Most current rockets are chemically powered rockets (internal combustion engines) that emit an exhaust gas. A chemical rocket engine can use solid propellant (as does the Space Shuttle's SRBs), liquid propellant (as does the Space shuttle main engine), or a hybrid mixture of both. A chemical reaction is initiated between the fuel and the oxidizer in the combustion chamber, and the resultant hot gases accelerate out of a nozzle (or nozzles) at the rearward-facing end of the rocket. The acceleration of these gases through the engine exerts force ("thrust") on the combustion chamber and nozzle, propelling the vehicle (in accordance with Newton's Third Law).