ASVAB (Armed Services Vocational Aptitude Battery)Mechanical Comprehension (MC)Easy
A large cargo ship uses a propeller to move through water. Which of Newton's Laws of Motion primarily explains how the propeller generates forward thrust?
- ANewton's First Law of Motion
- BLaw of Universal Gravitation
- CNewton's Third Law of Motion
- DNewton's Second Law of Motion
Show answer & explanationAnswer & explanation
Correct answer: C. Newton's Third Law of Motion
Newton's Third Law states that for every action, there is an equal and opposite reaction. A propeller pushes water backward (action), and the water, in turn, pushes the propeller (and thus the ship) forward with an equal and opposite force (reaction).
Why the other options are wrong
- A. Newton's First Law deals with inertia, not the generation of thrust.
- B. The Law of Universal Gravitation describes gravitational attraction, irrelevant to propeller thrust.
- D. Newton's Second Law relates force, mass, and acceleration (F=ma), which describes the *result* of the thrust, not its generation.
Newton's Third Law
States that for every action, there is an equal and opposite reaction. Forces always occur in pairs.
- Action-reaction pairs act on different objects.
- Explains propulsion in vehicles (rockets, propellers, jets).
- Forces are equal in magnitude and opposite in direction.
Memory trick: Inertia, F=ma, Action-Reaction: the 1-2-3 of motion.