In which story does the quantities add to zero?
1.
MJ had a pool in her backyard that is 10 feet above sea level. Her friend threw a pool toy into the pool. She jumps 10 feet above the pool to get it. At what elevation is MJ at now?
2.
MJ had a pool in her backyard that is 10 feet above sea level. Her friend threw a pool toy into the pool. She dives 10 feet into the pool to get it. At what elevation is MJ at now?
1. In the first story, the quantities add to zero because MJ jumps 10 feet above the pool, cancelling out the 10 feet the pool is above sea level. So MJ is still at sea level.
2. In the second story, the quantities do not add to zero because MJ dives 10 feet into the pool, which does not cancel out the 10 feet the pool is above sea level. So MJ is at a depth of 10 feet below sea level.