81 replies to this topic

[Wellsy4HullFC]

Well, those that would like the forward pass rule to be only in relation to the pitch and not the players should feast their eyes on this. Conclusive evidence that Leroy Cudjoe's out-the-back-door pass (you can't get any more a backwards pass than that!) was actually forward in relation to the pitch:

Exhibit A & B:




Put them together and look what you get...
Exhibit C:



So, those that would like a "simpler" rule are basically saying that players can't pass when they're running! The most backwards of passes in relation to a player you can do still went forward in relation to the pitch. What a boring game some people must want in order for life to be "simple".

[Wellsy4HullFC]

Just in case you want another angle...





(He's not even caught the ball yet on this picture, and look where he's stood in comparison to the lines on the pitch...)



Conclusive evidence that Cudjoe's pass should have been classed as forward to those that want the "simpler" rule.

In reality, the laws of the game rightly recognise that the ball will travel forwards when a player passes at speed (but wrongly recognises that it is due to "momentum", which is technically not correct. It's due to a player's constant velocity when he passes, not his momentum).

[RidingPie]

I've been watching the NRL and the way the Aussie commentators say it sounds simpler and makes more sense. They say "its got to come backwards out of the hands"

[Wellsy4HullFC]

I've been watching the NRL and the way the Aussie commentators say it sounds simpler and makes more sense. They say "its got to come backwards out of the hands"

That's how Brian Carney and Phil Clarke describe it as well.
Here's the law:

Direction of Pass 1. The direction of a pass is relative to the player making it and not to the actual path relative to the ground. A player running towards his opponents’ goal line may throw the ball towards a colleague who is behind him but because of the thrower’s own momentum the ball travels forward relative to the ground. This is not a forward pass as the thrower has no passed the ball forward in relation to himself. This is particularly noticeable when a running player makes a high, lobbed pass.

After a discussion I had with someone, we agreed that it cannot be because of momentum, so this needs changing.

Momentum = mass * velocity

The mass of the player doesn't affect how far the ball travels forwards. And the mass of the ball is constant, so cannot be affected. The only thing the player can add to the ball is velocity (speed in a given direction), so the rule should really say "because of the thrower's own velocity".

Every body remains in a state of constant velocity unless acted upon by an external unbalanced force. This means that in the absence of a non-zero net force, the center of mass of a body either remains at rest, or moves at a constant velocity.

[Dave T]

Good post Wellsy, and one worth keeping in reserve for the next time people bring up the 'in relation to the pitch' nonsense.

[Lobbygobbler]

He actually catches it in line with where it was passed relative to the pitch!

[RidingPie]

Of course though Newton's First Law of Motion doesn't take in to account Einstein's curved space-time.

Maybe we should call it the Relativity Rule. The pass has to go backwards relative to the person passing it.

[Wellsy4HullFC]

He actually catches it in line with where it was passed relative to the pitch!

On the last picture, he is clearly stood in front of Cudjoe and he hasn't even caught the ball yet!

[JohnM]

That's how Brian Carney and Phil Clarke describe it as well.
Here's the law:



After a discussion I had with someone, we agreed that it cannot be because of momentum, so this needs changing.

Momentum = mass * velocity

The mass of the player doesn't affect how far the ball travels forwards. And the mass of the ball is constant, so cannot be affected. The only thing the player can add to the ball is velocity (speed in a given direction), so the rule should really say "because of the thrower's own velocity".

and given that velocity is a vector and speed is scalar, that covers direction, too.

[tonyXIII]

At the risk of starting a row about maths, I should point out that, AFAIK momentum is a fair description.

The statement "momentum = mas * velocity" is true. However, velocity is a vector (it has a direction) and, while mass is a scalar (it has no direction), their product would be a vector. Therefore, "momentum" is a vector and, as such, is relevant to the discussion.

What is important is the component vectors. The ball starts with a velocity (momentum) because it is being carried by a player who is running. When it is passed, it is given a new velocity (momentum) in a different direction. It then moves in a third direction which can be determined by drawing a parallelogram of vectors. I can't post diagrams (and there really is no point), so consider the ball's component vectors - one component in the 'forward' direction and one in the 'sidewards' direction. If the passer throws the ball 'backwards', then after the ball leaves his hands, its forward vector component should be reduced (or at least, not increased - in the case of a flat pass). If the forward vector component is increased, it was a forward pass; if not, it wasn't. Simple.

I didn't want to be teacher. I wanted to be a train driver. I just can't help myself.

[Wellsy4HullFC]

and given that velocity is a vector and speed is scalar, that covers direction, too.

