During static friction, the two surfaces are at rest relative to each other: the atomic peaks rest in the troughs. It requires a certain level of force to deform the peaks sufficiently for the sliding to begin.
| Applications and Skills |
|---|
| Representing forces as vectors |
| Sketching and interpreting free-body diagrams |
| Describing the consequences of Newton’s first law for translational equilibrium |
| Using Newton’s second law quantitatively and qualitatively |
| Identifying force pairs in the context of Newton’s third law |
| Solving problems involving forces and determining resultant force |
| Describing solid friction (static and dynamic) by coefficients of friction |
| Understandings |
|---|
| Objects as point particles |
| Free-body diagrams |
| Translational equilibrium |
| Newton’s laws of motion |
| Solid friction |
$$ F = ma\\ F_f \le \mu_sR\\ F_f = \mu_dR $$
$$ \mu_s = tan\theta\\ \mu_s = \frac{F}{mg} $$
<aside> 🌐 Classical physics requires a force to change a state of motion, as suggested by Newton in his laws of motion.
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A force if a push or a pull. It is measure in Newtons (N). A force is a vector quantity, it means a force has a direction.
A free-body diagram is a diagram showing the magnitude and direction of all the forces acting on a chosen body. The body is shown on its own, free of its surroundings and of any other bodies it may be in contact with. We treat the body as a point particle, so that all forces act through the same point.
The rules for a free-body diagram for a body are the following: