Currently Empty: $0.00
4. Density What is Density? Measuring Density (solids & liquids) Floating and Sinking (qualitative)
Year 8 • Physics
Density
This lesson explains what density means, how to measure density of solids and liquids, and why objects float or sink. Real-life examples are used to help you understand density easily.
Lesson Objectives
- Understand what density means.
- Use the density formula correctly.
- Measure density of solids and liquids.
- Explain floating and sinking using density.
- Relate density to real-life situations.
1. What Is Density?
Density tells us how much mass is packed into a certain space.
It explains whether something feels heavy or light for its size.
Think About This:
• A stone and a sponge may be the same size
• The stone feels much heavier
➡️ The stone is more dense
• A stone and a sponge may be the same size
• The stone feels much heavier
➡️ The stone is more dense
Objects with high density have a lot of mass in a small space.
Objects with low density have less mass spread out.
2. Density Formula
Density depends on two things: mass and volume.
Density Formula:
Density = Mass ÷ Volume
Density = Mass ÷ Volume
• Mass is measured in grams (g) or kilograms (kg)
• Volume is measured in cm³ or m³
• Density is measured in g/cm³ or kg/m³
Example:
A toy has a mass of 200 g and a volume of 100 cm³.
Density = 200 ÷ 100 = 2 g/cm³
3. Measuring Density of Solids
To find the density of a solid, we measure its mass and volume.
Regular Solids (cube, brick):
• Measure mass using a balance
• Measure length, width, height
• Volume = length × width × height
• Measure mass using a balance
• Measure length, width, height
• Volume = length × width × height
Irregular Solids (stone, key):
• Measure mass using a balance
• Measure volume using water displacement in a measuring cylinder
Real-life example:
Finding density of a rock found in a garden.
4. Measuring Density of Liquids
Liquids also have density.
Steps:
• Measure volume using a measuring cylinder
• Measure mass of the liquid (subtract container mass)
• Use the density formula
• Measure volume using a measuring cylinder
• Measure mass of the liquid (subtract container mass)
• Use the density formula
Example:
Oil floats on water because oil has lower density than water.
5. Floating and Sinking
Whether something floats or sinks depends on its density compared to the liquid.
• If object density < liquid density → floats
• If object density > liquid density → sinks
• If object density > liquid density → sinks
Real-Life Examples:
• Ships float because their average density is low
• Ice floats on water
• Stones sink in water
• Oil floats on water
• Balloons float in air because they are less dense
Practice Questions
A. Fill in the Blanks
- Density is mass divided by __________.
- Density is measured in __________.
- An object floats if it is __________ dense than water.
- Mass is measured using a __________.
- Ice floats because it has __________ density.
B. True or False
- A sponge is more dense than a stone.
- Oil floats on water.
- Density depends on mass and volume.
- Heavy objects always sink.
- Ships float because of low average density.
C. Short Answer
- Define density.
- Write the density formula.
- Why does a stone sink in water?
- How do you find volume of an irregular solid?
- Give two examples of floating objects.
D. Numerical Problems
- Mass = 300 g, Volume = 150 cm³. Find density.
- Mass = 500 g, Volume = 250 cm³. Find density.
- An object has density 0.8 g/cm³. Will it float in water?
- Find mass if density is 2 g/cm³ and volume is 50 cm³.
- Find volume if mass is 400 g and density is 4 g/cm³.
✅ Show Answer Key
A. Fill in the Blanks
- volume
- g/cm³ or kg/m³
- less
- balance
- lower
B. True or False
- False
- True
- True
- False
- True
C. Short Answer
- Density is mass per unit volume.
- Density = Mass ÷ Volume.
- It is more dense than water.
- Using water displacement.
- Ice, ship (any two).
D. Numerical Problems
- 300 ÷ 150 = 2 g/cm³
- 500 ÷ 250 = 2 g/cm³
- Yes, it will float.
- Mass = 2 × 50 = 100 g
- Volume = 400 ÷ 4 = 100 cm³
© Aviate Learning – Density (Year 8)
🌊 Floating & Sinking Simulator (Density)
Adjust the mass and volume of the object.
The simulator calculates density and shows whether the object floats or sinks in water.
Object Density: 0.80 g/cm³
🟢 FLOATS
The object is less dense than water.