1. Data Selection

2. Scenario
Sometimes an analysis does not apply to all of one’s data but to a selected range of the data or selected points from the data.
The techniques involved in Excel are easy – deleting or simply not selecting the undesired data or placing the mouse over a point on a graph to display its x and y components.

3. Example: Collision
We will use as an example the collision of two carts in an experiment that tests for the conservation of momentum.
A premise for conservation of momentum is that there is no external force, thus any part of the data with an external force being applied must be eliminated.

4. The experiment
In the experiment from which the example data is taken, a cart is pushed, then allowed to travel on its own for awhile before crashing into another cart to which it attaches.
The part of the data where the cart is pushed has an external force and must be eliminated before the analysis can proceed.

5. A plot of all of the data found in CartData.xls

6. The data up to about t=1.5 corresponds to the push and should be eliminated.

7. A simplified analysis
The data on the previous slide showed three distinct regions – before, during and after the collision.
A simplified analysis involves comparing the last “before” point with the first “after” point.
If one hovers the mouse over a point in an Excel graph, its x and y components are displayed.

8. Hovering over the last point before

9. Hovering over the first point after

10. After reading off and entering the velocity before and after, one can calculate the momentum before mass of cart 1 times the velocity before

11. And the momentum after is the sum of the masses times the velocity after.

12. And the Percent Difference is the difference divided by the average, formatted as a percent.