11.2 Density
2 min read•june 18, 2024
is a key property that describes how much is packed into a given . It's calculated by dividing mass by volume and helps explain why some objects float while others sink.
Understanding density is crucial for grasping and ###'_Principle_0###. These concepts explain why ships float, hot air balloons rise, and how we can measure the volume of irregularly shaped objects.
Density
Definition of density
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- Physical property describing mass per unit volume of a substance
- Mathematically defined as mass divided by volume: , where is density, is mass, and is volume
- Higher mass for a given volume results in higher density (lead vs. aluminum)
- Larger volume for a given mass results in lower density (styrofoam vs. steel)
- , independent of size or amount of substance (small vs. large piece of gold)
Density calculations
- Calculate mass by multiplying density and volume:
- Substance with density 2.5 and volume 10 cm³ has mass:
- Calculate volume by dividing mass by density:
- Substance with mass 50 g and density 5 g/cm³ has volume:
Density comparisons and buoyancy
- Different materials have different densities due to atomic structures and compositions
- Gases generally have lower densities than liquids, which have lower densities than solids
- Among solids, metals tend to have higher densities than wood or plastic (steel vs. balsa wood)
- Density determines whether an object floats or sinks in a fluid (buoyancy)
- Object floats if its density is less than the fluid's density (wood in water)
- Object sinks if its density is greater than the fluid's density (rock in water)
- Archimedes' principle: buoyant force equals weight of displaced fluid
- Buoyant force acts upward, opposing gravity
- Object floats if buoyant force exceeds object's weight (ice in water)
- Object sinks if buoyant force is less than object's weight (marble in water)
- can be used to determine an object's volume and, consequently, its density
Density measurement techniques
- : ratio of a substance's density to a reference substance (usually water)
- : device used to measure density of liquids by comparing masses of equal volumes
- : instrument that measures density of liquids by floating in the fluid and measuring displacement
Key Terms to Review (17)
Archimedes: Archimedes was an ancient Greek mathematician, physicist, engineer, and inventor who lived in the 3rd century BC. He is best known for his contributions to the understanding of fluids and density, which are central to the topics of 11.1 What Is a Fluid? and 11.2 Density.
Archimedes’ principle: Archimedes’ principle states that a body immersed in a fluid experiences a buoyant force equal to the weight of the fluid displaced by the body. This principle explains why objects float or sink.
Archimedes' Principle: Archimedes' Principle states that the buoyant force exerted on an object immersed in a fluid is equal to the weight of the fluid displaced by the object. This principle has important applications in understanding the behavior of objects in fluids, including density, pressure, and convection.
Atomic mass: Atomic mass is the weighted average mass of an atom's naturally occurring isotopes, measured in atomic mass units (amu). It reflects both the mass and relative abundance of each isotope.
Buoyancy: Buoyancy is the upward force exerted by a fluid on an object immersed in it, which counteracts the object's weight and allows it to float or be suspended within the fluid. This concept is fundamental in understanding the behavior of objects in fluids and is closely related to the properties of fluids, density, pressure, and fluid dynamics.
Critical density: Critical density is the theoretical density of matter needed for the universe to have a flat geometry. It determines whether the universe will expand forever, collapse back on itself, or reach a stable size.
Density: Density is a fundamental physical property that describes the mass per unit volume of a substance. It is a crucial concept in understanding the behavior of fluids and the principles governing various physical phenomena related to pressure, buoyancy, and fluid flow.
Fluid Displacement: Fluid displacement is the physical phenomenon where an object immersed in a fluid experiences an upward buoyant force equal to the weight of the fluid displaced by the object. This principle is fundamental to understanding concepts like density and Archimedes' Principle.
G/cm³: g/cm³ is a unit of density, which is a measure of the mass of a substance per unit volume. It is commonly used to express the density of solids, liquids, and gases, and is an important concept in the study of physics, particularly in the topic of 11.2 Density.
Hydrometer: A hydrometer is a device used to measure the specific gravity or density of a liquid. It is commonly employed in various applications, such as determining the alcohol content in beverages, monitoring the concentration of solutions, and assessing the state of charge in lead-acid batteries.
The hydrometer operates on the principle of buoyancy, where the depth to which the instrument sinks in a liquid is inversely proportional to the density of the liquid. By observing the depth of submersion and the corresponding scale readings, the specific gravity or density of the liquid can be accurately determined.
Intensive Property: An intensive property is a physical or chemical property of a material that does not depend on the amount or size of the sample being measured. It is a characteristic of the material itself, rather than the quantity of the material.
Kg/m³: kg/m³ is a unit of measurement that represents the density of a substance. It is the mass of a substance per unit volume, specifically kilograms per cubic meter. This unit is commonly used to quantify the density of various materials, including solids, liquids, and gases, in the context of physics and engineering applications.
Mass: Mass is a fundamental property of matter that represents the amount of material in an object. It is a measure of the object's resistance to changes in its motion, and it is a scalar quantity, meaning it has magnitude but no direction. Mass is a crucial concept in physics, as it is a key factor in determining an object's behavior under the influence of forces.
Pycnometer: A pycnometer is a device used to precisely measure the density of a liquid or solid sample by determining its volume and mass. It is a critical tool in the study of density, a fundamental property of matter that is crucial in various scientific and engineering applications.
Relative Density: Relative density, also known as specific gravity, is the ratio of the density of a substance to the density of a reference material, typically water at 4°C and 1 atmosphere of pressure. It is a dimensionless quantity that provides information about the comparative heaviness or lightness of a substance compared to a standard.
Specific Gravity: Specific gravity is the ratio of the density of a substance to the density of a reference substance, typically water at a standard temperature and pressure. It is a dimensionless quantity that provides a measure of the relative density of a material, allowing for the comparison of the mass of a given volume of the substance to the mass of an equal volume of water.
Volume: Volume is the amount of three-dimensional space an object or substance occupies, typically measured in liters, cubic meters, or other units. It plays a crucial role in understanding how substances behave in different contexts, including their density, buoyancy, and how they respond to changes in temperature and pressure.