Revising my thinking: Force Tables

I've avoided force tables as a lab in the past. This is primarily because when I first started teaching physics and saw some collecting dust in the lab equipment room, the activities that were written for them seemed so formulaic that I was bored by them. I didn't know then what I might do to make it more interesting.

In making an activity using them today, I actually played around with them a bit. They are a bit tricky to set up, but once you have the weights balanced, it's oddly satisfying to see the ring in the center floating there:
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The theme of my lesson planning is a search for this type of gold: how can we play with this?

I've done activities involving 'find the unknown mass' before, and the force table offered an efficient way in to doing this.

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I asked students to figure out the mass of the weight circled in blue. I asked them to decide what information they needed to do so, and they requested the other two masses, which I provided.

Students worked quickly using their knowledge of forces and equations of equilibrium. They figured out pretty quickly that the angles between the threads were approximately equal, a fact I didn't notice until I looked from above:
Screen Shot 2014-10-11 at 11.12.34 AM

Their predicted answer of 290.9 grams was impressively close to the actual answer of 292.2 grams. We discussed that the assumption that the angles were the same might contribute for the error.

On the whole, this was a fun way to put to use a piece of equipment that I've kept out of my classroom for largely silly reasons. I think I'll definitely add this to the playlist for future units on equilibrium.

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