• A rocket converts potential energy of a pressurized gas  into a kinetic energy .
• The rockets exhaust gas molecules exits the rocket’s nozzle very fast, giving them a lot of momentum.
• The ejected jet exchanges its momentum with the rocket and the rocket then moves in the opposite direction of the exhaust with the same total force.

What makes a water bottle fly?

1.  The compressed air pushes on the water as it tries to expand.
2.  The water pushes downwards through the nozzle.
3.  The water rushes through the nozzle, making a thrust to counter the weight and air resistance.
4.  The thrust pushes the rocket upwards into the sky.
5.  The fin and the nose cone keep the rocket from tumbling.

Rocket thrust equation

Thrust (F) = Mass flow rate (ṁ)  x  Velocity (V)  +  (Pressure (Pe)  –  Pressure (Po))  x  Area (A)

Rocket thrust is calculated by multiplying the mass flow rate by the velocity and adding the difference in pressures multiplied by the area.

What happens if there is too much water in the rocket?

1. The rocket runs out of air pressure before all the water is pushed out
2. Since the water is no longer being pushed out the rocket loses thrust
3. The rocket and all the extra water fall to the ground

What happens if there is too little water in the rocket?

1. The rocket runs out of water before it runs out of air pressure
2. Since there is no more water rushing through the nozzle, the rocket loses thrust
3. All the extra air pressure is wasted
4. The empty bottle coasts for a while before falling