Pasco Scientific ME-9486, Instruction Manual And Experiment Manual

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Ballistic Cart Accessory 012-05460A
Teacher’s Guide
Experiments 4 and 7: Inclined Plane - Demonstration
Why the Ball is Still Caught in the Inclined
Plane Experiments
There have been enough questions about these two
experiments—including some from people who
should know better—that we thought it would be
best to explain exactly what was going on and why
the ball is still caught.
First, let’s consider the horizontal case:
The cart and the ball have the same horizontal
component of velocity. The vertical component of
the ball’s velocity does not affect the alignment of
the ball and cart, so the ball lands in the cart.
The horizontal component of the acceleration of
both cart and ball is the same: zero, which ensures
that the ball and cart remain aligned.
Now let’s consider the case where the cart is
accelerating:
Velocity Acceleration
Acceleration
In this case, the ball’s acceleration is still only in
the vertical plane, but the cart has a horizontal
acceleration. This horizontal acceleration changes
the velocity of the cart, but not the velocity of the
ball. The cart does not remain directly beneath the
ball and the ball is not caught.
When the track is tilted, things become a bit more
complicated; but if you break the vectors into their
components it becomes more clear:
The cart and the ball have the same component of
acceleration parallel to the track. Since they have
the same initial parallel-component velocity and the
same acceleration, they will thus always have the
same parallel-component velocity. The ball will
always be on a line with the cart perpendicular to
the track, and it will be caught.