian A wrote: »

So if an object is accelerating downwards faster than gravity, gravity does not affect it? Essentially this is comparable as acceleration is a vector after all.
I can't actually find an answer to verify this at all.

But gravity is a constant. It always acts.

keanooo · 04-12-2011 6:35pm

Cian A wrote: »

So if an object is accelerating downwards faster than gravity, gravity does not affect it? Essentially this is comparable as acceleration is a vector after all.
I can't actually find an answer to verify this at all.

I think at this stage you better leave this discussion to the big boys. Thanks for your contributions, such as they were.

Pro. F · 04-12-2011 6:52pm

keanooo wrote: »

I think at this stage you better leave this discussion to the big boys. Thanks for your contributions, such as they were.

He's only discussing the thing, no harm. I don't think anybody in this thread is completely familiar with all this physics. Google, hazy memories from school and reasoning it out are probably all we can do for now.

IvySlayer · 04-12-2011 7:10pm

https://www.youtube.com/watch?v=IRsPheErBj8

Had to be done

CR 7 · 04-12-2011 7:18pm

keanooo wrote: »

I think at this stage you better leave this discussion to the big boys. Thanks for your contributions, such as they were.

Lol, that's a bit rich coming from you.

IvySlayer · 04-12-2011 7:28pm

Friction would de-accelerate the ball as soon as it starts moving no?

Amirani · 04-12-2011 7:35pm

IvySlayer wrote: »

Friction would de-accelerate the ball as soon as it starts moving no?

Yes. The ball will be moving at its greatest velocity the instant after it's struck, provided no unbalanced external force acts in the direction of travel (i.e. a tailwind).

breadmonkey · 04-12-2011 7:39pm

keanooo wrote: »

I think at this stage you better leave this discussion to the big boys. Thanks for your contributions, such as they were.

Laughable coming from the person who started this thread, thereby implicitly expressing their ignorance of the physics of the situation.

keanooo · 04-12-2011 7:44pm

breadmonkey wrote: »

Laughable coming from the person who started this thread, thereby implicitly expressing their ignorance of the physics of the situation.

The only thing that is laughable* is that there are enough people here to take such a thread seriously.

*other than your wang size of course

breadmonkey · 04-12-2011 7:50pm

keanooo wrote: »

The only thing that is laughable* is that there are enough people here to take such a thread seriously.

*other than your wang size of course

Oh right, you were just testing the rest of us. Spare me.

keanooo · 04-12-2011 7:51pm

Park Ji Sung wrote: »

Lol, that's a bit rich coming from you.

As someone who has a decent collection of accelerating 20 to 25 yards belters - with a team that is currently knocking at the door of our provincial cup semi-final - I think you'll find that I am a well-placed to speak as an authority on the topic.

Eathrin · 04-12-2011 7:58pm

keanooo wrote: »

I think at this stage you better leave this discussion to the big boys. Thanks for your contributions, such as they were.

Ok, I'm finished debating now, I'm not fully convinced either way, I'll leave that at that.

But there's absolutely no need to be so condescending. Are you implying that I am not as smart as you, or as knowledgeable about football? What you said is just plain rude and I wouldn't take that if you said it to my face. I'd like to call you something else too but I'd probably get a banning for it so I'll hold back. Enjoy your thread.

keanooo · 04-12-2011 8:16pm

Cian A wrote: »

Are you implying that I am not as smart as you, or as knowledgeable about football?

As someone who is both a qualified Engineer and whose photo has frequently adorned "The Target" section of The Star, you would not be alone amongst contributors to this thread in being less smart and less knowledgeable about football than myself.

Please don't take it personally.

Amirani · 04-12-2011 8:18pm

keanooo wrote: »

As someone who is both a qualified Engineer and whose photo has frequently adorned "The Target" section of The Star, you would not be alone amongst contributors to this thread in being less smart and less knowledgeable about football than myself.

Please don't take it personally.

Is there much point posting in a discussion forum if you're far more intelligent than everyone else?

keanooo · 04-12-2011 8:31pm

NiallSparky wrote: »

Is there much point posting in a discussion forum if you're far more intelligent than everyone else?

It's of benefit to the other participants of the thread - such as Cian here - whose thoughts and views on the world are clearly in their formative stages...

breadmonkey · 04-12-2011 8:44pm

What are you on about? You clearly didn't understand it yourself and now you put on this offensive attacking other posters to try to disguise your own ignorance. GTFO

keanooo · 04-12-2011 9:09pm

breadmonkey wrote: »

...you put on this offensive attacking other posters to try to disguise your own ignorance...

GTFO

Not everyone is as gratuitously insulting for the same reasons as you are.

bazual · 04-12-2011 9:19pm

I don't know what everyone is ranting on about, the answer is obviously YES....

Can a ball get faster as it travels through the air?

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