Tues Feb 8, 2011

HW for tomorrow:
Do problem sheet on uncertainty (omit min max)
Do Quia on uncertainty

Check for textbook covers.
Collect Parent Notification Forms
Collect Course Expectation Forms

Chastised students for not putting on covers or doing Quia

Students wrote density measurements on board:
Block Mass(g) Length(cm) Width(cm) Height(cm) Density(g/cm^3)

Are they the same? How close do they have to be to be considered the same?
All the blocks were made of the same material, Aluminum.
How can we tell if the measurements are "good enough"

Hand out Flow Chart 1.2
Random Errors
Show how to calculate the uncertainty for several measurements
unc = sum(|meas - avg)|/# measurements
We did this in the Measurement and Graphing Lab of IB Physics 1 (Diameter vs Circumference)
If all measurements are the same, uncertainty is 1/2 the reading error

Rules for uncertainty:
1. At most 2 sig figs in uncertainty
2. Quantity then has the same number of decimal places as uncertainty

Reading errors
1. For analog devices, uncertainty is 1/2 the scale division...but, you often have this same uncertainty at each end of a ruler so the uncertainty in the length is the scale division
2. For digital devices, uncertainty is scale division

Adding or subtracting quantities:
If you add or subtract values, you add the absolute uncertainties.
Showed example of finding perimeter of circle.

Method of Relative Uncertainty:
Derived the relative uncertainty equation for a rectangle.
Used this equation in several examples: Area of square, volume of sphere
Showed that the absolute value of the exponent becomes the coefficient for the relative uncertainty.
Did a weird example: Q = A^2 * B^(5/3) * C^(-10)/D^(3/7)
unc Q = Q * 2*uncA/A + (5/3)*uncB/B + 10*uncC/C + (3/7)*uncD/D

Using Excel for uncertainty calculations:
Students got laptops and pulled up Excel spreadsheet
Entered in headers and then data from density lab
Calculated density and uncertainty and wrote using correct number of significant digits.

Handed out notes and problems on uncertainty
HW students work these problems (except max min problems)
Do Quia on uncertainty