My PBL Project

1. Introduction

A car rolling across a table fires a projectile straight upward and subsequently catches it, illustrating that the horizontal velocity of an object is independent of the vertical force.

Driving Question: What kind of motion can be observed in the horizontal and vertical motion of a projectile?

2. Materials

My Materials

3. Procedures

Step 1:

Put one of the metal balls into the barrel of the ballistic car.

4. Scientific Principles

This demonstration illustrates the independence of the vertical and horizontal motion of projectiles. Since the ball is launched from a car moving with a constant horizontal velocity, the ball has the same horizontal velocity as the car and thus remains directly above it (ignoring friction of the wheels and the possibly different air resistance of the ball and the car). Alternately, one can use this demonstration to illustrate the transformation of coordinate systems. In the inertial system moving with the car, the ball moves straight up and down. In the system fixed in the room, the ball follows a parabolic trajectory.

5. Safety Regulations

  • Make sure that the ground is flat and level when you push your ballistic car.

    • If the ground is bumpy or inclined, the ball will most likely not fall back into the barrel.

  • DO NOT keep your face on top of the barrel when it is loaded. POTENTIAL EYE DAMAGE!

    • The trigger might go off, and the metal ball may hit you in the face.

Step 2:

Push the ball down the barrel until you hear a click.

The Ballistic Car

Step 3:

Attach the string to the trigger by sticking the magnet onto the metal part of the trigger.

String with an Attached Magnet at the End

Step 4:

Hold the string out at an angle from the ballistic car.

Metal Balls of Differing Weights

Step 5:

While holding the string in one hand, give the ballistic car a slight push with the other hand.

NOTE: Make sure that the ballistic car is on LEVEL GROUND.

Step 6:

As the ballistic car is accelerating away from you, tug on the string so that the magnet detaches and the trigger goes off.

Step 7:

Watch as the metal ball is shot from the barrel into the air and lands back.