Liquid Pressure: How Does It Exert Pressure?

[Pranav Jha]

how does liquid exert pressure in all directions?
When a liquid is placed in a container, i understand that it exerts pressure on the bottom of the container due to its weight but why does it exert pressure on the sides of the container?
is that due to the fact that the molecules in liquid are free to move in all directions (relatively as compared to a solid)?
this thing is really bugging me and consequently i cannot understand Pascal's law

 

[vlado_skopsko]

Yes, that is because the molecules of the liquid move in all directions.

 

[Pranav Jha]

Yes, that is because the molecules of the liquid move in all directions.

f you release a Ping-Pong ball beneath the surface of water, it will rise to the surface. Would it dothe same if submerged in a big blob of water floating weightless in an orbiting spacecraft ?
A Ping-Pong ball in water in a zero-g environment would experience no buoyant force.
This is because buoyancy depends on a pressure difference on different sides of a submerged
body. IN THE WEIGHTLESS CONDITION NO WATER PRESSURE EXISTS

If water pressure were due to movement of water molecules at microscopic level, shouldn't there be water pressure at zero gravity condition as well?

 

[vlado_skopsko]

If water pressure were due to movement of water molecules at microscopic level, shouldn't there be water pressure at zero gravity condition as well?

There will be pressure due too the molecules motion, but not pressure difference in the liquid, the molecules will be bouncing from the body, equally from all sides, so there wot be a force present, no relative motion.

 

[Pranav Jha]

There will be pressure due too the molecules motion, but not pressure difference in the liquid, the molecules will be bouncing from the body, equally from all sides, so there wot be a force present, no relative motion.

What does "no relative motion" actually mean?
Similarly, how does the absence of gravity guarantee that the molecules bounce equally from all sides giving no net force and thus no net pressure?

 

[vlado_skopsko]

Relative motion is motion of two or more bodies in respect of one and other, two cars on a highway are going in same direction one with 100 km\h and the other with 110 km\h, so there is relative motion between the two cars, with speed of 10 km\h.

If the fluid is liquid then there are intermolecular forces acting, like springs, preventing the liquid to fill all the space available, but the molecules have some kinetic energy, their number is huge, they hit each other constantly, so statistically the probability the body to be hit from each side is the same(no force is suggesting otherwise). There is no pressure difference.
In gravity field (there is force present) the pressure in fluid depends on the depth, because of the weight of the fluid. So there is pressure difference between the upper and lower surface of the body (on the lower surface there is higher pressure) creating force acting upwards, buoyant force.

 

[russ_watters]

Similarly, how does the absence of gravity guarantee that the molecules bounce equally from all sides giving no net force and thus no net pressure?

Absence of gravity ensures they bounce equally on all sides, which results in equal pressure, not no pressure.