|
 |
| Rank | Posts | Team |
| Player Coach | 919 | No
Team
Selected |
| Joined | Service | Reputation |
| May 2006 | 19 years | |
| Online | Last Post | Last Page |
| Aug 2013 | Jul 2011 | LINK |
| Milestone Posts |
|
| Milestone Years |
|
|
| Location |
|
| Signature |
|
TO BE FIXED |
|
| Quote J. Willard Gibbs="J. Willard Gibbs"Ignoring air resistance!
 '"
Which would cause a force on the ball, and as I said, the mass only effects the force, so I took that into account |
|
|
| Rank | Posts | Team |
| Player Coach | 978 | No
Team
Selected |
| Joined | Service | Reputation |
| May 2009 | 16 years | |
| Online | Last Post | Last Page |
| Feb 2012 | Feb 2012 | LINK |
| Milestone Posts |
|
| Milestone Years |
|
|
| Location |
|
| Signature |
|
TO BE FIXED |
|
|
Quote Wheres My Shirt="Wheres My Shirt"Which would cause a force on the ball, and as I said, the mass only effects the force, so I took that into account
'"
"Mass would have no effect on speed, direction, or the path of the ball"
It's not as straightforward as you might think; if the two balls have the same shape and velocity at release, they don't necessarily have the same trajectory ...
Let's ignore gravity and just look at the air resistance - the force from that air resistance is proportional to the velocity squared (roughly speaking):
F = kv^2 (k is some friction factor)
We're expecting the force due to air resistance to be the same on both balls, as it only depends on the shape of the ball and the velocity. As we all know, F = ma, and so;
kv^2 = ma
kv^2 = m d/dt v
or, another way,
k (dr/dt)^2 = m d^r/dt^2
So we see that how the velocity of the ball changes in the face of air resistance contains a term dependent on the mass of the ball.
I suspect that the mass of the ball is therefore significant in the case of 2 otherwise identical balls thrown at the same speed in the presence of air resistance. I think the trajectories may well be different, but I've not bothered to plot any of them!
Edit - rather than bothering to solve the equations of motion numerically, I used some Google-fu and came up with this:
jersey.uoregon.edu/vlab/Cannon/
which I think demonstrates the problem. Click the drag on button, and fire the cannon. then only change the density of the projectile, and try again! |
|
Quote Wheres My Shirt="Wheres My Shirt"Which would cause a force on the ball, and as I said, the mass only effects the force, so I took that into account
'"
"Mass would have no effect on speed, direction, or the path of the ball"
It's not as straightforward as you might think; if the two balls have the same shape and velocity at release, they don't necessarily have the same trajectory ...
Let's ignore gravity and just look at the air resistance - the force from that air resistance is proportional to the velocity squared (roughly speaking):
F = kv^2 (k is some friction factor)
We're expecting the force due to air resistance to be the same on both balls, as it only depends on the shape of the ball and the velocity. As we all know, F = ma, and so;
kv^2 = ma
kv^2 = m d/dt v
or, another way,
k (dr/dt)^2 = m d^r/dt^2
So we see that how the velocity of the ball changes in the face of air resistance contains a term dependent on the mass of the ball.
I suspect that the mass of the ball is therefore significant in the case of 2 otherwise identical balls thrown at the same speed in the presence of air resistance. I think the trajectories may well be different, but I've not bothered to plot any of them!
Edit - rather than bothering to solve the equations of motion numerically, I used some Google-fu and came up with this:
jersey.uoregon.edu/vlab/Cannon/
which I think demonstrates the problem. Click the drag on button, and fire the cannon. then only change the density of the projectile, and try again! | |
|
|
|
|
|
| Rank | Posts | Team |
| Club Owner | 10000 | No
Team
Selected |
| Joined | Service | Reputation |
| Feb 2004 | 21 years | |
| Online | Last Post | Last Page |
| Dec 2020 | Nov 2020 | LINK |
| Milestone Posts |
|
| Milestone Years |
|
|
| Location |
|
| Signature |
|
TO BE FIXED |
|
|
Quote J. Willard Gibbs="J. Willard Gibbs"icon_biggrin.gif
"Mass would have no effect on speed, direction, or the path of the ball"
It's not as straightforward as you might think; if the two balls have the same shape and velocity at release, they don't necessarily have the same trajectory ...
Let's ignore gravity and just look at the air resistance - the force from that air resistance is proportional to the velocity squared (roughly speaking):
F = kv^2 (k is some friction factor)
We're expecting the force due to air resistance to be the same on both balls, as it only depends on the shape of the ball and the velocity. As we all know, F = ma, and so;
kv^2 = ma
kv^2 = m d/dt v
or, another way,
k (dr/dt)^2 = m d^r/dt^2
So we see that how the velocity of the ball changes in the face of air resistance contains a term dependent on the mass of the ball.
I suspect that the mass of the ball is therefore significant in the case of 2 otherwise identical balls thrown at the same speed in the presence of air resistance. I think the trajectories may well be different, but I've not bothered to plot any of them!
Edit - rather than bothering to solve the equations of motion numerically, I used some Google-fu and came up with this:
jersey.uoregon.edu/vlab/Cannon/
which I think demonstrates the problem. Click the drag on button, and fire the cannon. then only change the density of the projectile, and try again!'"
Very handy little tool that. The RFL should invest in one to demonstrate passing! 
The factors could be velocity, angle of release, wind resistance and ball size (well there's a size 3, 4 and 5 ball isn't there!). That'd be good in their resources section!
That tool shows that I am right that the weight matters, but wrong that it is because of momentum (taking the drag out means the cannon ball still travels in the same trajectory regardless of density).
What is it the mass of the player then? Or does the ball not travel forwards due to momentum, but due to something else? Wish this thread had been this time last year when I was doing the module as all the notes would be right in front of me! |
|
Quote J. Willard Gibbs="J. Willard Gibbs"icon_biggrin.gif
"Mass would have no effect on speed, direction, or the path of the ball"
It's not as straightforward as you might think; if the two balls have the same shape and velocity at release, they don't necessarily have the same trajectory ...
Let's ignore gravity and just look at the air resistance - the force from that air resistance is proportional to the velocity squared (roughly speaking):
F = kv^2 (k is some friction factor)
We're expecting the force due to air resistance to be the same on both balls, as it only depends on the shape of the ball and the velocity. As we all know, F = ma, and so;
kv^2 = ma
kv^2 = m d/dt v
or, another way,
k (dr/dt)^2 = m d^r/dt^2
So we see that how the velocity of the ball changes in the face of air resistance contains a term dependent on the mass of the ball.
I suspect that the mass of the ball is therefore significant in the case of 2 otherwise identical balls thrown at the same speed in the presence of air resistance. I think the trajectories may well be different, but I've not bothered to plot any of them!
Edit - rather than bothering to solve the equations of motion numerically, I used some Google-fu and came up with this:
jersey.uoregon.edu/vlab/Cannon/
which I think demonstrates the problem. Click the drag on button, and fire the cannon. then only change the density of the projectile, and try again!'"
Very handy little tool that. The RFL should invest in one to demonstrate passing!
The factors could be velocity, angle of release, wind resistance and ball size (well there's a size 3, 4 and 5 ball isn't there!). That'd be good in their resources section!
That tool shows that I am right that the weight matters, but wrong that it is because of momentum (taking the drag out means the cannon ball still travels in the same trajectory regardless of density).
What is it the mass of the player then? Or does the ball not travel forwards due to momentum, but due to something else? Wish this thread had been this time last year when I was doing the module as all the notes would be right in front of me! | |
|
|
|
|
| Rank | Posts | Team |
| Player Coach | 919 | No
Team
Selected |
| Joined | Service | Reputation |
| May 2006 | 19 years | |
| Online | Last Post | Last Page |
| Aug 2013 | Jul 2011 | LINK |
| Milestone Posts |
|
| Milestone Years |
|
|
| Location |
|
| Signature |
|
TO BE FIXED |
|
| Quote J. Willard Gibbs="J. Willard Gibbs"icon_biggrin.gif
So we see that how the velocity of the ball changes in the face of air resistance contains a term dependent on the mass of the ball.
'"
It does, but I also said that the mass only effects the required force, the part you quoted was turning a bit of a blind eye to that - the fact air resistance causes a force is pretty meaningless in a theoretical (and tedius) sense - between the ball hitting each particle of air the mass would have no effect on the speed, direction, or path. A force causing balls of different masses to decelerate at different rates is not contrary to what I intially stated - indeed it is Newton's 2nd law.
Essentially, air resistance is a force and so mass would effect that. I said that.
The mass of the player is thoroughly irrelevant. If, for example, the player dropped the ball vertically as he ran forward, the ball would have gained its forward velocity due to the initial force required to accelerate the player (and ball) to that velocity. Once at that velocity it will maintain it forever unless other forces are applied. |
|
|
| Rank | Posts | Team |
| Club Owner | 10000 | No
Team
Selected |
| Joined | Service | Reputation |
| Feb 2004 | 21 years | |
| Online | Last Post | Last Page |
| Dec 2020 | Nov 2020 | LINK |
| Milestone Posts |
|
| Milestone Years |
|
|
| Location |
|
| Signature |
|
TO BE FIXED |
|
| Quote Wheres My Shirt="Wheres My Shirt"The mass of the player is thoroughly irrelevant. If, for example, the player dropped the ball vertically as he ran forward, the ball would have gained its forward velocity due to the initial force required to accelerate the player (and ball) to that velocity. Once at that velocity it will maintain it forever unless other forces are applied.'"
Right, so what we've learned here is that...
Momentum, i.e. mass x velocity, isn't relevant to why the ball travels forward.
Mass is only relevant in relation to the ball, and that only matters in relation to forces acting upon it (i.e. the player, air resistance and gravity).
Velocity is the only important factor in why the ball travels forward. That is, the velocity of the player in a given direction is transferred to the ball at the time of release, and it's path will be defined by that in conjunction with: the angle of release and the force applied to the ball at that angle of release (as well as the forces of gravity and air resistance).
