Wednesday, January 30, 2008
Announcements:
-
Focus The Nation is an unprecedented educational initiative on global
warming solutions for America
occurring at more than 1,000 universities and colleges and in all 50 states on
Jan. 31, 2008. As the largest teach-in in U.S. history,
Focus the Nation is
preparing millions of students to become leaders in the largest civilizational
challenge any generation has faced. For more information, please visit http://www.focusthenation.org
- Here is information about the events scheduled at UNC-CH for Focus the Nation today and tomorrow.
- The
most relevant event for this course is the tour of UNC's co-generation
power plant, which is one of the most efficient in the country!
You are encouraged to join this tour tomorrow at 10:00 am and
write a brief (half page) summary of what you learn for extra credit.
I will try to schedule another tour for our class later in the
semester when we study about electrical energy generators.
Assignments:
- Read Chapter 5 and come prepared to discuss in class on Friday.
Class Discussion:
Chapter 4 - Why things move
How is Newtonian thinking different from thought that preceeded
Isaac
Newton?
Newton's Laws of motion:
1) Inertia: A net external force is
required to change an object's velocity.
2) F = ma Why
does this equation make more sense written: a = F/m?
3) Action/Reaction: F12
= -F21 Equal and opposite forces on different objects.
Definition of mass - measure
of inertia, resistance to acceleration; measured in kilograms (kg)
Definition of force - a push or
pull, measured in Newtons (N). 1 lb. ~ 4 N
Draw a graph for the acceleration that results from force applied to a
mass (a vs. F). What does the slope represent?
Rocket Cart demo - Find the acceleration, the final speed, and
the force of each fire extinguisher.
Definition of weight and
"weightlessness": Fg = w =
mg
Ponderable: How can you reduce your weight?
Ponderable: How would you know the mass of an object in outer
space where there is no gravity?
How much would you weigh on the moon?
Show that objects in free-fall accelerate downward at a = g.
Normal force is the reaction
force that is exerted on an object and perpendicular
to a surface. Often Fn = -Fg, but not always.
Free body diagram practice: Forces
on a book
What is the net force on the car in Fig. 4.16?
Hands on friction - How does
it feel?
Applications of F = ma: clicker questions
Ponderable: What is the tension in the rope during a contest of
tug-of-war?
Demo: Fan cart with sail
Demo: Medicine ball with skateboards
Other questions?