Monday, January 28, 2008
Announcements:
- Most everyone seems to be satisfied with the course
so far. Hopefully this cheerful outlook will not be spoiled by
the first exam, which is scheduled for next Friday, February 8.
In preparation for this exam, I encourage you to review the class notes
and problems, recommended questions and problems from the textbook, and
other conceptual exercises in the textbook. If you bought a new
copy of the textbook, you should also take advantage of the study
resources on the Textbook
Companion Website (access without a code is $42).
Assignments:
- Answer the recommended conceptual exercises and problems for
Chapter 4 (listed
at the bottom of the daily schedule), and check your understanding by
looking at the answers in the back of the textbook.
Class Discussion:
Chapter 4 - Why things move
Review: Concept questions
Demo: falling sticks
Demo: falling water drops
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