2/13 AP: p and K spreadsheet calculations

Today you will finish your spreadsheet calculations.

Remember, momentum is a vector, so some of your velocities will be negative. Be sure to include these, and that they match the relative directions of your carts.

• Start with one trial and:
  • Use formulas in the spreadsheet to calculate p, K, Δ , %, etc.
  • Once you have the trial with correct formulas, copy/paste those to all your other trials.
• For Δ in p and K, we always use (final-initial).
• For percent, we want to know the percent change, so use ( Δ / initial)
• Add some colors to make it easier to read

Averaging explosions calculations

Problem

Since we want to calculate percent as compared to the initial, and the initial p and K are zero, we can’t divide by the initial. Instead, use the following formula (all momentum values are the final values, since the originals are all zero)“

Solution

Rationale

Numerator: If momentum is conserved, then pa + pb should equal zero (one value being negative), so the numerator in our traditional change/original calculation would be zero.

Denominator: We would want the denominator to represent some value we are comparing to, so let’s chose the average of the two momenta…but since one is positive and the other is negative, we need to take the absolute value of each before averaging them.

And finally…

If your group was not able to collect any data, please use the following spreadsheet and save a copy for your group. bit.ly/VHSmomentum

Here’s a video about momentum and kinetic energy in car crashes for your enjoyment: