Transcript Let`s Pause for Two Questions from the Audience

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NSTA Web Seminar:
Force and Motion: Stop Faking It!
Thursday, December 11, 2008
Force and Motion
Speed and velocity
Inertia and acceleration
Newton’s second law
Mass and weight
Speed and velocity
Which animal had the greatest average
speed for the entire race?
Tortoise
Hare
Which animal had the greatest
instantaneous speed during the race?
Tortoise
Hare
Definitions
Average
Instantaneous speed = speed
calculated over an infinitesimally
small time period
Which of the following is true?
All the balls moved
exactly alike.
All the balls moved
with the same speed.
All the balls were the
same color.
They weren’t really
balls, it’s a computer
simulation.
Let’s Pause for Two
Questions from the
Audience
Inertia and
Acceleration
Inertia = the tendency of an object
to keep on doing whatever it is
doing, whether in motion at a
constant speed or at rest
Acceleration = any change in speed and/or
direction
Let’s Pause for Two
Questions from the
Audience
Newton’s second law
Mass is a measure of inertia.
It’s just a number used to
compare inertias.
Newton’s second law
ΣF = ma
ΣF represents the net force acting on an
object.
m represents the mass of an object, which is a
numerical measure of its inertia.
a represents the acceleration of the object.
Let’s Pause for Two
Questions from the
Audience
24
Mass and Weight
25
Mass is:
Something you go to if you
are Catholic.
The amount of “stuff” in an
object.
A measure of an object’s
inertia.
A force that resists motion.
Weight is:
The gravitational force the
Earth exerts on an object.
The gravitational force any
object exerts on another
object.
The same as mass, but
with different units.
A good song by The Band
• Mass is a measure of inertia. It is the m that
goes into F = ma.
• Weight is the force that gravity exerts on
something. Weight is the F in F = ma.
The accelerations of the two objects are the same
For the large object:
F = ma
Weight of large object = (mass of large object)(acceleration of large object)
W = mg
For the small object:
F = ma
Weight of small object = (mass of small object)(acceleration of small object)
w = mg
Fgrav
Gm1m2

2
r
31
For an object near the surface of the
Earth:
F = ma
GmEarth mobject
rEarth
2
GmEarth mobject
2
Earth
r
 mobject aobject
 mobject aobject
GmEarth

a
object
2
rEarth
Thank you!
Let’s Pause for Two
Questions from the
Audience
Thanks to our presenter,
Dr. Bill Robertson, and
to NSTA Press for
sponsoring this program
http://www.elluminate.com
http://learningcenter.nsta.org
• NASA: Discover the Universe – From Galileo to Today
December 16, 2008
• NSTA Press: Picture-Perfect Science Lessons
December 17, 2008
• FDA: Teach Science Concepts and Inquiry with Food
December 18, 2008
http://learningcenter.nsta.org
National Science Teachers Association
Dr. Francis Q. Eberle, Executive Director
Zipporah Miller, Associate Executive Director
Conferences and Programs
Al Byers, Assistant Executive Director e-Learning
NSTA Web Seminars
Flavio Mendez, Senior Director
Jeff Layman, Technical Coordinator
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