Is there an intuitive way to understand how parallax angle was first measured? Not driving d=1/p, but actually how the angle is attained? I get that baseline is 2 AU. But missing how the angle is physically measured or determined. #iteachphysics

Brain fart moment: given that KE=p^2/2m, one might think that since momentum is conserved in collisions, KE must be also (given constant mass). Is the fault here that p is a vector? I'm thinking of head on collision if equal carts moving at same speed so total momentum is zero. #iteachphysics

#iteachphysics, has anyone organized an AAPT F=ma exam contest at their school? I'm wondering what advice you'd have for someone considering it.