The energy applied to an object that attempts to cause it to change its direction, speed, or motion is called:

• A. Thrust
• B. Drag
• C. Force
• D. Weight

Answer: (C)

A push or pull on an object is what causes it to change its motion. This interaction, called force, drives acceleration according to Newton’s second law: the net force acting on an object equals its mass times its acceleration. To change speed or direction, there must be a nonzero net force; how the motion changes depends on the direction and magnitude of that force.

In flight, you encounter various forces: thrust from the engine, weight due to gravity, lift from the wings, and drag from air resistance. These are all specific kinds of force, but the general term that covers any interaction capable of altering motion is force. Energy or work describes how much energy is transferred by a force as it acts over distance, not the basic cause of motion change itself.