Newton's First Law - Definition, Examples, Quiz, FAQ, Trivia

What is Newton's First Law?

Newton's First Law of Motion, also called the Law of Inertia, states that:

"An object at rest stays at rest, and an object in motion stays in motion at constant speed and in a straight line unless acted upon by an unbalanced force."

This means that objects will keep doing what they're already doing unless something changes their motion. If an object is sitting still, it will stay still. If it's moving, it will keep moving at the same speed and in the same direction.

Sir Isaac Newton described this law in 1687, building on ideas from Galileo Galilei. This law helps us understand why we need seatbelts in cars and why it's hard to stop a heavy object once it's moving!

Understanding Inertia

Inertia is the tendency of an object to resist changes to its motion. It's the reason why:

• A bowling ball is harder to move than a soccer ball
• A moving truck is harder to stop than a bicycle
• You feel pushed back in your seat when a car accelerates

Inertia comes from an object's mass. The more mass something has, the more inertia it has. This means heavier objects are harder to start moving and harder to stop once they're moving.

How Newton's First Law Works

Newton's First Law works through the balance of forces:

1. Objects at Rest: When an object is sitting still, all the forces acting on it are balanced. For example, a book on a table has gravity pulling it down and the table pushing it up with equal force.

2. Objects in Motion: When an object is moving at constant velocity (constant speed in a straight line), the forces acting on it are balanced too. For example, a spaceship in deep space far from any planets will keep moving forever because there are no forces to change its motion.

3. Changing Motion: When forces become unbalanced, the object's motion changes. This could mean starting to move, stopping, speeding up, slowing down, or changing direction.

Real-World Examples

We see Newton's First Law in action every day:

More examples of Newton's First Law:

• When you slide a book across a table, it eventually stops because of friction
• Astronauts float in space because there's no force to stop their motion
• Dusting a rug makes dust particles fly off because they resist changes to motion
• Your body keeps moving forward when a bus suddenly stops

Newton's First Law Quiz

Test your understanding with this quiz! Choose the best answer for each question.

Frequently Asked Questions

Here are answers to common questions about Newton's First Law:

Fun Physics Trivia

Discover some amazing facts about Newton's First Law and inertia!