Wednesday, Feb 18, 2009 - Block 3

Class started slowly with several students out giving blood.

Handed back RA 11.1 and asked if there were any questions. I graded the RA part out of 10 and assigned a grade for the problem part. There were 5 answers so I graded it out of 5.

Reviewed and finished problem of block bobbing in water.

Drew sketches of x, v, and a for SHM and showed that the slope of the displacement gives the velocity and the slope of the velocity gives the acceleration.

Covered energy in SHM. Showed that the elastic PE is given by 1/2 k x^2.

E total = 1/2 k x^2 + 1/2 m v^2 = 1/2 k A^2 = 1/2 m vmax^2

Drew sketches of E vs x.
Students calculated the value of x for which KE = elastic PE.

Did problem of SHM with tunnel through the Earth. Showed that the period is 84 min so that you get from one side to the other in 42 min.

Finished class by describing the IB lab - What are the factors that affect the period of a pendulum.

The design part must be done individually and is due on Friday. After that, students may work with a partner for the data collection. I instructed the students to think about using the Vernier lab equipment for data collection. Students will have to design their own pendulums.

Asked students to continue working on the remainder of the problems on the SHM problem sheet.

Test early next week.

Spring constant lab due tomorrow.