Study Notes
Density is the measure of mass per unit volume of a material. It helps determine whether objects will float or sink in a fluid based on their density relative to the fluid.
- Density — the mass per unit volume of a material. Example: A block of wood with a mass of 200 g and a volume of 400 cm³ has a density of 0.5 g/cm³.
- Upthrust — an upward force exerted by a fluid on a submerged object. Example: A life jacket keeps a person afloat because the upthrust from the water is greater than the weight of the person.
- Buoyancy — the ability of an object to float in a fluid. Example: Ships float because their overall density is less than that of water.
- Equation of Density — Density = Mass / Volume (ρ = m/V). Example: If a liquid has a mass of 50 g and a volume of 100 cm³, its density is 0.5 g/cm³.
Exam Tips
Key Definitions to Remember
- Density: the mass per unit volume of a material.
- Upthrust: an upward force exerted by a fluid on a submerged object.
- Buoyancy: the ability of an object to float in a fluid.
Common Confusions
- Confusing mass with density.
- Assuming all objects with high mass will sink.
Typical Exam Questions
- How do you calculate the density of a liquid? Use the formula ρ = m/V, where m is mass and V is volume.
- What determines if an object will float or sink? An object will float if its density is less than the fluid's density.
- How can you find the volume of an irregularly shaped solid? Use water displacement in a measuring cylinder or eureka can.
What Examiners Usually Test
- Ability to use the density formula correctly.
- Understanding of how density affects buoyancy.
- Methods to determine the density of various materials.