AMath: dismal as usual... 10m question at the back zzz.
Tried to do a trick:
1st Attempt: tried to kick a 500 ml PET bottle through the doorway. Unfortunately, it sailed wide left, and ended up near the dustbin. I thought about it and brought in soccer free-kick techniques.
2nd Attempt: This time, it was brilliant !!! The PET bottle glided past the doorway, dead centre and hit the corridor (wall). The projectile had a nice trajectory, sort of a parabolic trajectory (like a knuckle shot if you can imagine it) I think I did that about 6 meters away from the doorway. Thankfully it did not overshoot the corridor, if not that would be considered high rise littering.
* 500ml Polyethylene terephthalate (PET) bottle courtesy of Daniel Lam.
Here comes the astonishing part. As I was just about to retrieve the PET bottle, I saw Mr Wee. I think Mr Wee was just beside the doorway when the projectile struck the wall. If that ‘free-kick’ had occurred even a second later the consequence could have been worse.
Indeed, the trajectory of a bottle is very difficult to predict, unlike regular objects like a sphere. I’ve managed to demonstrate the Magnus effect previously, using a soccer ball.
Magnus Force:
F = lift force
ρ = density of the fluid
r = radius of the ball
v = velocity of the ball
A = cross-sectional area of ball
CL = lift coefficient
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