P11 force and pressure

Question 1

What causes pressure

Answer 1

When objects exert forces on each other or when a fluid exerts a force on an object in contact with the fluid

Question 2

Definition of pressure

Answer 2

Pressure is the force per unit area

Question 3

Pressure, area and force equation

Answer 3

P = F/A
Pressure = Force / Area

Question 4

Units in force equation

Answer 4

Pressure = pascals (Pa / N/m^2)
Force = newtons (N)
Area = metres squared (m^2)

Question 5

Relationship between pressure and depth

Answer 5

Pressure increases with depth because pressure = density x gravity x height and gravity and density are fixed in a liquid so height is the only thing to effect it

Question 6

Pressure equation involving density

Answer 6

P = Pgh
Pressure = density x gravity x height

Question 7

How do you measure height in a liquid

Answer 7

Surface of water to point

Question 8

What is a barometer

Answer 8

Measures pressure, made by filling a tube with mercury and then inverting it into a bowl of mercury. The mercury falls until the weight of the mercury is supported by the air pressure on the surface

Question 9

What is a manometer

Answer 9

U shaped tube filled with liquid connected to a gas supply. The change in height of the liquid is the gas pressure

Question 10

What is the earth’s atmosphere and atmospheric pressure

Answer 10

Layer of air around the Earth. Exerts 100 kPa every square metre

Question 11

What is atmospheric pressure caused by

Answer 11

Air molecules colliding with objects, each collision exerts a tiny force and millions happen a second

Question 12

Relationship between pressure and altitude

Answer 12

As altitude increases, pressure decreases because the weight of air particles above decreases as altitude increases therefore there are less particles so less collisions

Question 13

How do suction caps work

Answer 13

The action of squeezing the suction onto the wall pushes out air particles meaning the pressure inside the cap is less than the atmospheric pressure so it stays on the wall as the resultant force acts towards the wall

Question 14

What is upthrust

Answer 14

Upwards acting force that a liquid exerts on an object

Question 15

Upthrust and water displacement

Answer 15

If an object is submerged in liquid, it displaces the liquid. When the object is fully submerged, the volume of water displaced equals the volume of liquid displaced

Question 16

Is upthrust bigger at the top or bottom of objects

Answer 16

Bottom as the pressure is higher

Question 17

Relationship between upthrust and weight of fluid displaced

Answer 17

They are equal

Question 18

Why do objects sink

Answer 18

If the upthrust is less than the weight of an object, it will sink

Question 19

Why do objects float

Answer 19

If the upthrust is equal to the weight of an object, it will float

Question 20

What happens if upthrust is larger than the objects weight

Answer 20

It will rise up through the water until it reaches the surface. If part of the object protrude out from the surface then less volume is submerged, displacing the water, hence the upthrust force decreases until it balances the weight of the object