Rocket Simulation

The simulation flies a 200 kg rocket straight up. Set its thrust, and the free-body diagram, the net force, the acceleration and the velocity all change with it.

Clock reading: t = 0.0 s
Height: y = 0 m

A dot marks its height at each second.

Clock speed

Step 1 of 4: Launch

The rocket sits on the pad. Its weight is 2000 N. Launch it with a thrust of 3000 N, one and a half times its weight, and watch the free-body diagram: the thrust arrow is longer than the gravity arrow.

Thrust0 Nits weight is 2000 N

Free-body diagram

every force on the rocket

m = 200 kg

Net force

the forces added

F_net = 0 N

Acceleration

a = F_net ÷ m

a_y = 0.0 m/s²

Velocity

changes by a each second

v_y = 0.0 m/s

At rest on the pad.

The second law, for the rocket right now

F_g, the pull of the earth on the rocket, is mg = 2000 N: a magnitude, always positive. Gravity points down, along −y, so it goes in as −2000 N, with the minus sign put in by hand.

On the pad its velocity stays zero, so a = 0, and the pad pushes up with the weight minus the thrust.

Keys

The keys work while the simulation is selected: click anywhere on it first.

0 to 6: The thrust presets, from off to 4000 N
↑ ↓: 100 N more or less thrust
Space: Engine off
L: Landing legs out or folded
T: Change the speed of the clock
P: Pause or play
R: Reset

Start with the guided run. It flies the rocket in four steps: a thrust bigger than its weight, then exactly its weight, then half of it, then none. Before each step, decide what the velocity will do. Then fly it yourself in the free play, on other planets too, and try the landing challenge.

As the rocket flies, look for the following:

When the thrust equals the weight, the net force and the acceleration are both zero, and the velocity holds at whatever it was. The dots are evenly spaced.
When the thrust is less than the weight, the net force points down, even while the rocket is still rising. The velocity shrinks, and the dots bunch together.
The acceleration arrow always points the same way as the net force arrow. That is the second law, $\vec{a} = \vec{F}_{\text{net}}/m$ .