Momentum

omentum is a property of all moving objects, including both aircraft and spacecraft. An object’s momentum is calculated by multiplying its mass by its velocity. Velocity is a vector-it has direction as well as size. Momentum, therefore, is also a vector.

A ball rolling down a hill gathers momentum as it goes faster and faster. A skydiver jumping out of a plane gath­ers momentum as gravity accelerates his or her rate of motion toward the ground.

Momentum depends on mass as well as speed, so a massive aircraft, such as a jumbo jet, has a lot more momentum

than a smaller, lighter plane flying at the same speed. If an aircraft speeds up, its momentum increases. If it slows down, its momentum decreases. When it lands and comes to a stop, its momen­tum falls to zero.