Category: AP Physics 1

It looks like I’ll be back on Thursday. Still a rough throat, but the doc thinks I’ll be ready by then. I’ll probably have a wireless mic so I don’t have to strain my voice 😊 .

You might also find these instruction helpful.

I hope to post some videos showing how to solve yesterday’s assigned problems, but here are a few others that might be helpful.

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:

OK, unless I get hit by a truck, I will be back on Thursday.

Today, please work together to help all students complete their data collection and analysis Data analysis should include:

• Description of each type of collision/explosion you created.
• A list of the percent momentum and percent kinetic energy lost during each event.
  • Hint: Once you get your data entered into your spreadsheet, you should be able to calculate momentum and kinetic energy from the same cells for each event.
  • This is where consistency in your layout makes formula (equation) writing easy. Once you write the formula, just copy/paste to the needed cells.
• Calculate the average momentum and kinetic energy lost for all your events.

Remember to submit your spreadsheets below. I’m still missing a few.

My lengthy illness (severe sore throat, doc says it’s not coronavirus, but I did get tested for strep today) has presented an opportunity that I have always wanted to do, but never had the nerve to go through with:

Set a class to work on a topic and let them work it out with each other until they have it right, with no instruction from me (well, I have provided direct instruction last Monday and Tuesday, as well as some online videos and other tips).

I see you get down to work on whiteboards to solve problems from the book, but when you get your hands on equipment, many of you get frustrated when it gets hard.

Today’s the day to put all your brains together!

• If your group has a lot done, collaborate with other groups to help them along.
• Ask yourself what it is you are trying to measure, then decide how the equipment will get you that measurement.
• Don’t worry about making a mistake; you may have to repeat yourself, but you can’t really break the equipment.

In the end, if you can work your way through this somewhat complex experiment, the ‘grit’ and collaborative skills you develop will be much more valuable than any physics you learn in here.

Don’t give up! You are all intelligent people who can figure it out.

You’ve probably heard about grit and perseverance, but here’s a short video that you might want to watch for more info:

“Gritty people train at the edge of their comfort zone.”

Here’s a video to show you two different ways to think about momentum, using Newton’s laws and Galilean relativity.

Here’s one telling you all about the units and equation for momentum.