When you pump your bicycle air pump fifty times, the work that you do is being stored inside the pop bottle as compressed air.

Air is very springy and when it gets a chance, it bounces back to its original volume. The only way it can do that is to come rushing out the nozzle at the bottom of the rocket.

You feel tired after doing fifty pumps because you have delivered some of your energy to the rocket. But the rocket now contains the energy that you have lost, in the form of compressed air.

A lot of people make the mistake of thinking the rocket pushes on something (for instance, the ground). This is not true.

The rocket moves forward by throwing its exhaust (the air and water) out the nozzle as fast as possible.

It does not push on anything, like the ground or atmosphere. Example: if you were sitting in a small boat full of baseballs and one-by-one threw the baseballs out the back of the boat, the boat would move forward on the water.

The faster you threw the baseballs out the back of the boat, the more force would be applied to moving the boat forward.

This is not a very good way of moving your boat around.

And indeed, it is a very inefficient way of moving a rocket around, but what else can you do? There’s nothing to push on in outer space.

Antigravity water rockets work much the same way that a bullet does. Each stage of the rocket (and indeed the entire rocket!) is inherently unstable and tail-heavy. Stability and straight-up flight are achieved by spinning the rocket. When a rocket stage is out of pressure and has reached as high as it can go, the spinning slows down or stops and the tail of the rocket starts to fall first. However the tail has more air friction than the front and the falling rocket soon settles in to a gentle sideways descent.

Space tip: Outer space rockets don’t have any fins because there is no air out there to push the fins back. They use gyro-sensors to automatically aim the nozzle in different directions to keep the rocket pointed straight.

In the first fraction of a second when a rocket is lifting off of the ground, it is not going fast enough for the fins to keep it pointed straight up. And the angled fins are not moving fast enough through the air to spin the rocket. To solve this, on the base of the launcher there are three curved guide rods that engage 3 loops on the Stage 1 ring fin structure. During liftoff, the rocket moves up and is automatically spun by the three curved rods. When the rocket leaves the curved rods it is spinning fast enough for the rocket to be very stable and go straight up.

It may be helpful to look at the launcher hose connector while reading this so that you can more easily visualize how it works.  The specialized connector at the rocket end of the filling hose has a rubber O-ring that seals on the inside of the bottle mouth, and two angled teeth that engage a circular groove under the centre of the ring fin. When you pump up the rocket with air, the pressure inside the connector’s air passageway fills a rubber tube that presses out on these teeth, keeping them engaged in that groove.

When the pressure reaches about 80 psi, it pushes on the pressure relief valve and starts to open it. The escaping air keeps the pressure from ever going higher than 82 PSI, and it exits through a whistle that lets you know that it’s time to launch.

When you disconnect the filling hose from your air pump, several things happen:

• First, a one-way air valve closes to prevent the high pressure air in the bottle from coming back into the connector.
• Then the high pressure air in the connector all leaks out, back through the filling hose.
• Now the rubber tube is empty and stops pressing on the engaged teeth, which slide off of the angled inside of the groove that they were in because the air in the bottle (at about 82 PSI) pushes the connector out with a force of about 46 pounds (about 21 kg).
• That same force pushes the entire connector out of the mouth of the bottle and your rocket launches.

It’s important to know that you don’t have to wait for the whistle to sound before launching. You can launch at a much lower pressure, as low as 30 psi in the rocket. But it’s also important to know that the pressure in the rocket is almost always much lower than the reading on your pump, because of the long, thin filling hose that limits how fast the air can get through. This is an important feature, because it allows the overpressure valve to keep up with the incoming air. Even if the pump or compressor is running at 120 to 150 PSI, the overpressure valve will be able to dump all the unwanted extra air through the whistle to keep the bottles from getting too near to burst pressure.

There! Now, did you imagine that there was so much going on inside that filling hose?