Explain why there are two high tides per day at most coastal places, even though the Moon is on only one side of Earth. Step 1: The Moon's gravity is strongest on the near-side ocean, medium at Earth's centre, weakest on the far-side ocean. Step 2: Near-side water is pulled toward the Moon more than the centre is → bulge 1 facing the Moon. Step 3: Far-side water is pulled less than the centre → relative to the centre it lags behind → bulge 2 on the opposite side. Step 4: Earth rotates once in 24 hours beneath these two fixed bulges, so a coastline passes through both bulges → two high tides (and two low tides between them) per day. Answer: Two bulges exist because tides come from the difference in the Moon's pull, not the pull itself.