parachuting

Yesterday I visited the dentist and he was nice enough to let be choose a toy from the treasure chest. As searched through the box I saw sticky hands and bouncy balls and my first thought was, "wow, this box is filled with physics!" I chose the parachuting army man. When i got home I was throwing it up in the air. When it first begins to drop, the parachute is not fully opened and the army man falls quickly. When the parachute finally opens up, the man begins to fall much slower. I wonder what made this difference and realized it was air resistance. When i release the army man in the air there are two forces acting upon it, gravity and air resistance. A free-falling object on Earth has an acceleration of -9.8 m/s^2 due to gravity. However, this number ignores air resistance. When the man is in the air without the parachute opened, air resistance is only acting upon his body. The parachute increases surface area and causes an extra upward force, so that the army man will begin to accelerate in the upward direction or decelerate. This allows for the army man to make a safe landing unscathed.

ping pong

Today I was playing ping pong at my friend's house and realized that many aspects of physics were in the game. When I serve the ping pong ball, my paddle makes contact with the ball causing the ball's acceleration to increase. Velocity also increases as the ball, whose initial velocity was zero, flies over the net. As the ball reaches my friend, the rate at which the ball is accelerating decreases, and velocity decreases.

When my friend returns the ball, his paddle exerts a force upon the ball causing it to change direction and come back towards me. Because the direction and speed of the ball changes, velocity changes as well and becomes negative.

Playing ping pong also shows displacement which is the direction and distance of the shortest path between an initial and final position. Before I serve the ball, displacement is zero because it has not traveled any distance. The ping pong table is nine feet in length. As I serve the ball over the net, displacement changes. Once the ball reaches my opponent, displacement becomes +9.0 feet. As the ball returns back to me, displacement becomes negative. When the ping pong ball reaches its original starting position, displacement returns back to zero.