I'm having a hard time understanding this. I understand that pressure results from molecules colliding into a hypothetical object; the force is equal to the change in momentum of the molecules divided by the time of the collision. I am having a hard time relating this to the idea that the pressure above a point a liquid is equal to pgy. Don't the molecules below a point assert a force against a hypothetical project at that pint; why do we only consider y, the amount of water above a point? Also, how does the force of gravity relate to the force of molecular collisions?
Relating the collision model of pressure to pgy
- Thread starter nm825
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You only consider the water above a point because the pressure exerted by the water on the object cancels out on either the left or the right side of the object. (Think of a cube, the left and the right side are at the same elevation in the water, therefore the pressures are equal and opposite). This is a medium specific property
The pressure below an object relates to it's buoyancy in the water. This is an object specific property.
As far as I know the force of gravity does not change the force of molecular collisions unless you're travelling between planets. Since g is less on the moon than earth, Fg will be less and as a result, the collisions between molecules due to gravity will occur with less force.
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