Physics Demo Number: 172

Approximate

Run Time: 5 min

Shepard's Crook Pink Ball Release and Catch by Ballistic Cart

Demo Description

As a cart travels past a trip bracket, an electrical pulse neutralizes the magnetic hold on a ball at the top of a rod attached to the cart.

This sequence of events allows the ball to undergo free fall vertically as it continues its shared horizontal motion of the cart.

The ball thus falls vertically into a receptor straight below it, as seen from the frame of reference of the cart.

From the lecture table frame of reference, the ball follows a parabolic path as it descends into the cup.

 

Scientific Principles

  • The horizontal and vertical components of the motion of a projectile in the gravitational field of the earth are mutually independent of each other.

Equipment

  • Pasco Track

  • Cart

  • Ballistic Cart Accessory (which also doubles as drop rod accessory)

  • Trigger Post

  • Drop Rod

 

Equipment Location

  • Track lives on a wall bracket on left rear wall of prep room (opposite the [H] Columns).

  • Kit (115) on [H-4-5] contains the Cart, Ballistic Cart Accessory, and Trigger Post.

  • Two drop rods hang vertically from top of [H-4-x] and [H-5-x] columns.

Instructions



The first photo shows the “Shepard's Crook” or “ Drop Rod” attached to the ballistics cart accessory on the Pasco Track.

The second photo


gives a closer view of the cart from the front.

The third photo


gives a look at the cart from the right end, showing that the rod's electrical plug has a mating Jack on the side of the ballistic cart accessory.

The net result of all this hookup is that when the power switch above the drop rod jack is “ on” and the cart travels past the photogate trip bracket, an electrical pulse neutralizes the magnetic hold on the pink ball at the top of the drop rod , allowing the ball to free fall vertically as it continues its shared horizontal motion of the cart.

The ball thus lands in the cart after:

     1)  following a parabolic path in the lab frame, but 

     2)  falling vertically in the cart's frame.



Writeup created by David A. Burba.
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