You are explaining to a friend that physics tells us that a rolling ball that is not slipping has zero
work being done on the ball by friction. Your friend asks you, “Doesn't this mean that the ball will
roll forever in a vacuum? That can't be right!" How do you answer your fiend? How do you explain
to your friend that real non-idealized balls actually do lose energy to friction despite not slipping?

it is given that trillions of microbes make up to 1% to 3% of the body mass.

let's take average of this percentage: 2%

consider the average mass of the human body as 70 kg.

then, trillions of microbes would have mass  

therefore, 100 trillion micro-organisms would weigh:

this is an approximate value and could change depending on the mass of the human body and percentage of the microbes present in it.

average mass per microorganism =

answer(20) psi;