Newton’s Laws of Motion

 When a rocket lifts off it is because thrust exceeds the weight that keeps it in place.  This reflects Newton's First Law of Motion, which states that an object at rest will stay at rest as long as no unbalanced force is applied.  When a rocket reaches space, atmospheric drag (friction) is greatly reduced or eliminated.  No additional rocket thrust will be needed. Its inertia will cause it to continue to travel outward.

 Two forces act on a rocket being launched.  One is weight, the force generated by the gravitational attraction of Earth on the rocket.  The other is thrust, the force that moves the rocket.  Newton's Second Law of Motion applies here, as force (thrust) = mass × acceleration.  This formula can also be used to determine the rate at which a rocket accelerates, because acceleration = force/mass.

 The movement of the high-speed exhaust in one direction propels the rocket in the opposite direction.  This is Newton's Third Law of Motion in action; for every action there is an equal and opposite reaction.  Drag is the rocket's resistance to motion caused by the rocket's movement through air.  The nose cones of rockets are streamlined to help reduce drag.

 Rockets must be stable in flight — they must be able to fly in a smooth, predictable direction.  Fins help stabilize the rocket when air is present.  They are lightweight extensions attached to the exterior of the model rocket.  They streamline the flow of air and provide a large surface area and help to keep the center of pressure behind the center of mass of the rocket.