AP Physics C: Predict the landing point of a ball rolling down and off of an elevated incline. (Note: We haven’t studied rotational energy yet. So their prediction will be further than the actual landing point. That’s part of my plan to motivate our study of rotation.)
After taking measurements and grinding through their calculations, they put their target on the floor and held their breath as the ball rolled down and off the ramp.
Yep. They were off by about half a length of paper.
“What’s going on? Were we supposed to account for friction? Air resistance? Did the mass actually matter?”
So I rolled a few other things off the ramp. The first being 3 steel balls of different sizes (front row in picture below).
And the all landed in exactly the same spot as the original ball. It was really amazing.
Then I rolled one of the hollow metal balls (back row, center). And it landed shorter.
“Wait, let me try that again.”
Still short. Then I rolled the hollow yellow ball and the ring. Both short.
Then I rolled the black disk. That landed between the other landing points.
Now everyone is thoroughly perplexed. I love rotation!
NGSS Science and Engineering Practices
#5. Using mathematics and computational thinking
AP Physics C: As a wrap-up for our energy unit, I challenged my students to predict where a ball would land after rolling off a propped-up table. I knew, however, that they would all overestimate the landing spot because they wouldn’t take into account rotational kinetic energy. And why would they — we haven’t talked about it yet! However, the failure of their current model motivates the development of a new one which includes rotational energy. Later, we roll different shaped objects down the hallway ramp and notice something interesting: