Rocket Launch
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flagWhat you'll discover
- arrow_forwardUse Newton’s third law to explain how rockets push
- arrow_forwardBalance thrust against weight to lift off
- arrow_forwardSee why a rocket accelerates harder as fuel burns away
- arrow_forwardUnderstand escape velocity (~11.2 km/s) as an energy idea
Rockets push on their own exhaust
A rocket does not push against the air or the ground. It throws hot gas downward at enormous speed, and by Newton’s third law — every action has an equal and opposite reaction — the gas pushes the rocket up just as hard.
That is why rockets work perfectly in empty space where there is nothing else to push on. The "thrust" you set in the simulation is exactly this reaction force, measured in kilonewtons.
The tug of war: thrust vs weight
At the launch pad, two forces fight: thrust pushing up and weight (mass × gravity) pulling down. If thrust is smaller than weight, the rocket just sits there burning fuel — try it!
The net acceleration is (thrust − weight) ÷ mass. Engineers call thrust ÷ weight the thrust-to-weight ratio, and it must be greater than 1 to lift off. Real launchers leave the pad with a ratio of only about 1.2 to 1.5 — a surprisingly gentle start.
Lighter every second
Here is the beautiful trick: as the engine burns, the rocket throws its own mass away. A lighter rocket with the same thrust accelerates harder, so rockets speed up faster and faster — watch your velocity graph curve upward.
This is also why rockets use stages. When a fuel tank empties, it is dead weight, so the rocket drops it. Shedding the empty first stage lets the remaining engine push a much lighter ship. Look for the stage falling away in the simulation.
The edge of space and escape velocity
Space officially begins at the Kármán line, 100 km up — that is your target altitude. But reaching space and staying there are different: to orbit you must also gain about 7.8 km/s of sideways speed.
To leave Earth completely and never fall back, you need escape velocity: about 11.2 km/s, more than 30 times the speed of sound. It is not a speed you must have at launch — it measures the total energy needed to climb out of Earth’s gravity well.