Tham khảo tài liệu 'science of everyday things vol. 2 - physics episode 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | DENSITY and Volume KEY TERMS ARCHIMEDES S PRINCIPLE A rule of physics which holds that the buoyant force of an object immersed in fluid is equal to the weight of the fluid displaced by the object. It is named after the Greek mathematician physicist and inventor Archimedes c. 287-212 . who first identified it. BUOYANCY The tendency of an object immersed in a fluid to float. This can be explained by Archimedes s principle. DENSITY The ratio of mass to volume in other words the amount of matter within a given area. MASS According to the second law of motion mass is the ratio of force to acceleration. Mass may likewise be defined though much less precisely as the amount of matter an object contains. Mass is also the product of volume multiplied by density. MATTER Physical substance that occupies space has mass is composed of atoms or in the case of subatomic particles is part of an atom and is convertible into energy. SPECIFIC GRAVITY The density of an object or substance relative to the density of water or more generally the ratio between the densities of two objects or substances. VOLUME The amount of threedimensional space an object occupies. Volume is usually expressed in cubic units of length. WEIGHT DENSITY The proper term for density within the British system of weights and measures. The pound is a unit of weight rather than of mass and thus British units of density are usually rendered in terms of weight density that is pounds-per-cubic-foot. By contrast the metric or international units measure mass density referred to simply as density which is rendered in terms of kilograms-per-cubic-meter or grams-per-cubic-centimeter. Comparing Densities As noted several times the densities of numerous materials are known quantities and can be easily compared. Some examples of density all expressed in terms of kilograms per cubic meter are Hydrogen kg m3 Air kg m3 Oak 720 kg m3 Ethyl alcohol 790 kg m3 Ice 920 kg m3 Pure water 1 000 kg m3 Concrete 2 300 kg m3 .
