It's nice to have someone at home helping me write physics questions

I'll bet you're thinking my adult husband is my helper, right? Ha, kidding, I know none of you are thinking that.

It's this one!

She's as smart as she is funny, that's for sure.

First though, some back story. On Thursday my physics classes were studying relative velocities: how fast is car A traveling relative to car B, that kind of stuff. Which is pretty easy for everyone to understand, because you deal with it all the time when you're driving. If you're going 65 and the car in front of you is only going 60, you're going to be gaining on them at a rate of 5 mph. Easy.

We were doing this problem on the board about two trains. One train, train B, is traveling at a velocity of 90 km/h relative to the ground, which is written Vbg. The other train, train A, passes its 180 m length by train B in just 4 seconds. So it's going 180 meters per 4 seconds, which is 45 meters per second. That is the velocity of B relative to A, which is written Vba.

The problem, though, is asking us to find the velocity of train A relative to the ground. I write this on the board, because the kids have a knack for forgetting what we're doing, and turn to face the class.

They're looking at me and giggling, and I didn't understand what was going on. I turned slowly back to the board. I had written,

"What is Vag?" on the board.

"Don't erase it!" they shouted. "That's the funniest thing ever!!"

The worst thing is, they all have iPads and iPhones, so there's probably a pic or 100 out there. This is why you absolutely CANNOT be facebook friends with your students. It's just better to not know.

After the train question was a person on a moving walkway question (like the kind at an airport), and Nina wanted me to explain my drawing of a little person holding a suitcase with a JFK sign above his head. So I told her about what we were doing, and she sat down with some paper and started making up problems. She came up with one about a person walking the wrong way on a moving walkway. The walkway is moving at 2 meters per second to the right  relative to the ground, and the person is  walking 2 meters per second to the left relative to the walkway. How fast is the walker moving relative to the ground?

0 meters per second!

I told her that was an amazing question, and I might put it on the quiz. She said I should note that my 8 year old wrote it. Either she's hoping that will inspire them, or Maggie's love of humiliating people is rubbing off on her.