What motion produces two high tides in a day?

Explanation

**Step-by-Step Solution:**

1. **Understanding Tides**: Tides are the rise and fall of sea levels caused by the gravitational forces exerted by the moon and the sun on the Earth.

2. **Gravitational Pull of the Moon**: The moon exerts a gravitational pull on the Earth. This pull affects the water in the oceans, causing it to bulge out on the side of the Earth that faces the moon. This bulge is what we refer to as a high tide.

3. **Centrifugal Force**: As the Earth rotates, there is also a centrifugal force acting on the water. This force is due to the rotation of the Earth and causes water to bulge out on the opposite side of the Earth from the moon.

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