P10 Pressure In Liquids And Gases

Question 1

What is a fluid?

Answer 1

A subject that can flow.

Both liquid and gasses can be fluids.

Question 2

When particles of a fluid collide with a surface, how do they exert a force?

Answer 2

At a right angle (normal) to the surface.

Question 3

What is the definition of pressure?

Answer 3

The force acting per square metre on a surface.

Question 4

What is the unit of pressure ?

Answer 4

A pascal (Pa)

Which is equal to one newton per square metre.

Question 5

What is the calculation for pressure?

Answer 5

Pressure (Pa) = force (N) ÷ area (m^2)

P = F ÷ A

Question 6

What calculation can you use to calculate the pressure caused by a column of liquid?

Answer 6

Pressure (Pa) = height of the column (m) X density of the liquid (kg/m^3) gravitational field strength (N/kg)

P = h p g

Question 7

How do you calculate the difference in pressure at different depths in a liquid?

Answer 7

Calculate the pressure at each depth (h) and subtract the smaller value from the larger one.

Question 8

What is the definition of upthrust?

Answer 8

An object that is full or completely submerged in a fluid experiences a greater pressure on its bottom surface than its top surface, the difference in pressure creates an upwards resultant force on the submerged object, know as upthrust.

Question 9

When will an object sink?

Answer 9

When the weight is greater than the upthrust.

Question 10

When will an object float?

Answer 10

When it’s weight is equal to the upthrust.

Question 11

Whether an object in a fluid will float or sink depends on its density because (3):

Answer 11

1) the upthrust on an object is equal to the weight of the fluid it displaces

2) an object that is more dense than the fluid will sink because it’s weight is greater than the weight of the liquid displaced (and so greater than the upthrust)

3) an object that is less dense than the fluid will float because it’s weight is less than the weight of the fluid displaced (and so less than the upthrust)

Question 12

What is the meaning of ‘displaced’?

Answer 12

Pushes out of the way.

Question 13

What is the thin layer of air that surrounds the earth known as?

Answer 13

The atmosphere.

Question 14

Air is fluid, so what is the pressure in the atmosphere called?

Answer 14

Atmospheric pressure.

Question 15

What is atmospheric pressure caused by?

Answer 15

Air molecules colliding with surfaces.

Question 16

Atmospheric pressure decreases the higher above surface you are because (2):

Answer 16

1) there are fewer air molecules in total above the surface as the height increases, so the weight of air above the surface decreases

2) density of the atmosphere decreases with altitude, so there are fewer air molecules per cubic metre.