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Mechanics: Forces and Newton's Laws

6 dot points across 6 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

How do you represent all the forces on an object and find the conditions for equilibrium?

Draw free-body diagrams showing all forces acting on an object, resolve forces into perpendicular components, and apply the equilibrium condition that the net force is zero in each direction.
A Regents Physics answer on free-body diagrams and equilibrium: how to draw all the forces on an object, resolve them into components, and apply the condition that the net force is zero in each direction for an object at rest or at constant velocity, with worked examples.
11 min answer →

How does friction depend on the surfaces and the normal force, and how do static and kinetic friction differ?

Describe static and kinetic friction, apply $F_f = \mu F_N$ to calculate the friction force, and use the coefficient of friction to compare surfaces and decide whether an object slides.
A Regents Physics answer on friction: the difference between static and kinetic friction, the meaning of the coefficient of friction, and how to apply the Reference-Table equation $F_f = \mu F_N$ to find the friction force and decide whether an object moves, with worked examples.
10 min answer →

Why does an object keep doing what it is doing unless a net force acts on it?

State Newton's first law (the law of inertia), relate inertia to mass, and apply the law to objects at rest and moving at constant velocity, recognizing that balanced forces produce no change in motion.
A Regents Physics answer on Newton's first law and inertia: what the law states, how inertia depends on mass, the difference between mass and weight, and how balanced forces leave motion unchanged, with worked examples and Reference-Table notes.
10 min answer →

How does the net force on an object determine its acceleration, and how does mass mediate that relationship?

State and apply Newton's second law, $F_{net} = ma$ , to calculate net force, mass or acceleration, and analyze situations with several forces by finding the net force first.
A Regents Physics answer on Newton's second law: the relationship between net force, mass and acceleration, why acceleration is proportional to net force and inversely proportional to mass, and how to solve multi-force problems, with worked examples and Reference-Table notes.
11 min answer →

Why do forces always occur in pairs, and why does a force pair never cancel?

State Newton's third law, identify action-reaction force pairs, and explain why the two forces in a pair act on different objects and therefore do not cancel.
A Regents Physics answer on Newton's third law: that forces occur in equal and opposite pairs, how to identify an action-reaction pair, why the pair acts on different objects, and why this means the forces never cancel, with worked examples and Reference-Table notes.
10 min answer →

How is weight related to mass and gravity, and how does a surface support an object?

Distinguish mass and weight, calculate weight using $F_g = mg$ , and determine the normal force on an object on a surface, including on a horizontal surface and an incline.
A Regents Physics answer on weight and the normal force: the difference between mass and weight, calculating weight with the Reference-Table equation $F_g = mg$ , and finding the normal force on level ground and on an inclined plane, with worked examples.
10 min answer →