Think you pretty much answer your own question there...

Could we please stop talking about the 'momentum' rule. The player's momentum is irrelevant. The quantity that affects the trajectory of the ball is his velocity.

Momentum cannot be ignored when passing a ball whilst on the run. It's simple physics.

If two players passed a ball in the same direction from the same point at the same velocity, but one player was running and the other was static, they wouldn't end up in the same place.

Momentum is mass times velocity - for the purposes of the discussion, they're pretty interchangable.

I am pretty surprised Boots 'n' All have never done a feature on this, considering Stevo is always harking on about it, as well as the RFL's connections with Carnegie (who have some very good biomechanics facilities).

All it would take is a few light-gates to record the speed of the objects involved (i.e. player and ball) and a few cameras to record the "phenomenon" happening (one parallel to the player and on above looking down) and you've got a simple demonstration as to the effects a player running with the ball has on it's path regardless of the direction it was thrown in.

I may email them actually...

Please, for crying out loud, if you've any doubt of the 'momentum' aspect of running and passing, watch this rlVideorl explaining exactly how it works. It's a RU video, but the concept is the same. Some of the passes are a bit iffy but look past that and it should all become clear.

If the link gets removed, look for "Rugby Union "Forward Pass" video".

Simples.

Yeah, I've seen that video before. It's a good experiment badly performed though. Some of them passes are actually released in a forward direction!

I'll further add to that that the "computer simulation" would never occur, as the ball would never travel straight, it would be curved due to acceleration.

Like I say, some of the passes are 'iffy' at best - I certainly wouldn't look at the hands, but then those are Union players.

But for those who are somehow struggling to understand that if you're running and you pass to a player slightly behind you, the ball will actually move forwards from its original start point while still travelling backwards relative to you and the receiver, it's not a bad guide.

"Momentum is mass times velocity - for the purposes of the discussion, they're pretty interchangable''

Do you really believe that if an eighteen-stone prop forward and a ten-stone scrum half are running at the same velocity and they both throw a ball in the same direction at the same speed then the one from the prop forward will follow a different trajectory than the one from the scrum half? The original J. Willard Gibbs would not agree with you.

I'm back for more abuse

All the physics equations so far are incomplete. They all infer that the players body is still facing the opponents line at the point of release. This is never the case. The player usually changes his angle at time of pass and at the same time rotates his upper body towards the direction he intends to pass adding/shifting mass/velocity. Whilst I realise this is what creates the backward force I think we are possible trivialising its impact and certainly defeats the previous argument about throwing a ball from a moving pickup truck.

Wellsy-please get on to boots n all. Would love to see Stevo justyfying himself and Clarkey trying to pretend he understands.

It's simple enough. Think relativity rather than momentum though. That's what the rule book says.

What are you on about? You're the one who saidCould we please stop talking about the 'momentum' rule. The player's momentum is irrelevant. The quantity that affects the trajectory of the ball is his velocity[/i

For any argument you can make with velocity, momentum is just as useful, as the mass of the player and ball remain basically constant during motion.

If a players momentum is irrelevant, then so is his velocity - as that velocity is [idirectly[/i related to momentum, it's just a simple multiplication.

Edit:

Sorry, I'm not trying to be a pain here - you're quite right in pointing out that the "momentum rule" is a bit of a misnomer, and such things are far better dealt with in terms of the velocity.

It's been a while since I did biomechanics so this may be wrong, but I think the mass in question isn't the mass of the player thowing the projectile (i.e. the ball) but the mass of the projectile itself. The player with the ball is just adding velocity in a given direction to the ball.

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, so your point about the masses of the players themselves would be irrelevant I think (I may need to look that up, but I think it's right).

This doesn't differ from the original point though about players running at different velocities (i.e. one being static and one being on the move) as obviously the velocity would be different and the mass the same, thus a different path.

We aren't abusing you (well, I aren't anyways!) so don't worry! All disagreements don't have to be abusive!

They don't infer anything about the bodies direction, they just infer the velocity given by the body to the ball in a given direction. The body may change which way it is facing, but the direction the body is going in is still the same. The velocity may change due to turning, but the fact that there is velocity there in the given direction still has an affect on the direction the ball will travel in. If you ran forward with a ball and turned the body and passed, the ball will travel in a different direction to if you stood still in the exact same position as you threw the ball.

Perhaps a better example of this would be if you ran at the exact same speed on a treadmill and threw the ball in the same direction. The ball would not travel forward as the velocity would be zero (despite running, you aren't actually moving, thus the ball will be getting no extra forward velocity and thus not effecting its path).

I've emailed Boots N All last night. When I get home I'll post the email on here if I have time. Would be a very interesting segment, mainly to see if they can get it right!

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. Mass would have no effect on speed, direction, or the path of the ball under any non-relativistic circumstances, regardless of how fast the inertial frame of reference (the passer) was moving - mass would only effect the required force to get it [ito[/i that speed and in that direction.