AP Physics 1 / Unit 2: Force and Translational Dynamics
2.4 Newton's First Law
Notes
An object stays at rest or moves at constant velocity unless a net external force acts (inertia).
- Constant velocity means net force = 0.
Practice
A puck slides at constant velocity on frictionless ice. The net force:
No acceleration.
Passengers lurch forward when a bus brakes because of:
Bodies keep moving.
An elevator moving up at constant speed: tension compared with weight:
Net force zero.
Ready for more? Take the Unit 2 test.