Does the bubbling that occurs when the methanol is added to the dry sand indicate that the sand and methanol are reacting

It's in the last paragraph of this website.

https://community.ptc.com/t5/PTC-Mathcad/AP-Chemistry-Problem-Help/td-p/64410

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.

8 m/s because for him to get the same amount of energy as ray is putting out, bobby, who weighs half as much as ray, needs to run twice as fast.