# Day 45: Shoot For Your Grade

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.)

One group got resourceful and starting looking for help online. I thought my trick was going to be ruined, but when they did their calculations, they ignored the rotational energy term that was in the graphic they found. *whew*

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.

“Hmm.”

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

Tags:

HS Physics Teacher constantly questioning my teaching.

### 5 responses to “Day 45: Shoot For Your Grade”

1. watermanphysics says :

THIS IS AWESOME! Physics C is a new course for me & my students – so this is a great spin (heh!) on projectile motion – will totally be doing this one soon.

• Frank Noschese says :

There’s a recent AP Physics C free response problem that’s similar. The ball lands in a cart and they have to calculate the cart’s speed.

• watermanphysics says :

Cool! I’ll use that as a follow-up question!

2. Joe says :

Thanks, Frank. What a great way to introduce rotation! I tried this last year for the first time. My students could not believe that I set them up for failure, but I promised them that they’d have a chance to redeem themselves with a do over at the end of the unit.