Which is why I mentioned velocity being "speed in a given direction".

[Rubber Schnib]

At the risk of starting a row about maths, I should point out that, AFAIK momentum is a fair description.

The statement "momentum = mas * velocity" is true. However, velocity is a vector (it has a direction) and, while mass is a scalar (it has no direction), their product would be a vector. Therefore, "momentum" is a vector and, as such, is relevant to the discussion.

As you noted, mass just multiplies all the components of the vector uniformly - so momentum is a pointless complication to the description unless you're worrying about acceleration due to air resistance and wind effects etc.

I'd stick with velocity - using momentum adds basically nothing to the description, and makes it more confusing for many people who would be happy enough with the idea of velocity alone.

[JohnM]

At the risk of starting a row about maths, I should point out that, AFAIK momentum is a fair description.

The statement "momentum = mas * velocity" is true. However, velocity is a vector (it has a direction) and, while mass is a scalar (it has no direction), their product would be a vector. Therefore, "momentum" is a vector and, as such, is relevant to the discussion.

What is important is the component vectors. The ball starts with a velocity (momentum) because it is being carried by a player who is running. When it is passed, it is given a new velocity (momentum) in a different direction. It then moves in a third direction which can be determined by drawing a parallelogram of vectors. I can't post diagrams (and there really is no point), so consider the ball's component vectors - one component in the 'forward' direction and one in the 'sidewards' direction. If the passer throws the ball 'backwards', then after the ball leaves his hands, its forward vector component should be reduced (or at least, not increased - in the case of a flat pass). If the forward vector component is increased, it was a forward pass; if not, it wasn't. Simple.

I didn't want to be teacher. I wanted to be a train driver. I just can't help myself.

Well, yes you are correct to say that momentum is a vector quantity and taking mass out of it reduces it to essentially a simple velocity problem. I don't see it as an inertia/momentum issue as per the First Law

Incidentally, there is an excellent piece on momentum here I've gone through it and can't fault it.

[JohnM]

Which is why I mentioned velocity being "speed in a given direction".

Just testing!

[terrywebbisgod]

This has quickly turned into an OU lecture.I bet you're all wearing bad 70's clothes

[Wellsy4HullFC]

At the risk of starting a row about maths, I should point out that, AFAIK momentum is a fair description.

The statement "momentum = mas * velocity" is true. However, velocity is a vector (it has a direction) and, while mass is a scalar (it has no direction), their product would be a vector. Therefore, "momentum" is a vector and, as such, is relevant to the discussion.

What is important is the component vectors. The ball starts with a velocity (momentum) because it is being carried by a player who is running. When it is passed, it is given a new velocity (momentum) in a different direction. It then moves in a third direction which can be determined by drawing a parallelogram of vectors. I can't post diagrams (and there really is no point), so consider the ball's component vectors - one component in the 'forward' direction and one in the 'sidewards' direction. If the passer throws the ball 'backwards', then after the ball leaves his hands, its forward vector component should be reduced (or at least, not increased - in the case of a flat pass). If the forward vector component is increased, it was a forward pass; if not, it wasn't. Simple.

I didn't want to be teacher. I wanted to be a train driver. I just can't help myself.

The velocity of the ball in the forwards direction is all that is relevant in measuring a forward pass. If it increases after the pass, it has been propelled forward. If it decreases, it has been passed backwards (as the backwards force has slowed the ball's velocity).

The sidewards velocity is irrelevant in whether the ball slows down or speeds up. It's only relevant to how much it slows down or speeds up, not whether it actually does or doesn't.

The ball doesn't travel forward "due to the player's own momentum". That wording is incorrect, as it implies that a player's mass and velocity affect the pass. A 10 stone player and a 20 stone player running at the same velocity and passing in the same direction will result in the same path. The ball does have momentum obviously (it has a mass and is being propelled at a velocity), but it's not the reason it goes forward. The velocity of the ball in the forwards direction is when being passed is what affects it going forward.

[Wellsy4HullFC]

Just testing!

[Rubber Schnib]

The velocity of the ball in the forwards direction is all that is relevant in measuring a forward pass. If it increases after the pass, it has been propelled forward. If it decreases, it has been passed backwards (as the backwards force has slowed the ball's velocity).

If the velocity increases after the pass in the "forward" direction, there's something funny going on mate!

[Wellsy4HullFC]

This has quickly turned into an OU lecture.I bet you're all wearing bad 70's clothes

I never saw the 70s fortunately

[JohnM]

There is a good explanation here