Sort each situation by whether the NET force on the object is zero or nonzero.
Groups: Net force is zero · Net force is nonzero
- A ball at the top of its flight
- A train braking to a halt
- A skydiver falling at terminal velocity
- A satellite circling the Earth at constant speed
- A car cruising at a steady 25 m/s on a straight road
- A book resting on a table
Hints
- Zero net force means zero acceleration, at rest OR moving at constant velocity.
- Ask whether the velocity vector is changing in magnitude or in direction.
Show the answer
Net force is zero: A car cruising at a steady 25 m/s on a straight road, A book resting on a table, A skydiver falling at terminal velocity
Net force is nonzero: A ball at the top of its flight, A satellite circling the Earth at constant speed, A train braking to a halt
Uniform velocity, including the skydiver's terminal velocity, requires no net force at all, motion continues by inertia. The ball, the satellite and the braking train all have changing velocities, so each has an unbalanced force. Assuming that anything moving must be pushed is the pre-Newtonian instinct the first law overturns.
Practise Newton's Laws and Dynamics
The app has 6 more questions on this lesson, and keeps your place in the course. Mathematics I is free to start.
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