5.5 - pressure

Question 1

What is meant by the term ‘fluid’?

Answer 1

liquid or gas

Question 2

In any fluid, at what angle do the forces
due to pressure act on a given surface?

Answer 2

At right angles (normal to) the surface

Question 3

What happens to the density of the
atmosphere with increasing altitude?

Answer 3

The atmosphere becomes less dense

Question 4

Explain why atmospheric pressure
decreases with an increase in height.

Answer 4

● Pressure is created by collisions of air
molecules
● The quantity of molecules (and so weight)
decreases as the height increases
● This means atmospheric pressure decreases
with an increase of height

Question 5

What is the Earth’s atmosphere?

Answer 5

A thin layer of gas surrounding the
Earth.

Question 6

How does pressure in fluids increase with depth?

Answer 6

• mass of liquid
  above increases.
• force due to the mass increases
• area
  has remained constant, the pressure will increase.

Question 7

Why does pressure in fluids increase
with density?

Answer 7

• number of
  particles in a given volume increases
• so the weight of fluid is larger
• so force from fluid has increased so pressure also increases

Question 8

Why are objects in a fluid subject to an
upthrust?

Answer 8

• it has a
  higher pressure below it than it does above
• as there is more weight above it at the bottom then the top
• this leads to an upwards force

Question 9

why do people float

Answer 9

upthrust is more than your weight

Question 10

What is upthrust always equal to?

Answer 10

The weight of the fluid that the object
displaces.

Question 11

What factors influence whether an object
will sink or float?

Answer 11

● Upthrust
● Weight
● Density of fluid

Question 12

Explain why an object with a density greater than
that of water can never float

Answer 12

Upthrust is equal to the weight of the displaced fluid
if the density of the object is higher than there wouldnt be enough volume displaced to produce an upthrust larger than the objects weight