# 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 54: Kinetic Friction

*College-Prep Physics:* Last Thursday, students investigated the factors that might affect kinetic friction and how kinetic friction compares to static friction.

Today, students looked at the relationship between normal force and kinetic friction. Is the relationship proportional, like our previous experiments with static friction? If so, how do the slopes for kinetic friction compare to that from our static friction experiment?

*NGSS Science and Engineering Practices:
#2. Developing and using models
#3. Planning and carrying out investigations
#4. Analyzing and interpreting data
#5. Using mathematics and computational thinking
*

# 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 52: Balanced Forces in Motion

*College-Prep Physics:* We’ve been looking solely at forces in static cases. Now it’s time to look at moving cases. So I asked students to complete the following chart on a whiteboard:

What’s true about the forces in the constant speed cases? In the speeding up and slowing down cases?

Then I tried to address the misconception/difficulties kids have with constant speed = balanced forces (wouldn’t it just not move?) by demo’ing dueling fan carts. First with fan carts off, then with both on — what happens after I push?

*NGSS Science and Engineering Practices:
#2. Developing and using models
*

# 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:

#2. This one is easy.

#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!).

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 50: Poster Presentations

*College-Prep Physics:* Students presented their mini-posters to each other today. Although they worked in groups of three, I wanted each student to present their poster. So each person in a groups was assigned a number (1, 2, or 3). All the 1s presented to each other, all the 2s presented to each other, and all the 3s presented to each other. The students who were listening had a feedback rubric to fill out. To save paper, I turned the rubric into a Google Form and had students use iPads to complete a form for each poster presentation. Each student had 4 minutes 45 seconds to present, and then 15 seconds to move to the next poster. I used OnlineBoxingTimer.com to set up each “Round” and “Rest” time and projected it. (Last year I used the iPad app Circle Timer, but I like that this boxing timer is web-based.)

*NGSS Science and Engineering Practices:
#8. Obtaining, evaluating, and communicating information*