Final answer:
Mr. Jeff uses Conservation of Momentum when he jumps on a skateboard and uses a fire extinguisher to move. By expelling the contents of the extinguisher, he gains equal momentum in the opposite direction following Newton's third law.
Step-by-step explanation:
When Mr. Jeff jumps on a skateboard and uses the fire extinguisher to move, he exercises Conservation of Momentum to change direction and move back to where he started. The expelled contents of the extinguisher push Mr. Jeff in the opposite direction, according to Newton's third law, which states that for every action, there is an equal and opposite reaction. As the momentum of the extinguisher's contents is conserved in one direction, Mr. Jeff gains an equal amount of momentum in the opposite direction.
Conservation of momentum is a fundamental principle in physics that indicates the total momentum of a closed system is constant if no external forces are acting on it. It's essential for explaining why Mr. Jeff moves forward when he activates the fire extinguisher. The momentum of the combined system (Mr. Jeff and skateboard) before using the extinguisher is the same after using it, albeit in the opposite direction. Conservation of energy focuses on the total energy being consistent in a closed system, whereas friction is the resistance that one surface or object encounters when moving over another.