Video demonstration experiments show the laws and concepts in action.
The Howitzer (Projectile) cart is an excellent example of two dimensional motion. With our set up, a ball is placed in a projectile launcher that can be set off by a trigger on the iPad. In our first experiment, we set the cart in motion with a constant horizontal velocity. Next, the trigger is pressed and the ball is launched into the air where it experiences vertical acceleration due to gravity whereas its horizontal velocity is unchanged. Because the ball’s horizontal velocity remains the same as the cart’s, both the ball and cart cover the same horizontal distance, resulting in the ball landing back into the cart’s bucket. This demonstrates that horizontal and vertical motion are independent from each other.
In our second experiment, the Howitzer cart is put on an incline. Once we let the cart go, it will experience constant acceleration due to gravity. The trigger is then pressed, launching the ball into the air, but the ball still lands back in the bucket. This is because the ball and the cart experience the same acceleration due to gravity in projection onto the cart’s path.
For our third experiment, the Howitzer cart is attached to a pulley-mass system. Once we let the cart go, it will be pulled by the weight of the hanging mass. The ball is then launched into the air, but while airborne, the ball moves with constant velocity in the horizontal direction whereas the cart moves with a nonzero horizontal acceleration. This results in the ball missing the bucket.
This demonstration is used to study projectile motion. In this experiment, we want to confirm that the range of an object launched at 30° is the same as for the object launched at 60°, and that 45° will give us the largest range. It is also important to note that, even though objects launched at 30° and 60° cover the same range, the time they took to do so was different.
Imagine that a hunter spots a monkey hanging off a tree branch. The hunter points their tranquilizer gun directly at the monkey and shoots. The monkey reflexively lets go of the branch immediately after the hunter presses the trigger. After the bullet leaves the barrel, the only thing acting on it is the same force acting on the monkey, and that is gravity. The bullet and monkey will fall at the same rate, thus guaranteeing that they collide. This demonstration is a good example of projectile motion.