I’ve never really understood the physics of this. Obviously it works somehow — I’m not a moonlanding denier or anything — but my (admittedly primitive) brain continues to insist that a rocket thruster needs something to push *against* in order to work.
So what is it pushing against if space is essentially a void?
In: 7157
It is pushing against the particular of gas it is shooting out. Your rocket ships is jumping off the mass of the gas.
Imagine this. You are standing still on a skateboard and you throw a basketball in front of yourself. You will move backwards. Why? Because YOU are pushing off the mass of the basketball. Now imagine you basketball is full of water instead of air. Now imagine it is full of concrete or lead. Which makes you go further? Why? Well the heavier objects, because they have more mass and therefore more momentum. Now imagine the basketball is the earth. Why is it that you can jump against the earth? Because it has mass.
Now go back to the rocket ship. Imagine that each molecule of gas it pushes against pushes you a tiny bit in the opposite direction. Then look at how much gas comes out the back of a rocket!
Or consider a gun. When you shoot it, what happens? The gunpowder converts itself from a solid that takes up very little space into a gas which takes up a lot of space and it forces a bullet out the front. What is the bullet pushing against? Well the gas is pushing on the bullet and one the gun and you. You are pushed back a bit (recoil) because you are pushing against the bullet. Now imagine a gun that shoots blanks. You still feel recoils as the expanding gas pushes in all directions and leaves the muzzle. Now imagine a rocket is just a blank firing gun.
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