Density
Understanding Density
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Density is a measure of mass per unit volume of a material or substance.
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The formula to calculate density is density = mass/volume where mass is measured in kilograms (kg) and volume in cubic meters (m³)
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In practical terms, density tells us how ‘packed’ the particles in a substance are.
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A substance with high density will have particles that are tightly packed, while a substance with low density will have particles that are more spaced out.
Investigating Density
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It’s important to note that you can measure the density of a regular object by measuring its mass and its dimensions and then using the formula density=mass/volume.
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For irregular shaped objects, you find the volume by displacement. This involves dropping the object into a known volume of water and measuring the amount of water displaced by the object.
Factors That Can Affect Density
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Temperature: As temperature increases, most substances expand causing the density to decrease. Conversely, when temperature decreases, substances contract, which increases their density.
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Pressure: If you compress a substance, it becomes denser because you are decreasing its volume.
Density, States and Changes of State
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The state of a substance (solid, liquid, or gas) will affect its density because it influences how closely its particles are packed.
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Generally, solids are denser than liquids, and liquids are denser than gases. For example, ice (solid water) is less dense than liquid water, which is why ice floats on water.
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When a substance changes state, its density will change because the volume changes.
Density and Buoyancy
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Objects float in liquids and gases if their density is less than the density of the liquid or gas.
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If an object has a greater density than the liquid or gas, it will sink. This is known as buoyancy principle.
Understanding Relative Density
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The relative density (or specific gravity) of a substance is the ratio of the density of the substance to the density of a reference substance. It is a dimensionless quantity.
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Usually, water is used as the reference substance for liquids and solids, and air is used for gases.
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For example, if a substance has a relative density greater than 1, it means it’s denser than the reference substance.
Remember to practise problems related to density as density is a very practical aspect of Physics and it is likely that you’ll encounter problem-solving questions relating to this topic.