Explain what a convection current is?
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Convection currents are flowing fluid that is moving because there is a temperature or density difference within the material.

Because particles within a solid are fixed in place, convection currents are seen only in gases and liquids. A temperature difference leads to an energy transfer from an area of higher energy to one of lower energy.

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.