Yesterday evening as I was driving through our little town, a pickup truck pulled into the lane ahead of me. The truck was piled with furniture, including a mattress. To be on the safe side, I changed lanes. Then the mattress fell out of the truck. The young woman driving pickup, backed up (in the street) to retrieve her mattress. I assumed she was a University student who was taking advantage of the plentiful seasonal garage sales to furnish her apartment.
Apparently, this student hasn't taken Physics yet.
The experiment was partially controlled. On the way home from my errand, I saw another pickup carrying a box spring, but this driver had tied down the load. The box spring stayed in the truck at least as long as I traveled near it.