High School Rocket Project

1. Mar 7, 2013

alchemistf9

I am a high school teacher attempting to give my students a project for designing a rocket powered by the chemical reaction between acetic acid and baking soda to produce CO2 gas.

I have done some simple calculations based on stoichiometric amounts of vinegar and acetic to produce a stoichiometric amount of CO2. I then have taken the moles of gas produced and solved for the pressure produced using the ideal gas law equation.

The calculations are attached in the Excel file.

Now I come to the troubling part. The students will be using a 2-L soda bottle as their rocket.

As the physics part of the project I would like to the students to calculate many things:

Fthrust and work done by the gas.

What are the simplest equations to use to calculate Fthrust and Work ?

I've attempted to make several equations which give me some very non-sensible results.

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2. Mar 8, 2013

Staff: Mentor

Do you plan to use some reaction mass, like water? A direct CO2 exhaust is quite inefficient. There are several threads about rockets in the forums (at least one of them is in the "Similar Threads" list below).

3. Mar 8, 2013

PhysicoRaj

I think the products, sodium acetate and water, or simply sodium acetate solution can act as the reaction mass right?

4. Mar 8, 2013

Staff: Mentor

I'm not sure if that is a good idea...

5. Mar 8, 2013

alchemistf9

The reaction mass is the whole thing yes.

6. Mar 8, 2013

alchemistf9

I just need a simple equation for the force of Thrust

7. Mar 8, 2013

Staff: Mentor

$F=\frac{dm}{dt}v \approx \rho A v^2$ where A is the area of the nozzle, rho is the density and v is the velocity there. Neglecting compression and inefficiencies, $\rho v^2 = 2 \Delta p$ with the pressure difference inside/outside. For gas as reaction mass (bad), compression is relevant, of course, so it might need a better analysis.