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Day 60: Another Single-Sentence Lab


AP Physics C: Yesterday I wrote about a single-sentence lab we did in College-Prep Physics. We also did a single-sentence lab in AP yesterday and today:

Determine the rotational inertia of a bowling ball using 2 different and independent methods.

NGSS Science and Engineering Practices:
#3. Planning and carrying out investigations
#4. Analyzing and interpreting data
#5. Using mathematics and computational thinking
#7. Engaging in argument from evidence

Day 55: Falling Rolls Class of 2015

AP Physics C: Falling Rolls Day! Here’s video from 2 of this year’s groups. We had some synchronization issues for their first drops, but they each nailed it on their second attempt:

Click for other years and link to the activity.

NGSS Science and Engineering Practices:
#2. Developing and using models
#5. Using mathematics and computational thinking

UPDATE: 2014 DEC 4

Physics teacher Dan Hosey shared his class’s results today. I like how they use rods to drop both rolls simultaneously!

Day 53: Bike Wheel Direct Measurement Video


AP Physics C: I had to leave early today, so AP Physics students practiced their rotational motion problem solving using this direct measurement video. Click picture above to view video (QuickTime).

Here’s the lab handout. (It is focused on rotational kinematics and energy because we haven’t done torque and Newton’s Second Law for Rotation yet.): LAB DMV Bike Wheel Energy 2015 (word)

NGSS Science and Engineering Practices:
#4. Analyzing and interpreting data
#5. Using mathematics and computational thinking

Day 51: Rotational Kinetic Energy

AP Physics C: Today we derived the formula for rotational kinetic energy and showed that the total kinetic energy is simply the sum of the transnational and rotational energies. We teased out the relationships by analyzing the following 3 problems.

#1 Because we haven’t seen the rotational kinetic energy formula yet, they had to determine the linear speed of each sphere first for this problem:

2015 APC Energy Principle

#2. This one is easy.

2015 APC Energy Principle (1)

#3. For this one, they had to figure out the net velocity of each sphere.  The orange ones were easy. The blue ones were trickier (2D vectors!).

2015 APC Energy Principle (2)

And low and behold … all that crazy work to work out #3 turned out to yield the sum of #1 and #2!

NGSS Science and Engineering Practices
#5. Using mathematics and computational thinking

Day 45: Shoot For Your Grade


AP Physics C: Predict the landing point of a ball rolling down and off of an elevated incline. (Note: We haven’t studied rotational energy yet. So their prediction will be further than the actual landing point. That’s part of my plan to motivate our study of rotation.)

One group got resourceful and starting looking for help online. I thought my trick was going to be ruined, but when they did their calculations, they ignored the rotational energy term that was in the graphic they found. *whew*


After taking measurements and grinding through their calculations, they put their target on the floor and held their breath as the ball rolled down and off the ramp.


Yep. They were off  by about half a length of paper.

“What’s going on? Were we supposed to account for friction? Air resistance? Did the mass actually matter?”

So I rolled a few other things off the ramp. The first being 3 steel balls of different sizes (front row in picture below).



And the all landed in exactly the same spot as the original ball. It was really amazing.

Then I rolled one of the hollow metal balls (back row, center). And it landed shorter.

“Wait, let me try that again.”

Still short. Then I rolled the hollow yellow ball and the ring. Both short.


Then I rolled the black disk. That landed between the other landing points.

Now everyone is thoroughly perplexed.  I love rotation!

NGSS Science and Engineering Practices
#5. Using mathematics and computational thinking


Day 54: Real-Life AP Problem


AP Physics C: Today we applied our knowledge of rotational energy, projectile motion, and momentum to bring a 2010 AP exam problem to life. Although the actual values were different, the set-up was the same.

After some work…


… we tested our predictions: