SS Day 10: Accident Analysis

Friday, 27 May 2014

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How heavy is my Jeep?

There are days when stuff goes so well — kids are amped up from an activity, you had fun doing it, and everyone learned something cool. Yeah, today was one of those days. Inspired by Frank’s post on Finding the Mass of My Car Using Newton’s Three Laws, we grabbed some bathroom scales, measuring wheels, and the keys to my Jeep.

Like Frank, we set up on a slight incline to cancel out the effects of friction. I tested several downhills on campus to find one where releasing the brake in neutral kept me stationary, but just barely. We found just the spot on the entrance road to campus.

For fun, the kids helped me take the roof down on the Jeep. We all piled in (6 kids plus me!) and drove very slowly to the front of campus. I let the kids take it from there. They had already brainstormed in the classroom what they needed to do outside. While out there, I took their direction. We were outside for about half an hour.

When we got back to the classroom, I locked them in there jury-duty-style and said to come get me when they agreed on a verdict. They brought me in about 10 minutes later and walked me through the explanation shown below (disclosure: I recopied their work because you know the kid who wrote it had the sloppiest handwriting of all time). Conveniently, we were done just in time for lunch.

Student calculations for the mass of my Jeep. Actual mass according to a website: about 2000 kg.

Student calculations for the mass of my Jeep. Actual mass according to a website: about 2000 kg.

If you think you want to do this with a regular year class, I recommend recruiting teachers so you have more cars per capita. My class of 6 was perfect for one vehicle. Also, if I were to repeat this, I’d definitely include friction rather than finding a downhill area so I could negate friction. Oh, and for those keeping score at home, the kids’ result was about 30% larger than the actual value.

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