Newton's Law of Motion
Table of Contents
Force
- Represents the push or pull applied to an object to change its motion or shape.
- Force is a vector quantity, which means it has both magnitude and direction.
- The SI Unit for force is Newton (N).
| Force | Symbol | Direction |
|---|---|---|
| Friction | \(F_f\) | Parallel to surface & opposite direction of sliding |
| Normal | \(F_N\) | Perpendicular to & away from th surface. |
| Spring | \(F_{sp}\) | Opposite the displacement of the object at end of spring. |
| Tension | \(F_T\) | Away from the object & parallel to spring, rope, or cable at point of attachment. |
| Thrust | \(F_{thrust}\) | In same direction as acceleration of object. |
| Weight | \(W\ or\ F_g\) | Straight down toward center of Earth. |
Action-Reaction Pairs
- Based on Newton's Third Law of Motion, all forces come in pairs.
- Interaction pair is composed of two forces that are in opposite directions and equal in magnitude.
First Law of Motion
- also called Law of Inertia
- An object at rest will stay at rest and an object at motion with stay in motion at constant velocity unless acted upon by external force.
Inertial Frames of Reference
- Any reference frame that is moving at constant velocity.
- "A frame of reference in which Newton's First Law is obeyed is called Inertial Frames of Reference."
Second Law of Motion
- also called Law of Acceleration.
\(a \propto\frac{F}{m}\)
- continues what the first law of motion told us. When a net force is applied, it produces acceleration.
- This law tells us that \(F = ma\) that came from \(F = \frac{d}{dt}(mv)\)
- Deriviation of SI Unit of force:
- \(1N = (1kg)(1 m/s^2)\) or
- \(1N = 1\frac{kg\cdot m}{s^2}\)
- Use \(kg\) for mass; weight in \(N\).
Third Law of Motion
- For every action, there must be equal and opposite reaction force.
- \(Action = -Reaction\)