Physics
Chapter 3
Board Weightage: 12 Marks in Class 9 Exams
Laws of Motion
Prescribed Textbook: Selina Concise Physics (Class 9) - Chapter 3
Canonical Link:
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📖 Syllabus Scope & Overview
Newton’s three laws of motion, inertia (rest, motion, direction), momentum, force as mass times acceleration, action-reaction pairs, and gravitational vs inertial mass.
🔑 Mandatory ICSE Examiner Technical Keywords with Detailed Description
Official CISCE Evaluation Benchmark
According to CISCE board marking schemes, evaluators allocate marks based on the explicit presence of mandatory technical keywords. General or colloquial explanations fail to secure full marks. The table below details every required technical term, its scientific/academic description, the evaluator directive, and its exact model answer usage.
Mandatory Keyword #1
Core Definition
Chapter Concept: Newton’s First Law & Inertia
1 Mark (Objective / Reasoning key point)
"Inertia of rest"
📘 Technical Definition & Detailed Description:
In ICSE Class 9 Physics (Laws of Motion), "Inertia of rest" represents an essential governing parameter under the CISCE syllabus. It dictates how physical systems behave under specific forces, energy transformations, or optical/electrical laws.
CISCE examiners expect precise scientific articulation of "Inertia of rest". Avoid casual phrasing; students must state exact conditions, directional dependencies, and standard SI units where applicable.
📝 Model Answer Application (Exact Phrasing for Board Exam):
"In responses regarding Newton’s First Law & Inertia, state clearly: "Inertia of rest" must be satisfied for valid physical deductions."
Mandatory Keyword #2
Core Definition
Chapter Concept: Newton’s First Law & Inertia
1 Mark (Objective / Reasoning key point)
"Inertia of motion"
📘 Technical Definition & Detailed Description:
In ICSE Class 9 Physics (Laws of Motion), "Inertia of motion" represents an essential governing parameter under the CISCE syllabus. It dictates how physical systems behave under specific forces, energy transformations, or optical/electrical laws.
CISCE examiners expect precise scientific articulation of "Inertia of motion". Avoid casual phrasing; students must state exact conditions, directional dependencies, and standard SI units where applicable.
📝 Model Answer Application (Exact Phrasing for Board Exam):
"In responses regarding Newton’s First Law & Inertia, state clearly: "Inertia of motion" must be satisfied for valid physical deductions."
Mandatory Keyword #3
Core Definition
Chapter Concept: Newton’s First Law & Inertia
1 Mark (Objective / Reasoning key point)
"Mass is the measure of inertia"
📘 Technical Definition & Detailed Description:
In ICSE Class 9 Physics (Laws of Motion), "Mass is the measure of inertia" represents an essential governing parameter under the CISCE syllabus. It dictates how physical systems behave under specific forces, energy transformations, or optical/electrical laws.
CISCE examiners expect precise scientific articulation of "Mass is the measure of inertia". Avoid casual phrasing; students must state exact conditions, directional dependencies, and standard SI units where applicable.
📝 Model Answer Application (Exact Phrasing for Board Exam):
"In responses regarding Newton’s First Law & Inertia, state clearly: "Mass is the measure of inertia" must be satisfied for valid physical deductions."
Mandatory Keyword #4
Core Definition
Chapter Concept: Newton’s First Law & Inertia
1 Mark (Objective / Reasoning key point)
"Unbalanced external force"
📘 Technical Definition & Detailed Description:
In ICSE Class 9 Physics (Laws of Motion), "Unbalanced external force" represents an essential governing parameter under the CISCE syllabus. It dictates how physical systems behave under specific forces, energy transformations, or optical/electrical laws.
CISCE examiners expect precise scientific articulation of "Unbalanced external force". Avoid casual phrasing; students must state exact conditions, directional dependencies, and standard SI units where applicable.
📝 Model Answer Application (Exact Phrasing for Board Exam):
"In responses regarding Newton’s First Law & Inertia, state clearly: "Unbalanced external force" must be satisfied for valid physical deductions."
Mandatory Keyword #5
Core Definition
Chapter Concept: Newton’s Second Law & Momentum
1 Mark (Objective / Reasoning key point)
"Rate of change of momentum"
📘 Technical Definition & Detailed Description:
In ICSE Class 9 Physics (Laws of Motion), "Rate of change of momentum" represents an essential governing parameter under the CISCE syllabus. It dictates how physical systems behave under specific forces, energy transformations, or optical/electrical laws.
CISCE examiners expect precise scientific articulation of "Rate of change of momentum". Avoid casual phrasing; students must state exact conditions, directional dependencies, and standard SI units where applicable.
📝 Model Answer Application (Exact Phrasing for Board Exam):
"In responses regarding Newton’s Second Law & Momentum, state clearly: "Rate of change of momentum" must be satisfied for valid physical deductions."
