05 Pressure and Density

Question 1

Define density

Answer 1

the mass per unit volume

Question 2

How do you measure volume accurately when using a measuring cylinder?

Answer 2

Read the volume at eye level and to the bottom of the meniscus

place measuring cylinder on a level surface

Question 3

What is the unit for density?

Answer 3

g/cm³ or kg/m³

Question 4

Which orientation of the block below would create in a smaller pressure on a table?

Answer 4

First orientation

P = F/A

The second block has a larger area in contact with the table, for the same force, therefore, the pressure is lower

Question 5

How can the volume of an irregular object be found using a measuring cylinder?

Answer 5

1. Half fill measuring cylinder with water and read initial volume at eye level and bottom of the meniscus
2. lower object into measuring cylinder- make sure that it is fully submerged and water level has not risen above the scale
3. read final volume at eye level and bottom of the meniscus
4. Volume of object = final volume - initial volume

Question 6

The second object has half the mass but the same volume, How does its density compare to the first object?

Answer 6

density = mass / volume

if mass is double for the same volume, the density doubles.

density is proportional to mass

Question 7

How could you find the density of a paperclip accurately?

Answer 7

1. measure the mass of 50 paperclips on a balance
2. half fill a measuring cylinder with water and record initial volume
3. carefully add 50 paperclips and record final volume.
4. calculate the volume by taking the difference
5. Find density = mass / volume

Question 8

What is a pascal?

Answer 8

1 Pascal = 1 Newton per metre square

Question 9

How do you find the density from a mass vs volume graph?

Answer 9

calculate the gradient

gradient = rise/run = mass/volume

Question 10

Explain what design feature makes a knife able to cut easily.

Answer 10

A sharp knife with a small surface area creates a greater pressure for the same force.

pressure = force/area

The knife will cut more easily

Question 11

What equation links density, mass and volume?

Answer 11

Question 12

What is the unit for force?

Answer 12

Newton or N

Question 13

Camels have adapted to walk effortlessly in the desert sand. Explain

Answer 13

Camels feet have a large surface area

P = F/A

A larger surface area for the same force results in lower pressure

The camel will not sink as much in the sand and can walk more easily.

Question 14

How can the volume of an irregular object be measured accurately using a Eureka can?

Answer 14

1. overfill eureka can with water and wait for water to stop dripping from the spout
2. hang object from a string and slowly lower the object into the water
3. make sure that the object is fully submerged

Question 15

Which orientation of the block below would create a larger pressure on a table?

Answer 15

Second orientation

P = F/A

The second block has a smaller area in contact with the table for the same force, therefore, the pressure is higher

Question 16

What is the unit for volume?

Answer 16

m³

Question 17

If a block of wood is cut in half, how does the density of the original block compare with the new half blocks?

Answer 17

Their densities are the same.

Both the mass and the volume were halved.

Question 18

Which dam must withstand a larger pressure?

Answer 18

The dam on the right. It has a greater depth (h) and so the pressure on the dam will be greater.

Static liquid pressure does not depend on the volume of the liquid - but its depth.

Question 19

What is the unit for pressure?

Answer 19

Pascal (Pa)

Question 20

What is the equation that links pressure, density of a fluid, gravity and depth?

Answer 20

Question 21

Which section A, B, C, D or E experiences the largest pressure?

Answer 21

P = density x gravity x depth

All the sesctions experience the same pressure since the depth of water is the same.

Pressure at depth is not affected by the volume of water- only the depth of water above it.

Question 22

How does the density vary between ice and sea water?

Answer 22

Ice has less particles per unit volume

ice has a lower density

Ice floats on sea water

Question 23

How can mass be measured accurately?

Answer 23

• placed balance on level surface
• tare (zero) balance before use

Question 24

How does the pressure vary with depth in the ocean?

Answer 24

As depth double, pressure doubles.

Pressure is proportional to depth

The graph is a straight line through the origin.

Question 25

What is the unit for mass?

Answer 25

kg

always convert grams to kilograms

Question 26

Fluid pressure acts in all directions.

What causes air pressure?

Answer 26

Air particles move in all directions and collide with objects

Air particles move fast and freely

Air pressure is related to the depth of air over the object.

Question 27

What is the unit for area?

Answer 27

m² or cm²

Question 28

What equation links pressure, force and area?

Answer 28

Question 29

Which object (a or b) has the largest density?

Answer 29

Object a

It has more mass per unit volume - the gradient is steeper

Question 30

Which object below would have the highest density values?

Answer 30

First object

Greater mass per unit volume

The particles are more closely packed