1. Introduction to Newton’s First Law
Newton’s First Law of Motion states:
“An object at rest stays at rest, and an object in motion stays in motion at a constant velocity unless acted upon by an unbalanced external force.”
This is also called the Law of Inertia because it describes how objects resist changes in their motion.
✅ Key Concept:
- If no force is applied, an object will not change its motion.
- If an object is moving, it keeps moving at the same speed and direction unless something stops or changes it.
2. Understanding Inertia
Inertia is the resistance of an object to changes in its motion. The greater an object’s mass, the greater its inertia.
📌 Examples of Inertia:
- A book lying on a table stays at rest unless you push it.
- A moving bus suddenly stops, and passengers lurch forward because their bodies want to keep moving.
- A rolling ball keeps rolling until friction or another force slows it down.
✅ Key Point: More mass = more inertia (harder to start or stop motion).
3. Real-Life Applications of Newton’s First Law
🚗 Seatbelts in Cars
- When a car stops suddenly, passengers lurch forward due to inertia.
- A seatbelt provides an external force to stop passengers safely.
⚽ Kicking a Ball
- A ball at rest stays at rest until you kick it.
- Once kicked, it keeps moving until friction or another force stops it.
🚀 Space Travel
- In space, there is no air resistance, so a spaceship keeps moving unless a force (like thrusters) acts on it.
4. Balanced vs. Unbalanced Forces in Motion
🔹 Balanced Forces:
- When forces on an object cancel out, there is no motion change.
- Example: A book on a table (gravity pulls down, the table pushes up).
🔹 Unbalanced Forces:
- When one force is stronger, it causes motion or change in motion.
- Example: A person pushing a shopping cart.
📌 Example of an Unbalanced Force:
- A soccer ball on grass stops because friction acts as an external force.
5. Key Takeaways
✔ Newton’s First Law (Law of Inertia) states that objects resist changes in motion.
✔ More mass = More inertia, meaning heavier objects are harder to move or stop.
✔ External forces (like friction, gravity, or a push) are needed to change motion.