Pressure and pressure differences in fluids (5.5) (M)

Question 1

What can a fluid be?

Answer 1

either a liquid or a gas

Question 2

What does the pressure in fluids cause?

Answer 2

a force normal (at right angles/perpendicular) to any surface

Question 3

Why does the pressure of a liquid increase with depth?

Answer 3

Because as depth increases, there is a greater volume of water above a person,

Question 4

Why does the pressure of a liquid increase with density?

Answer 4

As density increases, there is greater weight acting downwards

Question 5

Why are the walls of a dam thicker at the bottom?

Answer 5

There is a greater pressure of liquid at the bottom, as the depth is greater, and therefore there is a greater weight of liquid acting downwards

Question 6

Why does a partially (or totally) submerged object rise and float?

Answer 6

The object experiences a greater pressure on the bottom surface than on the top surface

This creates a resultant force upwards

This force is called the upthrust

Question 7

When can an object float?

Answer 7

When the upthrust force equals the object’s weight

Question 8

When does an object sink?

Answer 8

When the upthrust force is less than the object’s weight

Question 9

Describe the relationship between upthrust and weight of water displaced

Answer 9

The size of the upthrust acting on the object is the same as the weight of water displaced by the object

so it can float

Question 10

Why does an object with a greater density than water sink?

Answer 10

The object cannot displace a volume of water equal to its own weight

So weight of the object is greater than the upthrust and so the object sinks

Question 11

Describe the observation for an object with the same density as water floating?

Answer 11

The surface of the object is at the surface of the water

this will have to displace more water than an object with a lower density

Question 12

How does a greater surface area affect whether an object can float?

Answer 12

there is more surface area to distribute the weight across and displace the water, so it will float

Question 13

What is the atmosphere?

Answer 13

a thin layer (relative to the size of the Earth) of air round the Earth

Question 14

The atmosphere gets (…) dense with increasing altitude

Answer 14

less

Question 15

How is atmospheric pressure created?

Answer 15

Air molecules colliding with a surface

Question 16

important to learn

Why does atmospheric pressure decrease with an increase in height?

Answer 16

Air molecules colliding with a surface creates pressure

At increasing altitude distance between molecules decrease or at increasing altitude, there are fewer molecules (above a surface)

so the number of collisions with a surface decreases or so always less weight of air than blow (the surface)

Question 17

Why must aircraft that fly at high altitudes be pressurised?

Answer 17

If the air pressure is too low, humans cannot take in oxygen quickly enough to meet their bodies’ needs

Question 18

2 needed

What are the factor that influence floating and sinking?

Answer 18

• density
• surface area

Question 19

Other than weight, what other force may act downwards on an object?

Answer 19

drag

Question 20

Why does water sometimes exert upthrust on an object?

Answer 20

Pressure acting on the bottom of the object greater than the pressure acting on top

Question 21

A hole is made in a bottle of water, explain why, as the volume of the water decreases, the jet of water coming from the hole travels a shorter distance?

Answer 21

The pressure at the hole decreases

So the water exits at a lower speed

Question 22

Why the further a swimmer dives below the surface of a swimmer, the greater the pressure on the swimmer?

Answer 22

Increasing depth increases the volume of water above the swimmer, so increases the weight acting on the swimmer

Question 23

Velocity is (…) in shallow water

Answer 23

slower

and converse

Question 24

What can be concluded from this model about pressure in a liquid?

Answer 24

Pressure (in a liquid) acts in all directions

Question 25

What property of liquids means that it is ideal for a hydraulic brakes system?

Answer 25

Liquids are (virtually) incompressible