Required practical - Investigating density Revision Notes for AQA GCSE Physics Combined Science

Required practical - Investigating density

This practical helps you learn how to measure the density of different solids and liquids safely and accurately. Density is a fundamental property that describes how much mass is contained in a given volume of material.

What is the aim?

The main goal is to work out the density of solids and liquids by measuring their mass and volume. You'll use the fundamental formula:

$\text{density} = \frac{\text{mass}}{\text{volume}}$

Equipment you need

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Essential Equipment List

Electronic balance (to measure mass)
Measuring cylinder
Displacement can (for irregular solids)
Ruler (for regular solids)
Various solid objects and liquids to test

Method for measuring solid density

Step 1: Use an electronic balance to find the mass of your solid object. Write this down in grammes.

Step 2: Find the volume. You have two options:

Regular shapes: Measure length, width and height with a ruler, then calculate volume
Irregular shapes: Fill a displacement can with water. Put your object in and collect the overflow water in a measuring cylinder. The volume of water displaced equals the volume of your object.

Step 3: Record your volume measurement in cm³.

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The displacement method works because when an object is submerged in water, it pushes away (displaces) a volume of water equal to its own volume. This is known as Archimedes' principle.

Method for measuring liquid density

Step 1: Put an empty measuring cylinder on the electronic balance and set the reading to zero.

Step 2: Pour your liquid into the measuring cylinder up to a clear marking.

Step 3: Read the mass of the liquid from the balance (in grammes) and the volume from the cylinder (in cm³).

Taking accurate measurements

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Avoiding parallax error: When reading the measuring cylinder, make sure your eye is level with the meniscus (the curved surface of the liquid). If you read from above or below, your measurement will be wrong.

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Zeroing equipment: Always reset your electronic balance to zero before each measurement to ensure accuracy.

Recording your results

Set up a table with these headings:

Material
Mass (in g)
Volume (in cm³)
Density (in g/cm³)

Calculate density using: $\text{density} = \frac{\text{mass}}{\text{volume}}$

Converting between units

Density can be measured in different units:

g/cm³ (grammes per cubic centimetre)
kg/m³ (kilogrammes per cubic metre)

To convert:

From g/cm³ to kg/m³: multiply by 1000
From kg/m³ to g/cm³: divide by 1000

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Unit Conversion Example

Water has a density of 1 g/cm³. To convert this to kg/m³:

1 g/cm³ × 1000 = 1000 kg/m³

This means water has the same numerical density value, but the units change by a factor of 1000.

Safety considerations

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Safety Warning: Be careful when choosing materials to test. Some substances like mercury are dangerous and should not be used in school experiments. Always check with your teacher before testing unknown substances.

Worked example

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Worked Example: Calculating Liquid Density

A measuring cylinder contains 256 cm³ of liquid with a mass of 454 g.

Step 1: Identify the known values

Mass = 454 g
Volume = 256 cm³

Step 2: Apply the density formula $\text{density} = \frac{\text{mass}}{\text{volume}} = \frac{454 \text{ g}}{256 \text{ cm³}} = 1.77 \text{ g/cm³}$

Answer: The density of the liquid is 1.77 g/cm³

Why accuracy matters

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Small errors in measuring mass or volume can lead to big errors in your final density calculation. This is because density is calculated by dividing two measured quantities, so any errors get magnified in the final result.

This is why it's essential to:

Read measurements carefully
Avoid parallax errors
Use precise equipment
Take multiple readings where possible

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Key Points to Remember:

$\text{density} = \frac{\text{mass}}{\text{volume}}$ - this is the fundamental formula you must know
Use an electronic balance for accurate mass measurements
Read the meniscus at eye level to avoid parallax errors when measuring volumes
Different methods work for different objects - regular solids can be measured directly, irregular solids need displacement
Units matter - know how to convert between g/cm³ and kg/m³ by multiplying or dividing by 1000
Safety first - always check materials are safe to use before testing

Required practical - Investigating density (AQA GCSE Physics Combined Science): Revision Notes