Q1.
In such cases, what is the effect of forces when more than one force is acting on an object at rest or in motion?
Answer
Only the net force matters — the object behaves exactly as if that single net force were the only force acting on it.
- If the forces are balanced (equal magnitudes, opposite directions), the net force is zero. An object at rest stays at rest; an object already moving keeps moving with constant velocity. A ball floating on water is like this — the downward gravitational force and the upward buoyant force balance.
- If the forces are unbalanced, a non-zero net force acts. Forces in the same direction add; forces in opposite directions subtract, and the net force points along the larger one. The object then accelerates in the direction of the net force.
Same direction: net F = F1 + F2
Opposite directions: net F = |F1 – F2|, along the larger force
Opposite directions: net F = |F1 – F2|, along the larger force
Tip: when you push a box across a floor, the applied force and friction both act. The box moves only when your push is larger than friction, because only then is the net force non-zero and forward.