Roxanna Ahmadi, age 12, of Arroyo Grande, California, for her question:

How do rockets differ from missiles?

A rocket may be a missile and a missile may be a rocket. But not all missiles are rockets. A missile is any kind of object hurled at a target. A rocket is an object powered by the force of jet propulsion. An arrow is a missile, so is a stone thrown at a wall or other target. A bullet is a missile and so is a cannon ball. An arrow is sent on its way by a jerk from a bow string. Muscle power is used to hurl a stone. Gunpowder and other explosive materials are used to hurl bullets and cannons.

And modern warfare has discovered a more powerful force to hurl its missiles. It is a rocket that uses a continuing stream of exploding gases to jet itself forward. Rockets can carry bombs and jet propel them to their targets. These weapons are rocket missiles. But rockets also can be used to obtain the necessary velocities to place spacecraft in earth orbit or propel a spacecraft on a trajectory into deep space.   Rocket propulsion is explained by Newton’s third law of motion, “for every action there is an equal and opposite reaction”.