Chapter 4: Laws of Motion

4.1 Introduction

Key Idea: Forces are needed to change an object’s motion. Let’s break this down!

  • 💡 Force & Motion:
    • To move a stationary object (like a football), you need a force (e.g., a kick).
    • To stop a moving object (like a rolling ball), you also need a force acting against its motion.
  • 🤝 Contact vs. Non-Contact Forces:
    • Contact Forces: Require physical touch (e.g., pushing a stone, wind moving branches).
    • Non-Contact Forces: Act without touch (e.g., gravity pulling a falling stone, magnets attracting iron).
  • ❓ Big Question:
    • If a body is moving at a constant speed (e.g., a skater gliding on ice), does it need an external force to keep moving? (Hint: This leads to Newton’s First Law!)

Important for NEET:

  1. Force is required to change an object’s state (rest → motion or motion → rest).
  2. Forces can be exerted through contact (push) or at a distance (gravity, magnetism).
  3. Newton’s First Law (Law of Inertia) explains that objects in motion stay in motion unless acted upon by a force.

👉 Remember: A force doesn’t always need to be in contact with the object! Even the Earth’s gravity pulls you without touching you.