In our last class (which was a week ago), the Mechanics kids had whiteboarded a problem about a student jumping (which I got from Noah Segal, who—in addition to being a great physics teacher—is also a wizard of MS Word art):
The discussion (last class) was centered around the first situation. The original whiteboard showed the forces as balanced. Might be tough to see in this photo—sorry!
Some other students thought the normal force should be larger. Still others thought that the forces couldn’t possibly be unbalanced while the jumper’s feet are on the ground. How could the person be changing velocities if they aren’t in the air yet? Aren’t they still at rest?
During that class, it led to a student trying to jump without moving (hilarious—I love physics class!). During today’s class, we started out with a student setting up the force plate and jumping on it (we ran out of time for that last week).
I didn’t get a screenshot of the graph, but it was really convincing.