# Fluids - Statics 1

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• Created by: cbd19
• Created on: 04-02-20 19:48
How does pressure work?
When molecules move they have elastic collisions with the wall, energy and momentum are conserved. The wall exerts a force on molecules and they exert equal force back. Pressure is force per unit area.
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Is force perpendicular or parallel to the plane of action?
The direction of the force on a plate is perpendicular to the plane of the plate.
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What are the units of the pascal. How many pascals in a bar and an atmosphere? How about psi?
1 Pa= 1N/m^2 10^5 Pa= 1 bar 1atm= 101325 Pa 1psi= 6894.8 Pa
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What does the continuum approach assume about the direction of forces?
With continuum approach, collisions are averaged so force acts perpendicular to the surface although in reality this doesn't happen.
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How can large pressures and forces be created?
Small forces can produce large pressures if area minimised and small pressure differences over large areas produce large forces, such as wind flows.
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How is pressure transmitted and what applications use this?
Pressure is transmitted through a fluid. Speed of transmission relies on speed of sound in medium and container shape. When tyre is squeezed, pressure rises everywhere. Hydraulic presses use this, with force being increased due to area difference
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What are absolute and gauge pressures?
Absolute pressure - p with respect to vacuum, gauge pressure - pressure relative to atmosphere.
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How does pressure change vertically in water?
Pressure only changes with depth in hydrostatic situations and is constant in horizontal x,y planes. The vertical force balance shows pressure=pressure0+pgz*
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What does p-p0 formula mean?
pressure-pressure at surface = fluid weight per unit area
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How do water towers use pressure?
A single water tower can pressurise a whole system with pressure equal to density of water *g*H (height between tower and taps)
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Are water levels the same in tubes?
Water levels in tubes are same as in reservoir due to hydrostatic pressure distribution. Water level in piezometers is same as reservoir. To find pressure at a certain point in a tube, start from surface and go down to level to find pressure there.
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How can you find pressure on the enclosed side of a partial enclosure?
In a partial enclosure, you can go to the bottom of it to find the pressure, then minus the pressure on the other side of the tube to find pressure on the enclosed side
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Why can we neglect hydrostatic pressure change in gas?
We can neglect hydrostatic pressure change in gas as density of gas much less
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What is a manometer?
Manometer is a u shape and measures pressure differences between two locations in a flow
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## Other cards in this set

### Card 2

#### Front

Is force perpendicular or parallel to the plane of action?

#### Back

The direction of the force on a plate is perpendicular to the plane of the plate.

### Card 3

#### Front

What are the units of the pascal. How many pascals in a bar and an atmosphere? How about psi?

### Card 4

#### Front

What does the continuum approach assume about the direction of forces?

### Card 5

#### Front

How can large pressures and forces be created?