# Day 89: Intercepts

**Posted:**January 28, 2013

**Filed under:**School Days Leave a comment

The data for acceleration vs. speed for the spinning chairs was not super convincing in either of my classes, as far as trend goes. Linearizing to a quadratic didn’t ‘look’ much better than a simple linear function. Then I thought about intercepts.

The non-linearized intercepts were all something significantly non-zero; but if the intercept was non-zero, that would mean that we had an acceleration when the chair was at rest. By contrast, the linearized graphs had intercepts that made sense, very close to zero. This plus the fact that they did generally fit a bit better convinced students, I think, that acceleration is proportional to the square of speed. We then talked about how when you speed up just 10 mph going around a corner, the effect you feel seems to increase significantly, once again indicating something more than a linear trend.

We ended the day talking about how the direction of the force on an object is related to the direction of the acceleration, so we tried to make bowling balls move in circles.

Tomorrow we will investigate the effect of radius on acceleration, and we should be able to pull everything together on Wednesday.