Pressure and pressure differences in fluids 5.5 Flashcards
What is meant by the term ‘fluid’?
A liquid or a gas
In any fluid, at what angle do the forces due to pressure act on a given surface?
At right angles (normal to) the surface
State the equation used to calculate pressure. GIve appropriate units
Pressure= Force/Area
Pressure (Pascals), Force (Newtons), Area (metre²)
What happens to the density of the atmosphere with increasing atmosphere?
The atmosphere becomes less dense as altitude increases
Explain why atmospheric pressure decreases with an increase in height
- Pressure is created by collisions of air molecules
- The quantity of molecules (and so weight) decreases as the height increase
- This means atmospheric pressure decreases with an increase of height
What is the Earth’s atmosphere?
A thin (relative to the magnitude of the Earth) layer of gas surrounding the Earth
How does pressure in fluids increase with depth?
As the depth increase, the mass of liquid above that depth also increases. This means that the force due to the mass increase. Since the force has increased whilst the area has remained constant, the pressure will increase
Why does pressure in fluids increase with density?
As the density of a fluid increases, the number of particles in a given volume increases. Consequently the weight of the fluid is greater. This means that the force from the fluid above a certain point is larger. Since the force has increased, the pressure also increases
What equation shows the magnitude of pressure in liquids at different depths?
Pressure due to a column of liquid (Pa) = Column height (m) x density (kg/m³) x gravitational field strength (N/kg)
P = hpg
Why are objects in a fluid subject to an upthrust?
When an object is submerged in a fluid, it has a higher pressure below it than it does aboe, as there is more weight below it at the bottom than there is at the top. This lead to an upward force called upthrust. You float or sink depending on whether the upthrust is more or less than your weight.
What is upthrust equal to?
The weight of the fluid that the object displaces
What factors influence whether an object will sink or float?
- Upthrust
- Weight
- Density of fluid
Explain why an object with a density greater than that of water can never float
Upthrust is equal to the weight of the displaced fluid. If the density of the object is high, there would not be enough volume displaced to produce an upthrust larger than the object’s weight. This means that it will sink
