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Day 105: Real-World Problem Solving (Dynamics)

College-Prep Physics: 

DO ANY TWO (in order of complexity)

1. Determine the starting and stopping acceleration of the elevator:

2. Determine the coefficient of kinetic friction between any two surfaces using only a meter stick, stopwatch, and a balance.

3. Determine the force of the slap shot:

Students were required to use the dynamics problem solving template. Sample work for each problem below:

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Day 103: Mythbusters + Always/Sometimes/Never

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College-Prep Physics: Students have been working on designing experiments to determine if the 3 myths above are always true, sometimes true, or never true.  And Veritasium’s newest video about numbers was the perfect introduction!

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Day 101: Dynamics Problem Solving Template

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College-Prep Physics: Introduced students to this problem solving template for multiple-step dynamics problems. Linking force concepts and motion concepts together can be tricky. I hope this sheet will help students organize their information.

You can get a Word version here: FMA Problem Template 2014

My template is influenced by similar templates from…

Knight (5 Easy Lessons)

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and Van Heuvelen (ALPS Kit):

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Day 97: What If There’s More Than One Force?

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College-Prep Physics: What if there’s more than one force? We used dueling fan carts and a motion detector to predict and test the outcomes of several scenarios. It turns out that …

2 carts, 1 fan on high (3F) ≈ 0.3 m/s/s

2 carts, 1 fan on medium (2F) ≈0.2 m/s/s

2 carts, 1 fan on low (1F) ≈0.1 m/s/s

So, what happens in the balanced cases?

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Not terrible surprising. How about the unbalanced cases?

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Then we returned to the PhET force and motion sim. We pushed the sleepy dog with 200 N (F1), turned friction on/off (F2), and looked at the resulting acceleratations:

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Then I challenged the students to determine:

  • When there’s friction, how hard should we push so that we get the same acceleration as without friction?
  • When there’s no friction, how hard should we push so that we get the same acceleration as with friction?

Students made their predictions and we tested using the simulation. Now we can modify the equation we derived yesterday and change force to net force.

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Day 96: Analyzing Simulation Data to Determine Newton’s 2nd Law

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College-Prep Physics: Today we shared out the results from Friday’s PhET Force and Motion simulation lab. Some students used Desmos to determine the line/curve of best fit, other did it manually (easy since the data is perfect). Then we tried to tease out what each of the constants in the 2 equations mean. (Here’s the one time where it’s more useful to express the slope as a fraction rather than a decimal.)

Day 95: PhET Force and Motion Lab

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College-Prep Physics: Students used the PhET Force and Motion simulation to design their own experiments to determine:

  • how force affects acceleration
  • how mass affects acceleration

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

From Skitch

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.

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