Day 97: The Radial Acceleration Experiment and The Real-Time Force Diagram for a block on a Ramp

Advanced Physics:

As mentioned last week, today was a data gathering day for the radial acceleration experiment. The purpose was to determine the relationship between radial acceleration and tangential velocity.  They used a single photo gate (One Gate Timing) to measure the tangential velocity and a Vernier WDSS to measure the radial acceleration.  They set it up to measure only the x-axis acceleration.  The radius was held constant, but the experiment was completed at a second radius.  Here are a few clips of the data being gathered.

Tomorrow will be all WB’ing.


General Physics:

Today we reviewed a bit about drawing force diagrams with components.  So far, we had only worked on tension forces that had components.  Today we extended this to when we have an object on an incline.  Years ago at a Phox Share meeting, Dale Basler shared a demo using the Vernier WDSS to show the force diagram for an object on an incline.  The file is set-up with animated vectors to show the gravitational force, the normal force and a tension force, but they are really the accelerations in those directions.  It is really slick and does an excellent job of showing the kids how the forces (size and magnitude) change (or not in the case of the gravitational force) as the incline is increased.  Here is a clip of it in action.

Day 95: Circular Motion Force Diagram Assessment and Quantifying Radial Acceleration

Advanced Physics:

Today the students took an assessment on drawing circular motion force diagrams.  Here is what I gave them:

Screen Shot 2015-01-29 at 8.15.48 PM

You’ll see why tomorrow.

We also had a pre-lab discussion to develop and experiment that will allow us to quantify radial acceleration.  Through discussion, we arrived at looking at the relationship between radial acceleration and tangential velocity for a given radius.  Most kids decided that the radial acceleration would be affected by the angular velocity, the radius and the tangential velocity.  I asked if we could do an experiment where we varied the radius.  A few realized that it was not possible because varying the radius will also change the tangential velocity *if the angular velocity is not changed)… so simply moving out on the circular to change the radius also changes the tangential velocity.

Here is the experimental set-up being used:


That’s a Vernier WDSS zip-tied to a meter stick on our record players.  The tangential velocity will be measured using a Vernier Photo gate and One-Gate timing.  The students will do the experiment twice… a small radius and a larger one.  We did not get finished, so more data collection later.  Here is a screen shot on my own data:

Screen Shot 2015-01-29 at 9.53.01 PM