Why is a microscope used to observe bacteria? ?

A phase contrast microscope uses an optical technique that works by the use of a device to read the difference in thickness of the subject affecting the phasing of light resulting in a high contrast image. Staining bacteria also help microscope users to see bacterial structures that would have otherwise been invisible to the naked eye.

we need to know the time interval during which the force acts. impulse of force = momentum change

i think it's 35 meters