Mass Flashcards
Q1: What was the original definition of a kilogram in 1795?
A1: The kilogram was originally defined as the mass of one liter of water at 4°C, the temperature at which water is most dense.
Q2: Why was the water-based definition of the kilogram impractical?
A2: It was difficult to achieve in practice due to challenges with water’s surface tension, evaporation, purity, and the precision needed to measure the exact volume of water.
Q3: How was the kilogram redefined in 1799?
A3: In 1799, the kilogram was redefined based on the mass of a platinum cylinder to avoid the challenges of using water as a standard.
Q4: What was the International Prototype Kilogram (IPK) made from in 1889?
A4: The IPK was made from a platinum-iridium alloy and became the standard for the kilogram until 2019.
Q5: Where is the International Prototype Kilogram (IPK) stored?
A5: The IPK is stored under three bell jars, in a high-security vault in the International Bureau of Weights and Measures in Paris, France.
Q6: What problem was discovered with the IPK and its copies over time?
A6: Over time, the mass of the IPK and its copies changed slightly, likely due to handling, exposure to air, and other factors, causing inconsistencies in the definition of the kilogram.
Q7: What was the goal of the Avogadro Project in redefining the kilogram?
A7: The Avogadro Project aimed to redefine the kilogram by counting the number of atoms in a perfect silicon sphere, using X-ray diffraction to determine the atomic spacing.
Q8: Why was the silicon sphere approach unsuccessful in replacing the IPK?
A8: The uncertainties in counting the atoms in the silicon sphere were larger than the small fluctuations in the IPK’s mass, making it impractical to redefine the kilogram using this method.
Q9: What is the major problem with defining a kilogram based on a physical object?
A9: Defining a kilogram based on a physical object is problematic because physical objects can change over time due to environmental factors and handling, leading to inconsistencies.
Q10: Why is a fundamental constant-based definition of the kilogram preferred over a physical object?
A10: A fundamental constant-based definition, such as linking the kilogram to atomic properties, provides a more stable and universal standard that does not change over time, unlike physical objects.
