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```					“Do noW” TemplaTe             TAPE the note sheet you were
handed at the door into pg. of
The ancient Greeks concluded that it was
necessary to apply a continuous force to
keep an object in motion.
For example, if you set a book on a table and
give the book a quick push, the book slides
a short way then stops. To keep the book
moving, you need to keep pushing it.
The Greeks reasoned that the book stops
moving because you stop pushing it.
QUESTION
Based off of information you have learned, write a brief
paragraph letter to the Greeks, explaining what scientists
have discovered to help the Greeks understand why the book
stops moving.
A puck is moving on an
air-table. If the table is
so large that the puck
never hits an edge, what
will happen to the puck?
A      It will never stop.

B      It will stop in a short
distance.
C      It will speed up.
Galileo’s Thought Experiment

• Galileo thought of a different way to explain
the observation of the motion of the book.
• He imagined a world without friction and
conducted an experiment.

I doubt the Greeks’
idea! Suppose…
Galileo’s Thought Experiment

The rail is
horizontal…

If ball-bearing is   No force is needed to
released here…       keep the ball-bearing
moving.
…it will never rise up,
and will move at
constant speed.
horizontal rail
Galileo’s Thought Experiment

– In the absence of friction, a moving object will
continue moving even if there is no force acting
on it.
– In other words it does not take a force to keep an
object moving, it takes a force – friction – to stop
an object that is already moving.
Newton’s 1st Law of Motion
Description

Objects at rest remain at
rest, and objects in motion
remain in motion with the
same velocity, unless acted
upon by an unbalanced
force.
Newton’s 1st Law of Motion
LAW
Newton’s 1st Law of Motion

Inertia: Tendency of an
object to resist changes in
motion.
mass       inertia          Mass of an object is
resistance to             a measure of its
 start to move from rest        inertia.
 change moving speed
Which Has More Inertia?
Which is harder to push, pull, turn, or stop?!?
Newton’s 1st Law of Motion
Everyday Examples

Unbalanced Force

Unbalanced Force

Object in Motion
Object at Rest
Activity: (Name of Activity Station)

Observations:

Newton’s 1st Law!)
Exit Ticket
A ball is at rest on the floor of a car moving at a
constant velocity. What will happen to the ball
if the car swerves suddenly to the left?