This graph says that the vertical position of the rocket increases by one (almost) constant from one frame to the next. In physics, we call it “constant velocity.” Since this is a graph of position versus time, the slope of the line will be equal to this constant vertical velocity. From the chart above you can see this sets the rocket’s launch speed to 192 meters/second (m/s). That’s pretty fast – but is that fast enough to actually reach space? The answer is both yes and no. Here’s why.
Let me give a brief overview of exit velocity. Suppose you take an apple and throw it into the air with a velocity of 10 meters per second. (That’s pretty fast for an apple.) As the apple moves upwards, it slows down. Eventually, thanks to gravity, it will stop and then start falling back to Earth.
But suppose the apple is moving super fast, at 11,186 km lip seconds. Then it would be high enough that gravity wouldn’t be strong enough to stop it. That apple will come out.
Buzz Lightyear’s rocket is fast — but not that fast. Remember, we have calculated that it is moving at 192 meters per second. But that’s not the point, because you don’t need to worry about exit velocity if you have a rocket. The engine will continue to push the spacecraft to overcome that drag and keep it moving at a constant speed, so it won’t fall back to Earth.
In the case of the Buzz rocket, there are essentially three interacting forces throughout this part of the motion. First, it’s the thrust from the engine. A conventional chemical engine ignites propellants to produce exhaust gases. All forces act in pairs, so when the exhaust is pushed out of the engine, it pushes the rocket in the opposite direction. (The cool thing about rocket engines is that they work both in Earth’s atmosphere and in space, where there’s no air.)
The other two forces on the spacecraft are gravity downward because it interacts with Earth and air resistance pushing in the opposite direction of the spacecraft. Air resistance is caused by the collision between the rocket and the air.
As the spacecraft leaves the ground, both of these forces will eventually become insignificantly small. That’s because moving further away from the center of the Earth means that the strength of gravity pulling on the ship decreases. And once the rocket is out of the atmosphere, there will be no more air drag, because there won’t be any air. The only force left will be thrust from the engines, so the speed of the spacecraft will increase.
But… this is not how rockets actually work. Normally, rocket engines generate thrust of bigger than gravity. This means that an ascending rocket will Urge and not just going at a constant speed.
