If the ‘forward pass’ rule did not stand as it does today 50% of all passes would be forward. Momentum of the ball has and always will be taken into account.

Having said that FDP pass to Habana on Sat was right on the very edge….could have gone either way if a touch judge was in line to see it.

sheesh..

who said rugby players were dumb…?

think of all those calculations they have to make just to pass the ball…!!!

yeah…

but it wasn’t boring when you took my sucker punch hey?

86. charo :
November 3rd, 2009 at 12:05 pm
#84 Tacitus:

aw gee – you beat me to it

The Forward Pass

If a ball is thrown diagonally backwards by a stationary player, the ball has actually got two speeds, one directly backwards, and one towards the touch-line. This means it travels across the field of play (from touch-line to touch-line) at a speed U and backwards (away from the opponents dead ball line) at a speed V. Put another way, a spectator standing on the touch-line would see the ball travelling backwards at V, whilst a spectator standing behind the uprights would see the ball traveling across the field at U.

Consider a player, P, running at speed S towards the opponents’ goal-line with the ball. The instant he passes the ball, it also has speed S forwards

Now consider two players, A and B, with B 1m behind and 6m across the field from A. Assume also that they are facing the opponents’ dead-ball line. If they are both standing still, and A passes the ball to B in 1 sec, then its speed backwards is 1 m/s and 6 m/s across the field of play.

Now assume that both players are walking forward at 1 m/s, and A again passes the ball to B in 1 sec. As the ball leaves A’s hands, it has a speed of 1 m/s backwards, as before, but because A is moving forward at 1 m/s the ball also has this speed. This means the ball has zero speed in the forward direction and it actually travels directly across the field of play and does not go forward. However players A and B and the referee (a good one who keeps up with play!) are all moving at 1 m/s, so to the referee the ball is passed backwards as before, but the spectator sees the ball moving directly across the field of play.

Let’s now assume that the players and the referee are moving forward at 3 m/s, and the ball is again passed from A to B in 1 sec. As the ball leaves A’s hands it has a forward speed of 2 m/s (3 – 1) m/s. The referee sees the ball passing backwards from A to B, as before, because he is moving with the players. But the spectator cries foul: he sees the ball moving forwards across the field of play at 2 m/s!

For the spectator to see a pass which he judges not to be travelling forward, the ball must at least have a backward component of 3 m/s (the ball would then travel directly across the field of play). This means it covers the back distance of 1 m between A and B in 1/3 sec. In turn this means the ball reaches B, covers the 6 m across the field in 1/3 sec and so the speed across the field is now 18 m/s (6 divided by 1/3). Passing a ball at this speed whilst running at 3m/s (11 km/h) is not easy! And 11 km/h is not fast.

Normally a wing, or other back, running at a fair speed, say 5 m/s (18 km/h or running 100m dash in 20 secs) would need to pass the ball to B at over 130 km/h for the pass not to travel forward. The ball would need a backward component of 6 m/s, and so the back time would be 1/6th sec and the speed across would be 36 m/s. Of course if B were to move further back, then the passing speed would decrease, but then it would have to be increased if B moved away (across) from A. A really fast back, probably running at say 8 – 9 m/s (or a 100 m dash in 11 – 12 sec) would have to pass the ball to his team-mate at nearly 220 km/h for the pass not to travel forward.

These things become particularly clear to spectators when the ball is passed between running players as they cross the 10 m, centre or 22 m line. It is fair to say that virtually all passes between running players will travel forward since the balls travels towards the opponents dead ball-line during the pass. This is what is seen by stationary observers, spectators, but not be the referee who is running with the players.

#92 gunther: The sheer girth of the bloated obese Bulls supporter would counter that.

yeah, boring subject anyway

#89 katman:

“That “flat” ball is travelling forward as fast as the guy who passed it was running.”

so that’s not quite true…

Just nitpicking bud…

quite right… bad choice of words… wasn’t actually meaning physics itself was strange but that our perception of it can be…

yeah yeah… read above… but we don’t play rugby in a vacuum…

Would be fun to see this. How do I get hold of Mythbusters?

sure they will… but we don’t play rugby in a vacuum… even if some players appear to be quite vacuous between the ears…

my point is that the density of a rugby ball is much lower too… the speed of skydiving amplifies the disparity in speeds… or another way… because the rugby player doesn’t run as fast as a diver can fall it appears the ball leaving his hands is moving at the same speed as the player but atmospheric friction means it slows down immediately it leaves his hands and continues to do so until caught or being overcome by gravity…

aw gee – you beat me to it

air resistance.
if it was done in a vacuum, both would carry on at the same speed.
remember a physics lesson at school eons ago.
a feather and a solid object dropped in a vacuum both hit the bottom together.

Nothing strange about that.

The basketball’s density is much lower, and therefore the air resistance affects it to a much greater extent than it does the plummeting skydiver.

Do that experiment in a vacuum, and the two will drop at exactly the same speed.