SCIENCE (CURIOSITY) CLASS 8 SOLUTION

Chapter 5 – Exploring Forces (Class 8 Science | NEP 2025 Pattern)

🧭 Chapter Overview

Every time you throw a ball, open a door, or press a switch — you apply force.
Force is what makes objects move, stop, change shape, or direction.

This chapter, “Exploring Forces,” helps you understand how forces work, the types of forces around us, and how they are essential in both nature and technology.
By the end, you’ll see how invisible pushes and pulls shape everything — from the orbit of planets to the functioning of machines.


🎯 Learning Objectives (NEP 2025 Competency Table)

CompetencyLearning OutcomeNEP Skill
Conceptual UnderstandingExplain the meaning & types of forcesConcept Clarity
Analytical ThinkingIdentify forces in daily life situationsCritical Reasoning
ApplicationApply Newton’s laws to real examplesPractical Understanding
InquiryConduct experiments with springs & magnetsHands-on Learning
Ethical AwarenessUnderstand friction & its controlEnvironmental Awareness

⚙️ 5.1 What Is Force?

Definition:
A force is a push or pull on an object that can change its state of motion or shape.

AspectExample
PushKicking a football
PullOpening a drawer
TwistTurning a bottle cap

A force always acts when two objects interact.

SI Unit: Newton (N) — named after Sir Isaac Newton.


🌍 Effects of Force

Force can:

  1. Change the shape of an object (e.g., pressing a sponge).
  2. Change the state of motion — move or stop something.
  3. Change the speed or direction of motion.

Example:

  • A bat hitting a ball → changes both direction and speed.
  • Squeezing a rubber ball → changes shape.

⚡ 5.2 Forces in Daily Life

SituationType of ForceEffect
Writing with a penMuscularMotion
Falling appleGravitationalPulls toward Earth
Car brakesFrictionalStops motion
Magnet attracting nailsMagneticPulls metal
Balloon rubbed with hairElectrostaticAttracts paper bits

🧠 Activity – Push, Pull, and Twist

Aim: Observe effects of different types of forces.
Procedure:

  1. Push a table → it moves forward.
  2. Pull a chair → it moves backward.
  3. Twist a bottle cap → shape changes.

Conclusion:
Push, pull, and twist are all forms of force that cause motion or deformation.


🧲 5.3 Types of Forces

1️⃣ Contact Forces – Need physical contact

TypeDescriptionExample
Muscular ForceForce applied by musclesLifting, pushing
Frictional ForceOpposes motion between two surfacesBrakes, walking
Normal ForceSupportive force by surfacesBook resting on a table
Tension ForceForce through stretched stringRope in tug of war

2️⃣ Non-Contact Forces – Act from a distance

TypeDescriptionExample
Gravitational ForceEarth pulls everything toward its centerFalling objects
Magnetic ForceAttraction/repulsion between magnetsCompass needle
Electrostatic ForceAttraction/repulsion due to chargesRubbing balloon on hair

🧱 5.4 Force and Motion

Motion = Change in position of an object with time.
Force can start, stop, or change motion.

Example:

  • Pushing a stationary ball → starts moving.
  • Applying brakes → stops a moving vehicle.

⚙️ “Force gives motion its life — without force, everything would remain still.”


🌬️ Balanced and Unbalanced Forces

TypeDescriptionEffect
Balanced ForceEqual & opposite → cancel each otherNo change in motion
Unbalanced ForceNot equal → object moves or changes speedMotion occurs

Example:

  • Balanced: Book resting on a table (gravity down, table up).
  • Unbalanced: Pushing a trolley → starts moving.

🧭 5.5 Newton’s Laws of Motion (Simplified)

LawStatementReal-Life Example
1st Law (Inertia)Object remains at rest or motion unless acted upon by forceSeatbelt saves you when car stops suddenly
2nd LawForce = Mass × Acceleration (F = m × a)Kicking a football hard moves it faster
3rd LawEvery action has an equal & opposite reactionGun recoils when fired

💡 Newton’s laws explain every movement — from walking to rocket launches.


