# Rocket thrust

1. Oct 4, 2009

### wolfspirit

This is my first posting - I don't know whether its on the right section but I have a question
is there a formular to work out
how much thrust you need to get a certain weight of rocket up in the air, also for the rockets altitude?
Thanks

2. Oct 4, 2009

### Staff: Mentor

Newton's laws of motion. Start with f=ma, s=at and d=st. How complex of a scenario are you trying to analyze?

3. Oct 5, 2009

### wolfspirit

Thank you. As for how complex - not very. I'm just thinking about making a model rocket and i wanted to work out how much thrust i will need to get it to a designated altitude.
Can you please just confirm what the letters mean. (f=ma, s=at and d=st) Am I right in thinking they are f=force, m=mass, a = altitude, s=speed, t=time d=distance?
Thanks again!

4. Oct 5, 2009

### Molydood

'a' is acceleration not altitude :-)

5. Oct 5, 2009

### LURCH

Unfortunately, these calculations can get quite compluicated, as the "m" keeps changing. As your rocket burns fuel, it becomes lighter, yet the thrust "f" remains the same. So, same thrust with less mass means greater acceleration.

I think (and I hope someone will correct me if I'm wrong here) you can get a fairly good approximation if you figure in only half the weight of the fuel. Since the rocket starts off lifting all pof the fuel and ends up with none, half would be the mean average of the fuel mass.

Also, if you go on NASA's website (NASA.Gov), you can find some pretty cool tutorials.

6. Oct 5, 2009

### wolfspirit

Thanks for that yes I can see how complicated it can get. I'll check out NASA'S website.

7. Oct 5, 2009