Anthony said, "The shot gets through, then appears to deflect behind the
goalie..."
The way I see it, that's not what happened. First of all, the shot did not
get through. It hit the goalies' hockey stick. The puck came in very high.
It actually passed over the top of his right leg, hit the bottom of the
hockey stick, and deflected downward (toward the ice) as well as *straight
to the right* (as viewed from the front of the goal). The reason it looks
like it deflected sideways (behind the goalie) is because of parallax. The
overhead camera is not directly overhead; rather, it is behind the goal
line. You can be certain of the overhead camera position because we see the
crossbar of the goal positioned left of the goal line as seen on the ice.
Therefore, a puck falling straight down (toward the ice) will appear to be
moving toward the goal line. That is, in the overhead view, higher objects
appear left of the goal line (just like the top crossbar), and they will
appear to be moving toward the goal as they fall.
So the puck is heading toward the goal and is airborne. It appears to me
its height (when it gets to the goalie) is a bit over halfway from the ice
to the cross bar. The cross bar is 4 feet above the ice, so I would say the
puck is coming in at roughly 2'4" above the ice. The puck passes over the
goalie's right leg somewhere over the thigh (as opposed to over the knee or
shin). The puck hits the stick, and then we get our first good view of the
puck while it is headed downward toward the ice, as well as pretty much
straight toward the right; that is, moving downward and also pretty much
parallel to the goal line. From the overhead view it only appears to be
moving toward the goal because of parallax. As soon the puck hits the ice,
it does bounce a bit, but not very high, so parallax is not much of an issue
anymore, so we see the puck continue to the right on the same path it always
had (after hitting the stick).
The transition from falling to not following is sudden, so the transition
from a parallax problem to no parallax problem is also sudden, and that
gives us the appearance of a sudden change in horizontal direction, but at
that point it's only a change in vertical motion. The change in horizontal
direction occurred at the stick.
Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Chair, Division of Natural and Applied Sciences
Bluffton University
1 University Drive
Bluffton, OH 45817
419.358.3270 (office)
edmiston@bluffton.edu
-----Original Message-----
From: Anthony Lapinski
Sent: Saturday, November 19, 2011 10:51 PM
To: phys-l@carnot.physics.buffalo.edu
Subject: [Phys-l] Cool hockey save! What happened?
One of my students, a hockey player, sent me this short clip. The shot
gets through, then appears to deflect behind the goalie -- probably from a
hole/divot in the ice. Watch it from all angles in slow motion. Amazing!
Might be good for students to analyze.