Description: This demonstration shows that the horizontal motion of a projectile undergoes no acceleration.
Push the cart toward the bridge and the ball will launch up vertically, over the bridge, and back into the cart.
- Howitzer cart
- Ball bearing to match the howitzer
- C-clamp with string and pin attached
- Styrofoam bumper and C-clamp to secure to the table
- Wooden “bridge”
- LONGEST, slate-top table
- Make sure you are using the longest slate-top table you can find (the cart needs a lot of room to make the effect most visible, and the tabletop needs to be as smooth as possible).
- Wipe the table clean of dust and dirt.
- Clamp the string and pin to one end of the table.
- Clamp the bumper firmly to the other end of the table.
- TEST the cart (using the “demonstration procedure” below), to make sure that the ball actually lands back in the barrel.
- Position the bridge so that the ball completely clears it and then lands back in the cart.
- Mark the position of the bridge with chalk or tape.
- Store the cart securely so that it cannot move while wheeling in the table.
- Load the ball-bearing into cart and press it down.
- While holding the ball down, insert the pin into the appropriate hole and feel for it to click into place. You may need to move the ball up and down a little to find the right spot. (NOTE: using the top hole is usually more likely to make the ball land back in the cart, however using the bottom hole makes the effect easier for the class to see, if it is reliably successful).
- Let go of the ball. The pin should now be holding it in place.
- Push cart (NOTE: practice pushing with the appropriate velocity before doing this in front of the whole class. If you push too fast or too slow, the ball will either not make the jump or will miss the cart, or both).