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For this week's conceptual question, I chose question 19:When there is a global heating trend on Earth, the atmosphere expands and the length of the day increases very slightly. Explain why the length of a day increases.

When there is a global heating trend, Earth's atmosphere expands due to the increase in temperature. Because of the warmer air, the molecules move around more and therefore take up more space. This expansion causes a change in the way that Earth's mass is dispersed, and therefore impacts Earth's movement. There are other forces at play when considering the rotation of Earth such as gravity within the system (the sun, moon and other planets). Since Earth has a rotational movement (rotating around a fixed axis), the principle of the conservation of angular momentum applies.

The principle of the conservation of angular momentum states that the total angular moment of an isolated system will be constant unless there is an external torque acting upon it. Therefore, in this scenario, when the atmosphere of Earth expands, the volume also increases, which changes the distance that Earth must travel for one revolution. If the volume increases, then the speed would decrease because the Earth would have to travel further for one rotation.

With all of this in mind, since Earth would have a further distance (slightly) to travel because of the expanded atmosphere, then the speed of Earth's rotation would be slightly slower and therefore, the day would be slightly longer.