According to Newton's second law, acceleration is inversely proportional to the object's what?

• A. Mass
• B. Speed
• C. Time
• D. Radius

Answer: (A)

The relationship F = m a shows that for a given net force, acceleration decreases as mass increases. This is because acceleration is the rate at which velocity changes, and mass represents inertia—the resistance to that change. When you push on something with the same push, a lighter object speeds up more quickly than a heavier one because the heavier object resists changing its motion more. So, acceleration is inversely proportional to mass: if you double the mass while keeping the force the same, the acceleration halves.

Think of pushing a light cart versus a heavy pallet. The cart speeds up noticeably faster under the same push, while the pallet barely changes speed. Speed, time, and radius don’t set this direct relationship in the same way: speed is how fast you’re moving, time is how long you apply the force, and radius matters for circular motion via a different form of acceleration (a = v^2/r). The key idea here is that, with the same net force, heavier objects accelerate less because their greater mass produces greater inertia.