Earphone definition, a sound receiver that fits in or over the ear, as of a radio or telephone. See more.
Answer Wiki. If a rocket went straight up, it would either continue in that direction and leave Earth, or it would fall back down, depending on its velocity. Most rockets intend to enter orbit, which is an elliptical trajectory, and it's much more efficient to arc into this trajectory than to go straight up and then accelerate laterally.
By virtue of the law of conservation of momentum, the total momentum of the rocket and fuel must remain zero. The momentum of the escaping gases is regarded as having a negative value because they travel in a direction opposite to that of the rocket's intended motion.