(5) Pressure and Fluids Flashcards
What is meant by a ‘fluid’?
A liquid or gas
In any fluid, at what angle do the forces (due to pressure) act on a a given surface?
At right angles to the surface (normal)
What is the equation for pressure?
Pressure = force / area
How can we calculate the pressure due to a column of liquid?
Pressure = height of column x density of liquid x gravitational field strength
What happens to the pressure in a column of liquid?
In a liquid, pressure at a point increases with the height of the column (above that point). (The pressure is greater at the bottom).
How does pressure in fluids increase with depth?
As the depth increases, the mass of liquid about that depth also increases. This means that the force due to mass increases, 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. This means that the force from the fluid above a certain point is larger. Since the force increases so does the pressure.
Why are objects in a fluid subject to upthrust?
When an object is smudged in a fluid, it has a higher pressure below than it does above, as there is more weight above it at the bottom than there is at the top.
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
Which factors influence whether an object will sink or float?
• upthrust
• weight
• density of fluid
What happens to the density of the atmosphere with increasing altitude?
The atmosphere becomes less dense as the altitude increases
Why does atmospheric pressure change with height?
Pressure is created by collisions of air molecules. The quantity of molecules (and so weight) decreases as the height increases.
Describe what Earths atmosphere is:
A this layer of gas surrounding earth
