Grade K-3: Try throwing a ping pong ball as fast as you can. Because it is so light, the air slows it down very quickly, so you can’t throw it as fast as a baseball, which weighs more, and isn’t as affected by the air. In baseball, pitchers are able to throw baseballs as fast as 100 mph. That’s 147 feet in one second, or 45 meters per second. Speed travels at about 340 meters per second. In this experiment, when air rushes into the vacuum inside the tube, the only thing it has to push out of the way is the ping pong ball. The exact reason why is slows down so quickly when you throw it is why it can speed up so quickly in the tube, and it comes out the other end of the tube at faster than the speed of sound!
Grade 4-6: As a solid object moves through a liquid or a gas it is slowed by that liquid or gas. It’s for this reason that a piece of paper falls slowly. Normally, a very light weight ping pong ball is slowed down very quickly by the air around it. However, in this experiment the air is instead used to accelerate the ping pong ball. All the air will be removed from the ping pong ball inside the tube, and then reintroduced to just one side. As air rapidly rushes into the vacuum inside the tube, it pushes the ping pong ball towards the opposite end of the tube, accelerating it to several hundred miles per hour. The ping pong ball will exit the tube at speeds faster than the speed of sound and be going fast enough to break through a piece of wood. Immediately after a hole is made in the seal, the ping pong ball has potential energy as a result of the air pushing up against the ball. That potential energy is converted into kinetic energy resulting in the ball being accelerated to high speeds.
Middle School: Normally, the force of air acts against the forward movement of a ping pong ball which is thrown or hit with a paddle will slows it down rather quickly. This limits the speed a ping pong ball can travel at. However, in this experiment, there is no air in front of the ball and as such, when the tube is opened to the atmosphere, there is an unbalanced force acting on the ping pong ball from the air behind it trying to rush into the vacuum that has been created. Since we know that the ping pong ball is very light, the ping pong ball can be accelerated very quickly. It is only in the tube for a small fraction of a second, but in that time the ball is accelerated to over the speed of sound!
College Level: Knowing that the radius of a ping pong ball is 20 mm, the average weight is 2.7 g, and assuming a zero friction system, and a perfect vacuum on one side and atmospheric pressure on the other, (or a pressure differential of 101325 N/m2). Assuming a 5 meter length of the pipe, an initial speed of 0 m/s, use 
, 
, and 
to find the maximum speed the ball could reach by the end of the pipe. Answer: About 686 m/s, or 2.0x the speed of sound! Unfortunately, there are many factors that prevent reaching that speed, the primary of which being that the ping pong ball does not create a perfect seal within the tube, meaning as air rushes in to accelerate the ball, it also rushes in front of the ball reducing the pressure differential, and in turn, the accelerating force. The ball is however, still more than capable of breaking the sound barrier.