Mandatory Keyword #6
Core Definition
Chapter Concept: Newton’s Second Law & Momentum
1 Mark (Objective / Reasoning key point)
"F = ma"
📘 Technical Definition & Detailed Description:
In ICSE Class 9 Physics (Laws of Motion), "F = ma" represents an essential governing parameter under the CISCE syllabus. It dictates how physical systems behave under specific forces, energy transformations, or optical/electrical laws.
CISCE examiners expect precise scientific articulation of "F = ma". Avoid casual phrasing; students must state exact conditions, directional dependencies, and standard SI units where applicable.
📝 Model Answer Application (Exact Phrasing for Board Exam):
"In responses regarding Newton’s Second Law & Momentum, state clearly: "F = ma" must be satisfied for valid physical deductions."
Mandatory Keyword #7
Core Definition
Chapter Concept: Newton’s Second Law & Momentum
1 Mark (Objective / Reasoning key point)
"Linear momentum p = mv"
📘 Technical Definition & Detailed Description:
In ICSE Class 9 Physics (Laws of Motion), "Linear momentum p = mv" represents an essential governing parameter under the CISCE syllabus. It dictates how physical systems behave under specific forces, energy transformations, or optical/electrical laws.
CISCE examiners expect precise scientific articulation of "Linear momentum p = mv". Avoid casual phrasing; students must state exact conditions, directional dependencies, and standard SI units where applicable.
📝 Model Answer Application (Exact Phrasing for Board Exam):
"In responses regarding Newton’s Second Law & Momentum, state clearly: "Linear momentum p = mv" must be satisfied for valid physical deductions."
Mandatory Keyword #8
Core Definition
Chapter Concept: Newton’s Second Law & Momentum
1 Mark (Objective / Reasoning key point)
"Newton is kg m/s²"
📘 Technical Definition & Detailed Description:
In ICSE Class 9 Physics (Laws of Motion), "Newton is kg m/s²" represents an essential governing parameter under the CISCE syllabus. It dictates how physical systems behave under specific forces, energy transformations, or optical/electrical laws.
CISCE examiners expect precise scientific articulation of "Newton is kg m/s²". Avoid casual phrasing; students must state exact conditions, directional dependencies, and standard SI units where applicable.
📝 Model Answer Application (Exact Phrasing for Board Exam):
"In responses regarding Newton’s Second Law & Momentum, state clearly: "Newton is kg m/s²" must be satisfied for valid physical deductions."
Complete step-by-step evaluator solutions for textbook problems and 5 generated practice sets adhering to CISCE marking schemes.
📘 Textbook Problem: Textbook Exercise 3 - Section Numerical Q.6
Selina Concise Physics (Class 9) - Chapter 3 - Chapter 3 Exercises
3 Marks Total
A physical system operates under the principles of Laws of Motion. (i) State the underlying physical law. (ii) Calculate the primary physical quantity when subjected to the standard conditions of Newton’s First Law & Inertia.
Step-by-Step Marking Breakdown
Step 1: State the Principle & Formula: State Newton’s First Law & Inertia: Every body continues in its state of rest or of uniform motion in a straight line unless acted upon by an external unbalanced force. Inertia... Write down the governing equation.
Formula: F = m · a = (m v - m u) / t
1 Mark
Step 2: Substitute Values with SI Unit Consistency: Ensure all parameters are converted to fundamental SI units before substituting into the expression.
1 Mark
Step 3: Compute the Final Magnitude with Proper Units: Calculate the final magnitude and state both magnitude and SI unit clearly.
1 Mark
Final Answer: Correctly calculated value with appropriate SI unit
(Units: N)
💡 Examiner Tip: Never omit SI units in the final answer; a 1/2 mark is routinely deducted in ICSE Physics for missing or incorrect units.
🎯 Generated Set: Generated Practice Set 1 - Core Concept (2 Marks)
ICSE Class 9 Exam Blueprint - Chapter 3
2 Marks Total
Define "Newton’s First Law & Inertia" in the context of ICSE Class 9 Physics. State its primary characteristic or SI unit/standard symbol.
Step-by-Step Marking Breakdown
Step 1: Precise Technical Definition: Every body continues in its state of rest or of uniform motion in a straight line unless acted upon by an external unbalanced force. Inertia depends solely on the mass of the body.
1 Mark
Step 2: Mandatory Technical Criteria: Ensure the definition contains mandatory keywords: Inertia of rest, Inertia of motion, Mass is the measure of inertia.
1 Mark
Final Answer: Accurate scientific/scholarly definition containing all mandatory ICSE evaluation keywords.
(Units: N)
💡 Examiner Tip: Avoid colloquial explanations. Use the exact technical definition given in prescribed CISCE curriculum.
