IGCSE 0625 · MECHANICS · 1.4

Density

What density means, how to measure it for regular solids, irregular solids, and liquids, and why things float or sink. It builds on mass and leads to pressure and the particle model.

TOPIC 1.4: DENSITY CAMBRIDGE IGCSE PHYSICS 0625 · PATHWAYS TheLucidSTEM · thelucidstem.com BUILDS ON 1.1 Quantities 1.3 Mass LEADS TO 1.8 Pressure 2.1 Particle model DENSITY OF MATTER 1 · WHAT IS DENSITY Density is the mass packed into each unit of volume. ρ = m / V ρ = density V = volume Units: kg/m³ or g/cm³. Water has a density of 1000 kg/m³. 2 · REGULAR SOLIDS Find the mass on a balance and the volume from the measured dimensions. l h w V = l × w × h, then use ρ = m / V. 3 · IRREGULAR SOLIDS & LIQUIDS Find an awkward volume by displacement. Lower the solid into a full can; the water that overflows has the same volume as the solid. For a liquid, measure its mass, then read its volume in a measuring cylinder. displaced water = object volume 4 · FLOATING & SINKING An object floats if it is less dense than the fluid, and sinks if it is denser. floats sinks Ships float: their average density is low. A hot air balloon rises as the warm air inside it is less dense than the cool air.
TOPIC 1.4: DENSITY CAMBRIDGE IGCSE PHYSICS 0625 · PATHWAYS TheLucidSTEM · thelucidstem.com BUILDS ON 1.1 Quantities 1.3 Mass LEADS TO 1.8 Pressure 2.1 Particle model DENSITY OF MATTER 1 · WHAT IS DENSITY Density is the mass packed into each unit of volume. ρ = m / V ρ = density V = volume Units: kg/m³ or g/cm³. Water has a density of 1000 kg/m³. 2 · REGULAR SOLIDS Find the mass on a balance and the volume from the measured dimensions. l h w V = l × w × h, then use ρ = m / V. 3 · IRREGULAR SOLIDS & LIQUIDS Find an awkward volume by displacement. Lower the solid into a full can; the water that overflows has the same volume as the solid. For a liquid, measure its mass, then read its volume in a measuring cylinder. displaced water = object volume 4 · FLOATING & SINKING An object floats if it is less dense than the fluid, and sinks if it is denser. floats sinks Ships float: their average density is low. A hot air balloon rises as the warm air inside it is less dense than the cool air.
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