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 than if Shrivestava
pulled it rather than a large ship?
2. In what direction is the ship
moving? Why do you think so?
3. When Shrivestava stopped
pulling, did the ship stop moving?
Explain.
Famous Scientists
The 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
WRONG!!
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
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 Motion
Sports Examples:
• A rolling ball keeps
rolling forever.
Unless slowed by external
force of friction (grass,
floor)
• A soccer ball in grass
remains stationary.
Until it is kicked (external
unbalanced force)