Density Basics
What is the formula for density?
Density = Mass ÷ Volume
Why does ice float on water?
Ice is less dense than liquid water.
Why do solids have a fixed shape?
Because their particles are tightly packed and held by strong forces.
Why can liquids flow but solids cannot?
Liquid particles can slide past each other while solid particles cannot move
How do you find the density of a regular object like a cube or a cuboid?
Measure its mass and calculate its volume using length × width × height, then use density = mass ÷ volume.
What is the unit of density?
kg/m³ or g/cm³
Why do hot air balloons rise?
Heated air inside the balloon is less dense than surrounding air.
What happens to solid particles when they are heated?
They vibrate faster but stay in fixed positions.
Why do gases fill the entire container they are in?
Because gas particles move freely and spread out to fill all available space.
How can you find the volume of an irregular object like a stone?
By water displacement — submerge the object in a measuring cylinder and record how much the water level rises.
Which has a higher density: stone or air?
Stone
Why does oil float on top of water?
Because oil has a lower density than water.
Why do solids usually have a higher density than liquids?
Their particles are closer together, giving more mass per volume.
What happens to gas density when temperature increases?
It decreases because particles move farther apart.
A metal cube has a mass of 80 g and sides of 2 cm. What is its density?
Volume = 2 × 2 × 2 = 8 cm³ → Density = 80 ÷ 8 = 10 g/cm³.
If an object has a mass of 200 g and a volume of 50 cm³, what is its density?
4 g/cm³
Why does hot air rise in the atmosphere?
Because heated air becomes less dense than the surrounding cooler air.
Give an example of a dense solid used in construction.
Iron or concrete.
Why does perfume smell spread across a room?
Gas particles diffuse and move freely in all directions.
A stone raises the water level in a measuring cylinder from 50 mL to 70 mL and has a mass of 40 g. What is its density?
Volume = 70 – 50 = 20 cm³ → Density = 40 ÷ 20 = 2 g/cm³.
A cube of metal has sides of 2 cm and mass of 32 g. Find its density.
4 g/cm³
Why do scuba divers wear weighted belts?
To increase their density and help them sink in water.
Why does a metal cube feel heavier than a wooden cube of the same size?
Why does a metal cube feel heavier than a wooden cube of the same size?
Because metal has a higher density than wood.
Why does water take the shape of its container?
Because liquid particles can move and flow to fit the shape of the container.
Why do we use the water displacement method for irregular objects?
Because their shapes make it difficult to calculate volume using standard formulas.