Rocket Launch Lab: Why Rockets Are Mostly Fuel
Apply Newton’s third law and conservation of momentum to a rocket: thrust equals mass flow times exhaust speed, the rocket lightens as it burns, and dropping empty stages lets the rest go faster.
Before you try
What if you could not drop the empty first stage? How much more fuel would you need?
Try it out
Interactive activity
Sign in to play
Use a Google account (yours or a parent’s) to unlock this simulator. We store only your name and email so your favourites and progress follow you.
Signing in needs an internet connection. Once you are signed in, simulators also work offline.
Free preview
Loading controls…
What happened?
Move a control to see what changes and why.
Straight-up flight with simple air drag; a real launch tips over to build sideways speed and engines work better in vacuum.
Something went wrong
This simulator could not load. Check your connection and try again.
Try these ideas
- Launch the default rocket with staging on, then off, and compare the final speed.
- Raise the payload until the rocket cannot lift off. What is thrust ÷ weight then?
- Switch to a hydrogen engine (exhaust 4,400 m/s). How much less propellant do you need?
Why it works
A rocket moves by throwing hot gas out of the back at very high speed; the gas pushes the rocket forward (Newton’s third law). Thrust equals the mass thrown out each second times the speed it leaves at. To lift off, thrust must beat the rocket’s weight, and since most of that weight is propellant, the rocket gets lighter and accelerates harder as it climbs.
Reaching orbit needs about 7.8 km/s, and the rocket equation says the speed gained depends on the ratio of full mass to empty mass. That is why launchers are 85 to 90% propellant, and why they drop empty stages part-way up: dead weight no longer has to be carried. In this lab you set the payload, propellant, exhaust speed, mass flow and staging, then launch and read the speed at engine cut-off.
Check your understanding
Question 1 of 4
A rocket’s thrust comes from
Thrust ÷ weight is 0.9 at lift-off. The rocket
Why does staging help?
Most of a launch rocket’s mass is
Explain it in your own words
What changed? Why did it happen? Where might you notice this in everyday life?
For parents & teachers
- Let go of an inflated balloon and discuss which way it moves and why.
- Ask: why does ISRO’s PSLV have four stages?
- Estimate how many kilograms of fuel a 1 kg satellite needs to reach orbit.