🧱 5.6 Friction – A Force That Opposes Motion

Definition:
Friction is a force that opposes motion between two surfaces in contact.

TypeExample
Static FrictionStanding still on the floor
Sliding FrictionRubbing two surfaces
Rolling FrictionBall bearings in wheels

🧪 Activity – Observing Friction

Aim: Compare motion on rough & smooth surfaces.
Process:
Slide a toy car on a table and then on sandpaper.
Observation: Car moves less on rough surface → friction higher.

Conclusion:
Friction depends on surface type and weight of the object.


⚙️ Advantages of Friction

✅ Helps in walking
✅ Enables vehicles to move
✅ Allows writing, holding, and gripping

⚠️ Disadvantages of Friction

❌ Causes wear & tear
❌ Wastes energy as heat
❌ Reduces efficiency of machines

💡 Reducing Friction

  • Apply lubricants (oil, grease)
  • Use ball bearings
  • Streamline designs (aeroplanes, ships)

🧲 5.7 Magnetic and Electrostatic Forces

Magnetic Force

Magnets attract metals like iron, nickel, and cobalt.
They have two poles — North and South.
Like poles repel, unlike poles attract.

Application:

  • Magnetic compasses
  • Electric motors
  • Cranes for lifting scrap metals

Electrostatic Force

Generated when materials are rubbed together.
E.g., rubbing a balloon on hair attracts paper bits.

Explanation:
Rubbing transfers electrons, creating opposite charges that attract each other.


🌍 5.8 Gravitational Force – The Universal Attraction

Every object attracts every other object with a force called gravity.

Discovered by Sir Isaac Newton in the 17th century.

  • Keeps planets in orbit around the Sun.
  • Keeps the Moon revolving around Earth.
  • Causes objects to fall downward.

Force of Gravity (F)=G×m1×m2r2\text{Force of Gravity (F)} = \frac{G \times m_1 \times m_2}{r^2}Force of Gravity (F)=r2G×m1​×m2​​

🌎 Gravity — the invisible glue of the universe.


🧠 HOTS (Higher Order Thinking Skills)

  1. Why can’t we walk properly on an oily surface?
  2. How do astronauts feel “weightless” in space?
  3. Why do vehicles use rubber tyres instead of metal wheels?
  4. Why is friction both a friend and a foe?
  5. If gravity attracts everything, why doesn’t the Moon fall onto Earth?

⚙️ NEP COMPETENCY FRAMEWORK

DomainNEP SkillReal-Life Application
ConceptualUnderstand forces and effectsPush/pull demo
AnalyticalDistinguish contact/non-contact forcesSorting game
PracticalConduct friction experimentToy car test
CreativeBuild working modelBalloon car / magnet toy
EthicalApply safe handling of forcesScience fair demo

💡 Memory Booster Box

🔹 Force = Push or Pull
🔹 Contact Forces → Muscular, Frictional
🔹 Non-Contact → Magnetic, Gravitational, Electrostatic
🔹 Balanced = No motion | Unbalanced = Motion
🔹 Newton’s Laws explain motion and inertia
🔹 Friction helps motion but causes wear


⚠️ Exam Alert Box

📍 Define: Force, Friction, Gravity
📍 Differentiate: Contact vs Non-contact forces
📍 Short Answer: Why does a ball stop rolling?
📍 Long Answer: Effects of force with examples
📍 Diagram: Magnetic field lines, forces on a table


📘 Quick Recap

✅ Force = push or pull that changes motion or shape
✅ Forces may be contact or non-contact
✅ Friction opposes motion and produces heat
✅ Magnetic and gravitational forces act from a distance
✅ Balanced forces cause no motion, unbalanced forces cause motion
✅ Newton’s laws explain the mechanics of everyday life


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