Welcome to the lesson on Force and Laws of Motion. In this chapter, we’ll explore how forces affect motion, and understand the famous laws of motion given by Sir Isaac Newton.
📘 What is Force?
A force is a push or pull that can:
🌀 Move a stationary object
🛑 Stop a moving object
⏩ Change speed of an object
🔄 Change direction of motion
📏 Change shape or size of an object
💡 Trivia:
Even pressing a doorbell applies force! 💥
⚖️ Balanced vs Unbalanced Forces
Balanced Forces – No change in motion
Unbalanced Forces – Cause motion or change
🧠 Newton’s Laws of Motion
1️⃣ Newton’s First Law – Law of Inertia
“An object remains at rest or in uniform motion unless acted upon by an unbalanced force.”
This property is called Inertia.
💬 Inertia is nature’s way of saying, “Let me relax unless you push me!”
📌 Examples:
🚌 You jerk forward when a bus suddenly stops
🏏 A ball lies still until hit
2️⃣ Newton’s Second Law – F = ma
The force acting on an object is equal to the product of its mass and acceleration.
Formula: F = ma
📌 Real-life Applications:
🧤 Soft hands reduce force while catching a ball
🧎 High jumpers land on cushions to reduce acceleration
🚗 Seat belts reduce sudden momentum
✅ Numericals:
Example: A 10 N force produces 2 m/s² acceleration. Find the mass.
3️⃣ Newton’s Third Law – Action & Reaction
“For every action, there is an equal and opposite reaction.”
📌 Examples:
🚶♂️ Walking: You push ground backward, body moves forward
🔫 Gun recoils after firing
🚀 Rocket pushes gas downward to lift up
🛶 Boat moves opposite when pushed
⚡ Momentum
Momentum (p) = Mass × Velocity
Measured in kg·m/s, it tells how much motion an object has.
✅ Numericals:
Example: A 4 kg object moves at 3 m/s. Find its momentum.
♻️ Law of Conservation of Momentum
“In a closed system, total momentum remains constant before and after interaction.”
📌 Applications:
🔫 Gun recoil
⚽ Football players colliding
✅ Numericals:
Example: Two trolleys collide — 8 kg & 4 kg. Find final velocity after they stick together.
📚 Quick Revision
🔹 Force: Push or pull
🔹 Inertia: Resists change (1st Law)
🔹 F = ma: 2nd Law
🔹 Action–Reaction: Equal & opposite (3rd Law)
🔹 Momentum: Conserved in collisions
💡 Quote: “Motion speaks physics. Newton gave it grammar.” 🧠
