Newton’s First Law of Motion

• Krishna Gopal Shrivestava of India set an unofficial world record in 1999 by pulling a ship with a mass of 244,000 kg with his teeth. We can use this feat to learn about force, mass, and acceleration.

1. How would a small rowboat be different if Shrivestava pulled it rather than a large ship?

2. In what direction did the ship move? Why do you think so?

3. When Shrivestava stopped pulling, did the ship stop moving? Explain.

Famous ScientistsThe Laws of Motion

Great ideas on motion!

Section 1: The First Law of Motion

Objectives:• Define Newton’s first law of motion.• Explain how inertia and mass are related.

Aristotle (300 B.C.) Greece

• His ideas were popular for ~2,000 years.

• Now, his ideas are obsolete.

• 2,000 years of false knowledge

What Aristotle said:

• Heavier objects fall faster than lighter ones

• Earth is the center of the universe

• All motion on Earth is straight and linear

WRONG!!

Aristotle (300 B.C.) Greece (cont.)

Aristotle’s ideas about motion were a beginning in scientific thought.

Galileo Galilei (1600’s) Italy• Discovered moons of Jupiter• Supported the idea that planets revolve around the

Sun• Famous for ideas on motion…but these were not

readily accepted in his time

Galileo Galilei (cont.)

Galileo’s Ideas on Motion:

1. All objects fall at same speed (independent of weight)

2. Introduced concept of friction- which slows things down

3. Inertia (sluggish or lazy)- tendency of an object to resist a change in its motion

Sir Isaac Newton (1700’s) England

• “Father of Physics”– Devised calculus– Explained gravity, the

universal law of gravitation (apple on head?)

– Formulated a theory on the nature of light

– Formulated the laws of motion

Newton’s 1st Law of Motion

• An object at rest remains at rest…• An object in motion maintains its velocity…• Net force = 0– balanced forces, no acceleration!

Unless it experiences an

unbalanced force

First Law (cont.): INERTIA

• Newton borrowed the idea from Galileo.• The inertia of an object is the tendency of the

object to resist a change in motion.• The larger the mass of an object, the greater

its inertia.

Newton’s 1st Law of Motion

Apply Newton’s 1st Law of motion to this picture:

Newton’s 1st Law of MotionSports Examples:• A moving ball will keep

moving forever. Unless slowed by external

force of friction (ground, floor) or gravity

• A soccer ball in grass remains stationary. Until it is kicked (external

unbalanced force)