On
Wednesday October 4th, the Physics
Class at Warren Wilson College conducted the following experiment: A
person (Eric Thiedich) was sitting on a
wheeled
platform and was given a push. Then while the cart was moving, Eric
launched a small plastic ball into the air with a mechanical
"popper-upper"
device. To the surprise of much of the class when the ball
was
launched, it traveled the same speed as the cart and went
back to the
same relative place that it was launched from. Why didn’t the ball land
behind
the cart?
When the
Cart was pushed, it was given an initial Velocity and, since there was
little
friction on the cart, it stayed at that constant Velocity. The plastic
ball was
attached to the cart when it was given the Initial Velocity, so the
plastic
ball was
given the same Constant Velocity. For this experiment we are going to
say that
air resistance was negligible. So according to Newton’s I First Law of
Motion,
Objects in motion will remain at the same state of motion unless acted
upon by
an external force. Since the Ball and the cart are going at the
same
velocity,
and there are no forces affecting the Horizontal Velocity of either the
Cart or
the ball, The constant velocity should have no effect on the 
Horizontal
change
in distance between the Rubber ball and the cart. In the photo at the
right you can
see what
happens if we subtract this Velocity from both the cart and the ball.
The Ball
seems to go straight up and straight down. The Fact that the Ball goes
up and
down has do with the Gravitational Forces acting on the ball, which
gives the
ball a vertical acceleration of -9.8m/s2.
In
the last photo (left) both the ball and the cart are plotted with
circles and vertical lines respectively. You can see that the Cart and
the Ball stay at the same
Horizontal
Velocity. This Velocity is independent of the Gravitational Force which
causes
the ball to have a negative vertical acceleration.
All animated photos were processed by Donald Collins with DV
tape photographed by students.
