Motion in 2 dimensions

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Cart roll demo

Description

Motion in two and three dimensions can be separated into one-dimensional motion in the x,y and z directions. The flight of a skateboarder over a high bar is an example of motion that can be described by one-dimensional motion in the vertical and horizontal directions.

The rolling cart demonstration helps illustrate this point. Shown in the pictures is a side view and a top view of the rolling cart. The cart is pulled at a constant velocity by a string and can roll in a straight line along the horizontal (one-dimensional motion). This uniform motion is shown in the movie.

A ball sits in the cart on top of a spring-loaded plunger. If the plunger is activated, the ball pops up into the air. When the cart is stationary, this motion is also one-dimensional (vertical) as seen in the movie. Note that the ball leaves the frame and re-enters during this movie. This is to emphasize the vertical motion of the ball.

The two motions can be put together to create a two-dimensional motion of the ball as shown in the movie. As the ball moves up and down in the air, it is also moving horizontally (at constant velocity) with the cart, so it lands back in the cart.

1. Draw the motion of the ball in the reference frame of the cart.
2. Draw the motion of the ball in the reference frame of the table top on which the cart rolls.
3. Would the ball land in the cart if the cart is accelerating? Explain your answer.