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MassachusettsPhysics

Module 2: 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 can a diagram of the forces on an object reveal whether it is in equilibrium and what its acceleration will be?

Draw free-body diagrams showing all forces acting on an object, and use them to identify equilibrium (zero net force) and to find the net force in one direction (MA STE Introductory Physics, Motion and Forces).
A standard-level answer on free-body diagrams and equilibrium for the Massachusetts High School Introductory Physics MCAS: how to draw the forces on an object, what equilibrium means, and how to find the net force from a diagram.
12 min answer →

How do the gravitational force between masses and the electric force between charges depend on size and distance, and why are they so similar?

Describe Newton's law of gravitation and Coulomb's law, and use proportional reasoning to predict how the gravitational and electric forces change with mass, charge, and distance (MA STE Introductory Physics, HS-PS2-4).
A standard-level answer on Newton's law of gravitation and Coulomb's law for the Massachusetts High School Introductory Physics MCAS: how each force depends on size and distance, the inverse-square relationship, and how they compare under HS-PS2-4.
12 min answer →

Why does an object keep doing what it is doing unless a force acts, and what is inertia?

State Newton's first law, explain inertia as the resistance to a change in motion, and identify the role of balanced and unbalanced (net) forces (MA STE Introductory Physics, Motion and Forces).
A standard-level answer on Newton's first law and inertia for the Massachusetts High School Introductory Physics MCAS: why objects keep their state of motion, what inertia means, how mass measures it, and the role of balanced versus unbalanced forces.
11 min answer →

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

State and apply Newton's second law, F = ma, to calculate net force, mass, or acceleration, finding the net force first in multi-force situations (MA STE Introductory Physics, HS-PS2-1).
A standard-level answer on Newton's second law for the Massachusetts High School Introductory Physics MCAS: the relationship between net force, mass, and acceleration, the two proportionalities, and how to solve multi-force problems by finding the net force first.
12 min answer →

Why do forces always come in pairs, and why does a force pair not cancel out?

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 (MA STE Introductory Physics, Motion and Forces).
A standard-level answer on Newton's third law for the Massachusetts High School Introductory Physics MCAS: action-reaction pairs, why they are equal and opposite, why they act on different objects, and why they do not cancel.
11 min answer →

What are the everyday contact and gravitational forces, and how do weight, the normal force, and friction act on an object?

Distinguish weight from mass, calculate weight using Fg = mg, and describe the normal force and friction as the contact forces that act on objects on a surface (MA STE Introductory Physics, Motion and Forces).
A standard-level answer on weight, friction, and the normal force for the Massachusetts High School Introductory Physics MCAS: the difference between mass and weight, calculating weight with Fg = mg, and how the normal force and friction act at a surface.
12 min answer →