Old dogs shouldn't try new tricks in public
I've been doing conservation of energy with my first year classes, all three of them. The first time round can be a bit chaotic as I get my thoughts in order, the second is about right but by the third I'm not sure whether I said it to that class or one of the previous two. However, I do much prefer teaching smaller classes rather than big ones. 20 students all doing design experiments is just too many for me to handle. Today I was with class number 3 which happens to be the class that is in the middle of our block alphabet, most confusing. For the 3rd time in two days I explained how when a box is projected up a slope the KE is converted to PE so 1/2mv2 = mgh. So ar so good. Then I thought I'd spice it up by considering a constant Force pushing the block up the slope and proceeded to try to prove that the work done (Force x distance moved) = mgh. After a couple of minutes of failure I gave up. Actually I could have spent the rest of my life trying to prove this and I never would have been able to, because it's wrong. I'd fallen into to the trap that I'm always warning my students about. Never predict the answer then try to work towards it because if your prediction is wrong you'll never get there. A constant force applied to the box will of course make it accelerate continuously.
Tags: energy