Question

Which situations contain unbalanced forces? Check all that apply.

A book rests on a table.
A book falls to the floor.
A car skids to a stop.
A duck floats on a pond.
A balloon hangs in midair.
A foam ball launches from a spring.

Answer 1

Unbalanced forces:
- A book falls to the floor (gravity produces a net downward force → acceleration).
- A car skids to a stop (friction produces a net force opposite the motion → deceleration).
- A foam ball launches from a spring (spring force produces a net force → acceleration).

Balanced (no net force):
- A book rests on a table (weight = normal force).
- A duck floats on a pond (weight = buoyant force).
- A balloon hangs in midair (weight = buoyant/tension force).

(Unbalanced forces mean a nonzero net force and thus a change in motion.)