# Day 64: Collision Video Analysis

AP Physics C: Students used Logger Pro to do video analysis of 2 colliding dynamics carts. Each student in a lab group was responsible for analyzing a different video, then share out results and look for patterns.

The videos are here: Live Photo Physics Colliding Carts. We used videos #31, 32, 34, and 45.

Students are already familiar with collisions from physics last year. So this year, we are focusing on how the center of mass moves and how the carts move relative to the center of mass.

1. Create a graph showing the position of each cart and the position of the center of mass over time. Find slopes.
2. Create a second graph showing the position of each cart RELATIVE TO the center of mass over time. Find slopes.
3. Determine the total momentum of the system before and after the collision.
4. Determine the total kinetic energy of the system before and after the collision.
5. Determine the fractional change in internal energy of the system as a result of the collision.

CONCLUSION:

Compare/contrast your results with the others in your group:

1. Does the velocity of the center of mass remain constant always/sometimes/never?
2. In the center of mass reference frame, what do you notice about before/after velocities of each cart for elastic and inelastic collisions?
3. Is momentum conserved always/sometimes/never?
4. Is kinetic energy conserved always/sometimes/never?

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

#### About Frank Noschese

HS Physics Teacher constantly questioning my teaching.

### 6 responses to “Day 64: Collision Video Analysis”

1. Brock Baxter says :

Would anybody be willing to answer a few questions I have about analyzing “Angry Birds” and types of slow motion cameras to use in class?

• Frank Noschese says :

Sure. What questions do you have?

• Brock Baxter says :

My first question has to do with analyzing angry birds for my projectile motion unit. My goal is to compare the gravity to 9.8 m/s/s, but I’m unsure of the best way to go about doing that. Would you assume dimensions–diameter of bird, length of sling shot, etc.? Or would you convert pixels/s/s to 9.8 m/s/s and talk about sizes of the objects in the game vs. real life?

My second question is about high speed cameras. Do you use a particular one or does an iPhone suffice?

• Frank Noschese says :

I assumed the diameter of the red bird. It’d be interesting to see what sizes the students pick (humming bird, robin, chicken, etc) to see how that affects the resulting acceleration.

We have a discontinued Casio camera that does high speed. But it looks like the new iPhone camera can do the job, too.

• Frank Noschese says :

One more thing about Angry Birds: I had a student try different bird sizes until the acceleration was 9.8 m/s/s. Turns out the bird would need a diameter over 1 meter!

• Brock Baxter says :

Thank you for taking the time to reply.