Re: Golf Ball Trajectory Question

[Chuck Britton <britton@NCSSM.EDU>]

At 2:22 PM -0400 7/15/03,  Frank Cardulla wrote:

>  one site stated that the speed of a struck=
>  ball could never=20
> be greater than the speed of the clubhead.


Conservation of Linear Momentum is useful here.
If the ratio of clubhead mass to ball mass is large - then the ball
cannot travel faster than TWICE the speed of the club head.

       For every totally elastic collision -
       the speed at which the two objects approach each other
       is equal to the speed at which they separate.

Relative speeds should already be covered in class.

This little tidbit should be a part of every intro physics course.
Proof is done in the C.M. system and needs Conservation of KE also.
I use the relationship (with proof promised later) well before we
even do acceleration (except of course for finding the area under a
velocity time graph that has a constant slope - we'll NAME that
constant slope LATER!!!!)


> My intuition told me that with an initial speed of 127 mph, a golf ball
> struck in a vacuum should travel farther, because of the lack of air
> resistance.

Your intuition hasn't noticed yet that the ball's trajectory actually
curves UPWARD as the ball comes off the tee. There is an appreciably
upward force caused by the rapid spin of the (dimpled) ball
interacting with the air itself.
This force is usually called 'lift' but other more complex names are
often used.

Take away the AIR - you do loose it's drag force - but you also loose
this substantial lifting force which exists as long as the ball is
spinning. Dimples were 'invented' to increase this interaction
between the ball and the air.
--
I never teach my pupils; I only attempt  to provide the conditions in
which they can learn.
 - Albert Einstein