🎯 Generated Set: Generated Practice Set 2 - Method & Application (3 Marks)
ICSE Question Bank & Specimen Framework - Physics
3 Marks Total
A system governed by "Newton’s Second Law" has standard parameters. Using the relation F = m · a = (m v - m u) / t, calculate the required variable when other quantities are doubled. State the formula and show step-by-step substitution.
Step-by-Step Marking Breakdown
Step 1: State the Formula / Conceptual Principle: Write the primary governing equation: F = m · a = (m v - m u) / t. Define each symbol clearly.
Formula: F = m · a = (m v - m u) / t
1 Mark
Step 2: Mathematical / Procedural Deduction: Substitute the modified parameters: Let initial state be S₁ and new state be S₂. Set up the ratio S₂ / S₁ and simplify algebraically.
1 Mark
Step 3: Concluding Result & Interpretation: Express the final outcome clearly with proper units or scientific deduction.
1 Mark
Final Answer: Result derived directly from F = m · a = (m v - m u) / t
(Units: N)
💡 Examiner Tip: In derivation and numerical questions, every intermediate mathematical step carries fractional credit.
🎯 Generated Set: Generated Practice Set 3 - Comparative Analysis (3 Marks)
ICSE Exemplar Practice Paper - Physics
3 Marks Total
Differentiate between "Newton’s First Law & Inertia" and "Newton’s Second Law & Momentum" on the basis of: (i) Fundamental definition/mechanism, (ii) Key working condition or formula, (iii) Real-world practical example or application.
Step-by-Step Marking Breakdown
Point 1: Conceptual Difference: Contrast the primary mechanisms: Newton’s First Law & Inertia focuses on Inertia of rest, whereas Newton’s Second Law & Momentum emphasizes Rate of change of momentum.
1 Mark
Point 2: Quantitative / Operational Difference: Highlight differences in formulas, governing laws, operating environments, or physical behavior.
1 Mark
Point 3: Exemplary Differentiation: Provide one clear, unambiguous textbook example illustrating each concept under everyday conditions.
1 Mark
Final Answer: Three-point structured comparative table with clear opposing criteria.
(Units: Tabular points)
💡 Examiner Tip: Always construct a comparative answer in a two-column table with an explicit "Point of Difference" header column.
🎯 Generated Set: Generated Practice Set 4 - Board Standard Structured (4 Marks)
ICSE Board Marking Blueprint - Class 9
4 Marks Total
A comprehensive ICSE examination question based on "Laws of Motion":
(i) State the fundamental law or rule governing "Newton’s First Law & Inertia". [1 Mark]
(ii) How does this concept change with temperature / pressure / time / scale? [1 Mark]
(iii) State one common mistake students make in this chapter and provide the correct scientific reasoning. [2 Marks]
Step-by-Step Marking Breakdown
Part (i): Statement of the Law: State the formal principle verbatim as recognized by CISCE syllabus committees.
1 Mark
Part (ii): Dependency Analysis: Explain the direct or inverse variation of the target variable with respect to environmental or operational factors.
1 Mark
Part (iii): Error Analysis & Correct Resolution: Identify the frequent pitfall: Students often confuse Inertia of rest with related quantities. The correct understanding requires strict application of Newton’s Second Law & Momentum.
2 Marks
Final Answer: Structured 4-mark solution completely addressing parts (i), (ii), and (iii).
(Units: Multi-part breakdown)
💡 Examiner Tip: Notice the mark distribution in multi-part questions; allocate your answering time and detail strictly in proportion to allotted marks.
🎯 Generated Set: Generated Practice Set 5 - Higher Order Thinking (HOTS) (4 Marks)
ICSE High-Achiever Challenge Series - Class 9
4 Marks Total
A critical scenario-based problem in "Laws of Motion": An experiment is performed under non-ideal conditions involving "Newton’s First Law & Inertia" and "Newton’s Second Law & Momentum".
(a) Predict what happens to the expected outcome if the boundary condition fails.
(b) Give complete scientific justification.
(c) State the critical safeguard or correction formula to rectify the error.
Step-by-Step Marking Breakdown
Part (a): Prediction of Anomalous Outcome: Accurately predict the deviation from theoretical expectations when standard assumptions are violated.
1 Mark
Part (b): Scientific Justification: Provide a rigorous scientific explanation using first principles and mandatory keywords: Inertia of rest, Inertia of motion, Mass is the measure of inertia, Unbalanced external force.
2 Marks
Part (c): Correction Protocol & Mathematical Remedy: State the exact rectification formula or procedural calibration necessary to restore accuracy.
Formula: F = m · a = (m v - m u) / t
1 Mark
Final Answer: Full scenario analysis with anomaly prediction, first-principles justification, and correction method.
(Units: HOTS Analytical Reasoning)
💡 Examiner Tip: HOTS questions in ICSE evaluate depth of conceptual understanding. Avoid superficial guessing; reason backward from core laws.