Friday, November 14, 2008 - Block 4A

Collect Act-A-Graph Homework

Review Act-A-Graph Lab
Quiz on Act-A-Graph

Show problem solving strategy for distance,time,speed problems
Hand out worksheet on distance,time,speed problems
Have students work on it for 10 minutes - help students in need.

Tried talking about lab and what constant velocity looks like but could not get through to students. Gave up after asking what device you would use to measure distance and could not get an answer. Did not do lab.

Instead had student work on yellow worksheet of problems. Many students refused to follow the problem solving strategy despite my best efforts. Went around room to help students work on problems but many did very little work. I collected the yellow sheet at the end of the period and assigned the white sheet for homework.

What should have been a wonderful lab just did not work out. Bummer.


Constant velocity: What does constant velocity look like?
a) Straight line on distance vs time graph (slope gives speed)
b) Horizontal line on velocity vs time graph
c) If you took snapshot photos at regular increments and joined them all together, there would be equal spacings between the images
d) Strobe photo - again, equal distances in equal times.
e) Ticker timer, equally spaced dots. Closer together, less distance in the same amount of time (moving slower). Farther apart, more distance in the same amount of time (moving faster).
f) If you took a stopwatch and recorded the positions at equal increments of time you would find it moves equal distances.
g) Motion detector - gives straight line

Explain Ball Rolling Off Table Lab.
The horizontal speed doesn't change. Amazingly enough, it takes the same amount of time to fall straight down, as it does if the ball is rolling off the table and has some horizontal speed. The time to fall is given by t = sqrt( 2 * h/9.8). The horizontal distance the ball travels while falling is d = vx * t fall. If you accurately measure the height the ball falls, and the constant speed of the ball, you can predict where the ball will hit the floor. This is the challenge. You get one try.

Lab write-up: Name, Partners, Date
Title - Ball Roll Off Table
Introduction: Explain in words how you measure the speed and how you keep the speed constant from run to run.
Data Table: Make a data table of all data and averages
Calculations: Show your calculation for time it takes the ball to fall. Show the equation, plug in values, show result with units.
Show your calculation for the horizontal distance the ball moves through the air. Show the equation, plug in values, show result with units.
Conclusion: Give the result (did you land within the circle, if not, what went wrong?

Do Lab - one try. Record constant speed. Check with motion detector.