Club card flyer physics

Walking to school this morning, I noticed about a dozen club flyers sitting on the snow-covered street. Seeing scattered club cards on the street is not all that unusual--we live near a college, and even in the age of digiterati, some partays are still announced through cards, personal "invitations" so exclusive you have to bend down to pick one up to get in.

The young woman featured on some cards occasionally catches my eye, the incongruity of her clothing clashing with the cold pavement.

But not today.

Every single card was upside down, with the edges touching the ground, like this:



And if you think about it a moment, it makes sense, and if you think about it a moment more, you have a neat little trick for a physics lab.