### Rolling balls and linear relationships

Spring 2012 laboratory 022 marked the fourth term of the even "no write up" laboratories. Assessment done spring 2011 indicated that the shift from writing up every laboratory to writing up only odd laboratories did not have a negative impact on the improvement in writing.
In laboratory 022 the location of the ball at each second is marked by a different student. Then the distance to the timing mark is determined. This makes the time the independent variable and the distance the dependent variable.
As this laboratory is often done in physics, the distance is preset and becomes the independent variable, with a timing determining the time to that fixed distance - such as a photogate on a air track. The ramp permits rolling the ball at a specific velocity that can be repeated. This allows the timing markers to stand near to the correct location for their particular number of seconds.

Only a single timer is actually needed, one student calls out the seconds while watching a stopwatch or other digital second timer.

In the 11:00 section a light breeze kept arcing the ball. The wind was a reversed rotor off the roof of the gym. This was turned into a tail wind by moving the sheet to the west side of the parking lot as seen below.

The laboratory was wrapped up by graphing the data in the field and discussing the resulting curves on the paper. The data was linear enough to run a visual best fit line and calculate the slope. Some rolls did slow down, and this could be seen in the data as well. This term I did not discuss the tangent as the instantaneous velocity.