/sci/ - Science & Math

>>11580688
Cars actually do have thrusters. It's simply hard to visualize because when we imagine rockets we think of chemical rockets and it gets hard to discern fuel vs propellant.

It needs to be understood that when you're talking about vehicles, ANY VEHICLE, there is always fuel and there is always propellant.

Fuel is the thing containing energy that does work on the propellant to set it in motion.

Propellant is material which has work performed on it by the fuel to allow the vehicle to move.

In a chemical rocket, it's confusing because the fuel is also the propellant. Enthalpy is extracted from chemical fuel to heat its reaction products snd increase their pressure, causing them to shoot out the back.

HOWEVER, this is not a necessity. In a nuclear thermal rocket, for instance, the fuel is a solid core nuclear reactor and the propellant is hydrogen. The hydrogen gives no energy, only recieves it from the fuel and is accelerated out the back.

With a car, the fuel is gasoline or a battery and the propellant is indeed the earth. If it gains momentum by spinning its wheels, it is also imparting the same amount to the earth as spin in the opposite direction. The moment you hit the brakes, you decelerate the earth back to stationary in your original reference frame and the earth decelerates you back to zero as well.

Of course, if you accelerated until you had 1000 kilogram meters per second of momentum then the earth will have -1000 kilogram meters per second of momentum, and given how much the earth weighs it's an insignificant amount of velocity.

In this gif, the propellant is the canoe and the fuel is food energy.