Transcript Chapter 2 Newton`s First Law of Motion

Chapter 2
Newton's First Law
of Motion - Inertia
1. ARISTOTLE ON MOTION
Aristotle attempted to
understand motion by
classification.
Two Classes:
Natural and Violent
Natural
Natural motion depended on
nature of the object.
Examples:
A rocks falls
Smoke rises
The falling speed of an
object was supposed to be
proportional to its weight.
Natural motion could be
circular (perfect objects in
perfect motion with no
end).
Violent
Pushing or pulling forces
imposed motion.
Some motions were difficult to
understand.
Example: the flight of an
arrow
There was a normal state of
rest except for celestial
bodies.
Aristotle was unquestioned for
2000 years.
Most thought that the Earth
was the center of everything
Littlefor
diditthey
it was
was know
in its that
normal
state.
Texas
No one could imagine a force
that could move it.
2. COPERNICUS AND
THE MOVING EARTH
Sun was center, not earth.
He was hesitant to publish
because he didn't really
believe it either.
De Revolutionibus reached
him on the day he died,
May 24, 1543.
3. GALILEO AND THE
LEANING TOWER
17th Century scientist who
supported Copernicus.
He refuted many of Aristotle's
ideas.
Worked on falling object
problem - used experiment.
4.
GALILEO'S INCLINED PLANES
Knocked down Aristotle's push or
pull ideas.
Rest was not a natural state.
The concept of inertia was
introduced.
Galileo is sometimes referred to
as the
“father of experimentation.”
He tested with planes.
Demo - Ball and Incline Plane
The change in speed depended
on the slope of the incline.

5. NEWTON’S FIRST
LAW OF MOTION
Newton finished the overthrow of
Aristotelian ideas.
Law 1 (Law of Inertia)
Every object continues in its state of
rest, or of uniform motion in a
straight line, unless it is compelled to
change that state by forces
impressed upon it.
“If you leave an object alone, it has
constant velocity.”
Demonstrations
Demo
Demo
Demo
Demo
Demo
Demo
Demo
- Weight and String
- Card, Cup, and Coin
- Swinging Rocks
- Coins on Elbow
- Table Setting
- Bottle, Hoop, and Chalk
– Lead Brick and Hammer
6. NET FORCE
A force or a combination of forces produces
changes in motion (accelerations).
10 N
10 N
10 N
20 N
m
=
m
10 N
=
m
10 N
=
m
20 N
0N
10 N
m
m
7. THE EQUILIBRIUM RULE
Examples of
Mechanical
Equilibrium:
Computer setting on a table
Scales pushing up
Normal up
Weight down
Weighing yourself on a set of scales
Hanging from a tree
Car parked on an incline
Friction
Tree
pulling up
Weight down
Normal
Weight down
Weight down
The Equilibrium Rule
F

0

8. SUPPORT FORCE
In the first example of
mechanical equilibrium the
table supplied a force upward
that was called the normal
force. It is a support force.
Normal up
Scales pushing up
Weight down
Consider the second example of
mechanical equilibrium. The
scales supply a support force
on the man.
Weight down
9. EQUILIBRIUM OF MOVING THINGS
Equilibrium is a state of no change.
If an object moves in a straight line with no change
in speed, it is in equilibrium.
Examples:
Driving at constant velocity
Normal up
Air resistance
Force from road
Air
Resistance
Weight down
Terminal velocity in parachuting
Weight down
10. THE MOVING EARTH
It is hard to detect the motion of the
earth because we are moving with it.
Early science could not predict large
enough forces to move the earth.
Can Hewitt’s bird drop down and catch
the worm if the Earth moves at 30
km/s?
Demo - Cart and Ball Launcher
Video – Snowmobile and Flare
Chapter 2 Review Questions
Which person below is most
highly recognized for proposing
a heliocentric universe?
(a) Aristotle
(b) Newton
(c) Galileo
(d) Copernicus
If an object weighs 10 lb, what must
the air resistance force be if the
object is falling and has reached
terminal velocity?
(a) 10 lb
(b) 32 lb
(c) there is no way of telling without
knowing what the value of the
terminal velocity is
Newton's concept of motion said that
the natural state of an object was
(a) constant velocity
(b) constant acceleration
(c) constant net force