The size of a needle of a syringe controls flow rate better than the thumb pressure exerted by a doctor while administering an injection.

Explanation

For a> constant height, the Bernoulli’s theorem is expressed as
p + 12 pυ2 = constant
In this equation, the pressure P occur with a single power whereas the velocity occurs with a square power. Therefore, the velocity has more effect compared to the pressure. It is for this reason that needle of the syringe controls flow rate better than the thumb pressure exerted by the doctor.