Because the molecules that move freely begin to compact closer together, with less heat, means less molecular activity.
The second one if it’s on edge
Answer: independent variable: Size of the feather.
Explanation:
In an experiment, the manipulated/independent variable is, as the name implies, the variable that the scientist can control.
In this case, the scientist has only one variable that he can control at will, and this is the size of the feather (he can choose which feather he uses for the experiment)
So the manipulated variable will be the size of the feather.
And the dependent variable is the one that "answers" to the changes in the manipulated variable.
In this case, will be the time that it takes to the feather to fall to the ground.
Atoms diameter are on the order of 60 to 600pm (picometers). This is around 6*10^-11.