P11 Forces and Pressure

Question 1

what do particles in a gas and liquid exert on the walls of a container?

Answer 1

a force right angles to the walls of the container

Question 2

what is a fluid?

Answer 2

gases and liquids

Question 3

What is the formula for pressure?

Answer 3

P = F/A

Question 4

What is the unit for pressure?

Answer 4

Pascal (Pa)

Question 5

What is the atmosphere?

Answer 5

a thin layer of air around the earth

Question 6

where is the atmosphere most dense?

Answer 6

at the surface of the earth as there are the most number of air particles

Question 7

what happens to the atmosphere as altitude increases?

Answer 7

the atmosphere gets less dense

Question 8

what is the pressure of the atmosphere caused by?

Answer 8

air particles colliding with a surface

Question 9

why does atmospheric pressure decrease with height?

Answer 9

the number of air particles decreases above the surface

Question 10

What increases the pressure of a column of liquid?

Answer 10

height
density of the liquid
gravitational field strength

Question 11

why does an increase in the depth/height of a column of liquid increase the pressure?

Answer 11

there is a greater weight of liquid acting downwards

Question 12

why does increasing density of a liquid increase the pressure?

Answer 12

they have a greater weight acting downwards

Question 13

what is upthrust?

Answer 13

a resultant force acting upwards on an object due to the pressure difference at the top and bottom of the liquid

Question 14

when does an object float?

Answer 14

when the upthrust of the object is greater than or equal to the weight

Question 15

when does an object sink?

Answer 15

when the weight is greater than the upthrust

Question 16

what links the upthrust exerted on an object and the amount of water it displaces?

Answer 16

the weight of the displaced water is equal to the upthrust acting on it

Question 17

why can an object float in terms of the weight of water it displaces and upthrust?

Answer 17

if an object can displace its own weight of water, then the upthrust equals the object’s weight and it will float

Question 18

why do low density objects float high in the water?

Answer 18

the object only has to displace a small amount of water before the displaced water’s weight equals the weight of the object.

Question 19

what does an object float like if it has the same density as water?

Answer 19

the top surface of the object is at the surface of the water

Question 20

why does an object sink?

Answer 20

the object cannot displace a volume of water equal to its own weight so the upthrust is less than the weight of the object so it sinks

Question 21

what is pressure?

Answer 21

force per unit area

Question 22

how do fluids exert pressure?

Answer 22

particles constantly collide with the surface of a container which exerts a force on the area of the surface