Density

Question 1

Density

Answer 1

the mass of an object per unit volume

Question 2

What are the units for density ?

Answer 2

kg / m cubed

Question 3

What are the units of mass ?

Answer 3

kg

Question 4

What are the units of volume ?

Answer 4

m cubed

Question 5

What is the formula for density?

Answer 5

mass / volume = density

Question 6

What is the density of solids ?

Answer 6

• have a high density
• this is because the particles are in fixed positions and can only vibrate on the spot
• there is a lot of mass packed into the volume

Question 7

What is an exception of this case ?

Answer 7

a polystyrene block
this is because although it is a solid it has lots of air spaces so there is less mass packed into the same volume

Question 8

What is the density of a liquid ?

Answer 8

Liquids also tend to have a high density (but lower than solids)
- this is due to the particles also being close together so there is a lot of mass for its volume

Question 9

What is the density of a gas ?

Answer 9

Gases have low densities
- this is because particles are far apart and have lots of space to move so they have low masses for the same volume

Question 10

How can we calculate the volume of a regular object ?

Answer 10

• measure its mass using a mass balance
• measure its dimensions using a ruler and figure out the volume using an equation depending on the object
• for example, if the object is a cube, work out the length of one side and cube it to calculate the volume
• work out density (mass / volume)

Question 11

What is an irregular object ?

Answer 11

One with dimensions not easy to measure

Question 12

Then how do we calculate the volume of an irregular object ?

Answer 12

• fill a eureka can with water until it is level with the bottom of the spout
• place a measuring cylinder under the spout
• put object into eureka can and see amount of water displaced using measurements on measuring cylinder
• this is the object’s volume

Question 13

How do we calculate the density of an irregular object ?

Answer 13

• measure mass using a mass balance
• find volume using method above
• density = mass / volume

Question 14

A rock has a mass of 0.6 kg and a volume of 0.15 m cubed.
Calculate its density.

Answer 14

4 kg / m cubed

Question 15

A cube box has a density of 25 kg / m cubed and and a mass of 8kg.
Work out the length of each side of the box.

Answer 15

8 / 25 = 0.32 m cubed
take third root of 0.32 as it is a cube which has all equal sides
= 0.68 m