It looks like a refractor.
Answer:
Friction force is the force that one object exerts in another when the two rub against each other. Most of the time, friction force opposes the motion of an object.
Explanation:
<span>An isotope is a form of a
chemical element whose atomic nucleus contains a specific number of neutrons in
addition to the number of protons that distinctively defines the element. The
nuclei of most atoms have neutrons as well as protons.</span>