What is Newton's First Law of Motion?

Newton's First Law states that a body remains at rest or in uniform straight-line motion unless acted upon by a net external force; this is called the law of inertia.

What is Newton's Second Law of Motion?

Newton's Second Law states that the rate of change of momentum of a body is proportional to the applied net force and takes place in the direction of the force, \(\vec{F} = \frac{d\vec{p}}{dt} = m\vec{a}\).

What is Newton's Third Law of Motion?

Newton's Third Law states that for every action there is an equal and opposite reaction; forces always occur in pairs acting on different bodies.

Inertia is the property of a body by virtue of which it resists any change in its state of rest or uniform motion in a straight line.

What is linear momentum?

Linear momentum \(\vec{p}\) of a body is defined as the product of its mass and velocity, \(\vec{p} = m\vec{v}\).

Impulse of a force is the product of force and the time for which it acts and is equal to the change in momentum, \(I = F\Delta t = \Delta p\).

State the law of conservation of linear momentum.

In an isolated system with no external force, the total linear momentum of the system remains constant during any interaction.

Write the mathematical form of Newton's Second Law for constant mass.

For constant mass, Newton's Second Law reduces to \(\vec{F}_{net} = m\vec{a}\).

What is an inertial frame of reference?

An inertial frame is a reference frame in which Newton's First Law holds, i.e., a frame that is either at rest or moving with uniform velocity.

What is a non-inertial frame of reference?

A non-inertial frame is a reference frame that is accelerating with respect to an inertial frame, in which fictitious or pseudo forces must be introduced to apply Newton's laws.

What is pseudo force?

Pseudo force is an apparent force introduced in a non-inertial frame of reference, given by \(\vec{F}_{pseudo} = -m\vec{a}_{frame}\), acting opposite to the acceleration of the frame.

Define normal reaction.

Normal reaction is the contact force exerted by a surface on a body, acting perpendicular to the surface.

Friction is the contact force that opposes the relative motion or the tendency of relative motion between two surfaces in contact.

What are static and kinetic friction?

Static friction acts between surfaces at rest relative to each other and can vary up to a limiting value, while kinetic friction acts when surfaces slide over each other with relative motion.

What is limiting friction?

Limiting friction is the maximum value of static friction just before the body begins to move relative to the surface.

NCERT Class 9 · Physics

True–False Booster – Laws of Motion

Sharpen your intuition about Newton’s laws, inertia, friction, momentum and equilibrium using exam‑style True–False statements with reasoning.

Each statement in this set targets a specific conceptual pitfall – ideal for last‑minute self‑check before school tests and Olympiad‑level problems.

Concept Drills Quick Revision Reasoning Practice

Jump to True–False Questions

Laws of Motion
True–False Lab

Inertia

Action–Reaction

Friction & Equilibrium

Momentum & Impulse

Quick Snapshot – Chapter at a Glance

Chapter

4 · Force and Laws of Motion

Focus Here

Concept traps in T/F questions

Best Use

Warm‑up before numericals & MCQs

Why Laws of Motion & True–False Matter

Board Exams & School Tests

Short True–False and reason‑type questions are common for quick concept checking.
Misconceptions about “force needed to keep motion” and “action–reaction” cost easy marks.
Clear ideas here make later topics like work–energy, gravitation and motion in a plane simpler.

Entrance & Olympiad Foundation

Competitive exams test subtle points on friction, pseudo‑force, equilibrium and circular motion.
Statement‑based MCQs often mirror these True–False ideas with “correct/incorrect” patterns.
Strong reasoning now becomes a backbone for Class 11–12 mechanics questions.

Key Concept Highlights Behind the Statements

Equilibrium & Inertia

Net external force zero implies zero acceleration, not necessarily zero velocity.
A body can be in uniform motion and still be in mechanical equilibrium.
True–False items here test your feel for “state of motion” vs “forces on it”.

Action–Reaction & Internal vs External

Action–reaction forces act on different bodies and never appear together in one FBD.
Internal forces cannot change total momentum of a system; only external forces can.
Many T/F items subtly mix up internal, external and interaction forces.

Friction, Pseudo forces & Circular Motion

Static friction is self‑adjusting; limiting friction and kinetic friction have fixed formulae.
In uniform circular motion on a flat road, static friction provides centripetal force.
Pseudo force and COM motion appear in advanced True–False practice for deeper insight.

Important Formula Capsules

Force & Acceleration

\(F = m a\)

Momentum

\(p = m v\)

Impulse

\(J = F\,\Delta t = \Delta p\)

Static & Kinetic Friction

\(f_{\max} = \mu_s N,\quad f_k = \mu_k N\)

Centripetal

\(a_c = v^2/R,\quad F_c = m v^2/R\)

Pseudo Force (Advanced)

\(\vec{F}_{\text{pseudo}} = -m\vec{a}_{\text{frame}}\)

You will apply these in statements about equilibrium, friction, collisions, pseudo forces and circular motion without heavy calculations.

What You Will Practise with These True–False Items

Recognise whether zero net force means “at rest” or “constant velocity” in different contexts.
Decide correctly if a given situation is in mechanical equilibrium or not.
Identify whether a statement about action–reaction is correct (same line, different bodies, equal and opposite).
Distinguish internal and external forces when talking about conservation of momentum.

Judge when static friction adjusts and when limiting or kinetic friction is being used.
Relate F–t and p–t graphs to impulse and force, and use them to interpret impact questions.
Understand advanced statements about pseudo forces, COM motion and constraints in string–pulley systems.
Spot incorrect generalisations such as “normal reaction is always equal to weight” or “friction is always opposite to velocity”.

Navigate to Detailed Laws of Motion Notes

Core Ideas

Forces, Friction & Motion

Revision & Practice

Exam Strategy – Using True–False for Laws of Motion

01

Always justify your choice. When you mark a statement True or False, write one line of reasoning (law, formula or example) – this trains you for “reason‑type” questions.
02

Watch for hidden words like “always” or “only”. Many false statements fail because they ignore special cases such as non‑inertial frames, non‑horizontal surfaces or presence of external forces.
03

Link each statement to a diagram. Draw a quick free‑body diagram or motion sketch for statements about friction, tension, circular motion or recoil before deciding True/False.
04

Group statements by concept. Solve all inertia/equilibrium items together, then all friction items, then momentum/impulse – this deepens pattern recognition for exams.
05

Use these as a daily warm‑up. Attempt 5–10 True–False questions each day before numericals; you will gradually eliminate typical misconceptions before the actual exam.

Before the Test

Revise three laws, definitions of momentum, impulse, friction and equilibrium.
Scan through your solved True–False set and re‑check the ones you got wrong earlier.
Quickly glance at the “Common Mistakes” list to avoid last‑minute slips.

Start True–False Practice

Scroll down to the True–False questions section below. Use the statements such as “A body can remain in uniform motion even when several forces act on it simultaneously”, “Static friction can adjust its magnitude up to a certain maximum value”, “In uniform circular motion on a horizontal road, static friction provides the necessary centripetal force” and many more to test your understanding one concept at a time.