If two forces of equal magnitude act on an object in opposite directions, what is the net force?

If two forces of equal magnitude act on an object in opposite directions, what is the net force?

• A. Zero
• B. Twice the force
• C. Equal to one of the forces
• D. Cannot be determined without mass

Answer: (C)

The main idea here is that the net force on an object is found by adding all the forces acting on it, taking direction into account. When two forces have the same strength but point in opposite directions, they cancel each other out, so the net force is zero. With no net force, Newton’s second law tells us the acceleration is zero, so the object doesn’t change its motion. If it’s at rest, it stays at rest; if it’s already moving, it keeps moving at the same speed and in the same direction. Mass doesn’t change that conclusion—the net force is zero regardless of the mass, so there’s no acceleration. The idea that the net force would equal one of the forces isn’t correct here, because the opposite, equal forces subtract to zero. Mass-only considerations don’t come into play for the net force itself.

The main idea here is that the net force on an object is found by adding all the forces acting on it, taking direction into account. When two forces have the same strength but point in opposite directions, they cancel each other out, so the net force is zero.

With no net force, Newton’s second law tells us the acceleration is zero, so the object doesn’t change its motion. If it’s at rest, it stays at rest; if it’s already moving, it keeps moving at the same speed and in the same direction. Mass doesn’t change that conclusion—the net force is zero regardless of the mass, so there’s no acceleration.

The idea that the net force would equal one of the forces isn’t correct here, because the opposite, equal forces subtract to zero. Mass-only considerations don’t come into play for the net force itself.