how fast will it go, page 3

how fast can it go?
page 3

i would like to give you an opportunity to try filling in some numbers so that you can compare what changing momenta will do in one-dimensional elasatic collisions, but i couldn't find a java applet that demonstrated what i wanted. i guess i'll just have to wait until i can program in java.

i'm going to need to wait a while to do this derivation. for one thing, it doesn't come out properly the way i'm currently approaching it. i'm not sure whether i need to introduce forces, or if i'm just not setting it up right. i'm also rusty as Fe₂O₃. however, the wonderful thing about the Web, being at the fairly mature stage it is, is that you can usually find what you need if you look around. the media lab at MIT has this derivation and a whole lot more. so i guess i can go brush up on things. also, their derivation includes the effect of gravity, which mine below does not. note the differences.

in the meantime, i guess i'll just give you the result. i'll put a form below, also, so you can try a few computations yourself. remember: this formula assumes there are no outside forces -- no gravity, no wind resistance, nothing. this formula will work for a rocket in space far from any stars, planets, etc. to act on it with gravity. again, see the MIT derivation if you want the full picture.

v = u ln(m₀/m)

in the above equation:

v is the rocket's final velocity, i.e. how fast it will go

u is the velocity of the propellant leaving the rocket

m₀ is the inital mass of the rocket + fuel + payload (the mass at the start)

m is the final mass, after fuel has been spent, stages have been dumped, etc.

let's try entering some values below and getting a few results! one thing I will insist on is that you use the metric system. don't get confused like those poor mars mission engineers a couple years ago -- stick with metric! if you're feeling metric impaired, i've included a couple of buttons for converting things. i'd like to stick with kilograms (kg) for mass and meters per second (m/s) for speed. you'll probably try entering them as pounds and miles per hour, so the first buttons will help you convert those. below that is the area for entering the variables for your rocket, as well as the result. below that are buttons you can press to get some default answers if you don't have numbers to input. i tried to include some classic rocket examples here.

note the values that appear above when you click the following buttons:

the largest rocket ever flown, the , the rocket that took us to the moon and back. previous page ducks and rockets