Answer:
Following questions are better answered by observational study:
- How does the daytime temperature affect the formation of dew at night?
- How effective is a new toothpaste in reducing cavities?
Following questions are better answered by controlled experiment:
- Which is a better absorber of heat, an object painted black or the same object painted white?
- Why does a rolling ball slow down as it moves?
- Can plants prepare food even in artificial light?
Explanation:
An observational study is one in which the researcher doesn't manipulate anything.
In a controlled experiment, the researcher manipulate the outcome of the experiment and controls the factors that might affect the experiment to see different results in different conditions.
So, for questions over which research do not have any control, mostly natural processes, observational study is a better option.
However, to check why a rolling ball slow down, controlled experiments are done to find out all the factors.
Plants placed in artificial light is also an controlled experiment as the researcher will himself place the plants in artificial light and keep them away from natural light.
Similarly, to check if color of the object affects the amount of heat absorbed by that object, a controlled experiment must be performed. Same object should be painted white and observed and then painted black and observed.
