Question

can pressure be negative ??​

Answer 1

Answer:

1. According to classical physics, no, you cannot have negative absolute pressure because zero absolute pressure refers to a vacuum, which is the absence of any matter. However, you can have negative relative pressure. For example, when using a pump to draw matter uphill it is quite natural to describe the pressure at the top of the apparatus as negative ("suction") relative to the 1 atmosphere pressure at the bottom. However, because of the constraint that the absolute pressure can't be negative, it is impossible to use such a pump to draw water more than about 10 meters upwards—that's the height which the water would reach under an absolute pressure of zero.

2. I don't get it. Why do you think positive gravitational force would lead to an empty planetary core? Since the classical gravitational force is always attractive force, it tends to draw matter closer together, rather than push it apart.