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?
Cart was pushed, it was given an initial Velocity and, since there was
friction on the cart, it stayed at that constant Velocity. The plastic
attached to the cart when it was given the Initial Velocity, so the
given the same Constant Velocity. For this experiment we are going to
air resistance was negligible. So according to Newton’s I First Law of
Objects in motion will remain at the same state of motion unless acted
an external force. Since the Ball and the cart are going at the
and there are no forces affecting the Horizontal Velocity of either the
the ball, The constant velocity should have no effect on the Horizontal
in distance between the Rubber ball and the cart. In the photo at the
right you can
happens if we subtract this Velocity from both the cart and the ball.
seems to go straight up and straight down. The Fact that the Ball goes
down has do with the Gravitational Forces acting on the ball, which
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.