# Day 94: Large-scale Qualitative Experiment for Newton’s 2nd Law

College Prep-Physics: In the hallway, we attached the hooked ends of the tow-rope to handles on large demonstration cart. Then we attached a large demo spring scale to the middle of the rope.

With one student sitting on the cart, we pulled with a constant 30 N. The student riding on the cart dropped blue boxes of tape each second. We used an iPad metronome app to keep time.

“What do you notice about the pattern of blue boxes? What does that tell you about the motion of the cart?”

“What could we change about the set-up so that the spacing of the boxes is different?”

Next, we pulled with 50 N, and the student riding on the cart dropped red boxes of tape each second.

“What do you notice about the pattern of red boxes? What does that tell you about the motion of the cart? How is it like the blue boxes? How is it different?”

“What else could we change about the set-up so that the spacing of the boxes is different?”

Finally, we added a second student to the cart and pulled with the original 30 N. One of the students dropped yellow packs of post-it notes each second.

“What do you notice about the pattern of yellow post-its? What does that tell you about the motion of the cart? How is it like the blue boxes? How is it different?”

Then we drew motion diagrams, position-time graphs, and velocity-time graphs for all 3 scenarios. We are just getting a feel for how force and mass affect acceleration, and the large-scale demo is memorable. Tomorrow we will use Desmos and PhET sim to determine a more quantitative relationship.

NOTE: I was originally going to have the student drop sugar packets — Regular (white), Sweet-n-Low (pink), and Equal (blue) — instead of the boxes. Turns out our school cafeteria only has regular sugar. So I improvised with the boxes of tape refills.

##UBFPM

#### About Frank Noschese

HS Physics Teacher constantly questioning my teaching.

### 2 responses to “Day 94: Large-scale Qualitative Experiment for Newton’s 2nd Law”

1. Andy Fitz says :

When you say a large demo spring scale, are you referring to something like this? http://www.pasco.com/prodCatalog/SE/SE-7349_demo-spring-scale/

Do you know where to find a good low friction cart?

### Trackbacks / Pingbacks

1. - February 26, 2014