So really, momentum appears to have absolutely nothing to do it. Stevo should rename it to a more accurate "transferable velocity" rule! |
|
|
|
| Rank | Posts | Team |
| Club Coach | 7152 | No
Team
Selected |
| Joined | Service | Reputation |
| Jan 2005 | 20 years | |
| Online | Last Post | Last Page |
| Dec 2020 | Jun 2020 | LINK |
| Milestone Posts |
|
| Milestone Years |
|
|
| Location |
|
| Signature |
|
TO BE FIXED |
|
| Seriously though, you all need to get laid.
Or have a damn good monkey spank.
 |
|
|
| Rank | Posts | Team |
| Player Coach | 978 | No
Team
Selected |
| Joined | Service | Reputation |
| May 2009 | 16 years | |
| Online | Last Post | Last Page |
| Feb 2012 | Feb 2012 | LINK |
| Milestone Posts |
|
| Milestone Years |
|
|
| Location |
|
| Signature |
|
TO BE FIXED |
|
| What Wellsy said on the last page was actually correct:
Quote Wellsy="Wellsy"Basically, if two people were throwin two different weighted balls in the same direction at the same velocity they would flow on different paths due to the momentum being different'"
But you didn't think so:
Quote Wellsy="you"Not quite - even though the heavier ball would require more force to get it to the same velocity, it would still follow the same path as the lighter ball'"
I just pointed out that your refutation was only valid in the case of no air resistance. Your references to the force required was purely i the context of getting the ball up to that velocity as you passed it, not what happened afterwards:
Quote Wellsy="you"Mass would have no effect on speed, direction, or the path of the ball under any non-relativistic circumstances'"
Which is not true in the case of air resistance being present. |
|
|
| Rank | Posts | Team |
| Club Owner | 10000 | No
Team
Selected |
| Joined | Service | Reputation |
| Feb 2004 | 21 years | |
| Online | Last Post | Last Page |
| Dec 2020 | Nov 2020 | LINK |
| Milestone Posts |
|
| Milestone Years |
|
|
| Location |
|
| Signature |
|
TO BE FIXED |
|
|
|
|
|
|
| Rank | Posts | Team |
| Player Coach | 919 | No
Team
Selected |
| Joined | Service | Reputation |
| May 2006 | 19 years | |
| Online | Last Post | Last Page |
| Aug 2013 | Jul 2011 | LINK |
| Milestone Posts |
|
| Milestone Years |
|
|
| Location |
|
| Signature |
|
TO BE FIXED |
|
| Quote Wellsy13="Wellsy13"So really, momentum appears to have absolutely nothing to do it. Stevo should rename it to a more accurate "transferable velocity" rule!'"
Absolutely, momentum would only really apply in a perfect elastic reaction - whereby the momentum of the player is transferred to the ball. Considering the player has about 500 kgm/s, that would mean a player would need to throw the ball at about mach 3 for momentum to have any application. |
|
|
| Rank | Posts | Team |
| Club Coach | 7152 | No
Team
Selected |
| Joined | Service | Reputation |
| Jan 2005 | 20 years | |
| Online | Last Post | Last Page |
| Dec 2020 | Jun 2020 | LINK |
| Milestone Posts |
|
| Milestone Years |
|
|
| Location |
|
| Signature |
|
TO BE FIXED |
|
| Quote Wellsy13="Wellsy13"And I suppose you're getting it as you type!
'"
I'm in post-coital internet mode. As in, she's up earlier than me so she's asleep.
Quote Wellsy13="Wellsy13"Did nobody tell you that chicks dig an educated bloke
'"
I'm educated. I can count to 120 before I finish, roll over and go to sleep. |
|
|
| Rank | Posts | Team |
| Club Owner | 10000 | No
Team
Selected |
| Joined | Service | Reputation |
| Feb 2004 | 21 years | |
| Online | Last Post | Last Page |
| Dec 2020 | Nov 2020 | LINK |
| Milestone Posts |
|
| Milestone Years |
|
|
| Location |
|
| Signature |
|
TO BE FIXED |
|
| Quote Cronus="Cronus"I'm educated. I can count to 120 before I finish, roll over and go to sleep.'"
That's quite impressive! I get bored after about 22 |
|
|
|
| Rank | Posts | Team |
| Player Coach | 919 | No
Team
Selected |
| Joined | Service | Reputation |
| May 2006 | 19 years | |
| Online | Last Post | Last Page |
| Aug 2013 | Jul 2011 | LINK |
| Milestone Posts |
|
| Milestone Years |
|
|
| Location |
|
| Signature |
|
TO BE FIXED |
|
| Quote J. Willard Gibbs="J. Willard Gibbs"
I just pointed out that your refutation was only valid in the case of no air resistance. Your references to the force required was purely i the context of getting the ball up to that velocity as you passed it, not what happened
'"
Not true, I actually changed my wording so that that would not be the case - "mass would only effect the required force to get it to that speed and in that direction".
Just because I didn't make clear what was applying the force doesn't change the fact I didn't exclude air resistance. |
|
|
|
|
|
'"
