Forces and Newton's Laws
Dynamics explains motion through forces, which are pushes or pulls represented as vectors with magnitude and direction.
| Law | Definition | Key Rule |
|---|---|---|
| First Law (Inertia) | Objects keep constant velocity unless acted on by a net force. | Motion needs no force to continue; only change does. |
| Second Law | (Net force equals mass times acceleration). | It is a differential equation driving trajectories. |
| Third Law | For every action, an equal and opposite reaction. | Action-reaction pairs act on two different objects. |
The net force is the vector sum of all forces governing motion.
Equilibrium and Pitfalls
An object in equilibrium experiences zero net force and zero acceleration, meaning it is either at rest or moving at a constant velocity. Common forces like weight (), tension, friction, and normal force combine vectorially.
Because forces are vectors, resolve them into components along chosen axes to apply Newton's second law component by component.
Common Pitfalls: - Thinking a force is required to keep an object moving. - Misapplying the third law by assuming action-reaction pairs cancel out; they act on different objects. Forces that cancel for equilibrium act on the same object.