Day 6

Wednesday, January 23, 2008

Announcements:

Today is the last day to make any registration changes without a Drop/Add form. If you wish to be registered for the special APPLES Service Learning section of this course (section 002), please let me know. APPLES forms are available for this commitment.

Assignments:

Answer the recommended conceptual exercises and problems for Chapter 3 (listed at the bottom of the daily schedule), and check your understanding by looking at the answers in the back of the textbook.
Read Chapter 4 and be prepared to discuss on Friday.

Class Discussion:

Chapter 3: How Things Move

Aristotelian thinking: objects move according to their "natural" motion. (rocks fall down, smoke rises, sliding objects stop moving)
Galilean and Newtonian physics: objects accelerate according to the net force acting on them.
Demo: penny and feather in vacuum, book and paper drop (example of "drafting")
Inertia - the tendency for objects with mass to maintain their velocity (which may be zero).
Demo: table cloth and dishes

Displacement (a vector) is the change in position of an object
Distance (a scalar) is the total length traversed by an object.
Average velocity = displacement/time interval
(Instantaneous) velocity: v = dx/dt
Speed (a scalar) is the magnitude of the velocity (a vector)
Average acceleration = change in velocity/change in time
(Instantaneous) acceleration: a = dv/dt
The magnitude of the acceleration does not have a special name.

Example: Walk forward 3 m and back 3 m in 3 sec. What are the above quantities?

Concept questions using clickers.

Exercise: A car accelerates from 0 to 30 m/s in 6 seconds
- Sketch the position versus time graph
- Sketch the velocity versus time graph
- Sketch the acceleration versus time graph

Draw a graph of vertical velocity as a function of time for a ball thrown up to a height of 5 m and then caught.

Useful Kinematics Equations:
    The final speed of an object moving with constant acceleration is: vf = a*t
    Distance traveled for object moving with constant acceleration: d = 1/2a*t^2 + vo*t
    Combining the above equations and eliminating the time gives: (vf)^2 = (vo)^2 + 2*a*d

Demo: How can a meter stick be used to measure a person's reaction time?

Demo: Ramp with blinking lights
    What is the acceleration of the balls rolling down the ramp?
    If a ball is pushed up the ramp, what will be its acceleration as it moves up and then down the ramp?

Demo: falling water drops