Length

Question 1

Q5: What was the original 1791 definition of the meter?

Answer 1

A5: The original meter was defined as one ten-millionth of the distance from the equator to the North Pole, along a meridian passing through Paris.

Question 2

Q6: Why was the original 1791 meter definition problematic?

Answer 2

A6: The original definition was problematic because Earth’s shape isn’t constant (due to rotation, erosion, and geographical differences), and it wasn’t a universal standard applicable outside of Earth.

Question 3

Q7: What was the meter redefined as in 1889?

Answer 3

A7: In 1889, the meter was redefined as the length of a platinum-iridium alloy bar stored in France.

Question 4

Q8: Why was the 1889 platinum-iridium meter bar definition not ideal?

Answer 4

A8: It wasn’t ideal because no two bars could be made exactly identical, physical objects could change over time (due to temperature, oxidation, etc.), and it wasn’t a universal constant.

Question 5

Q9: How was the meter redefined in 1983?

Answer 5

A9: The meter was redefined as the distance light travels in a vacuum in 1/299,792,458th of a second, based on the speed of light.

Question 6

Q10: Why is the current definition of the meter superior to previous definitions?

Answer 6

A10: The current definition is superior because it is based on the universal constant of the speed of light, which is the same everywhere and does not change over time, making it much more reliable than physical objects.

Question 7

Q11: What is the relationship between time and the definition of the meter?

Answer 7

A11: The meter is derived from the speed of light and requires precise time measurement using atomic clocks. By knowing the time it takes for light to travel, scientists can accurately determine the meter.

Question 8

Q12: Why did scientists choose the awkward number 1/299,792,458 when defining the meter?

Answer 8

A12: Scientists chose this specific number to keep the new definition of the meter as close as possible to the length of the old platinum-iridium bar used as the standard before 1983.

Question 9

Q13: What is one of the main arguments against using a physical object to define units like the meter?

Answer 9

A13: Physical objects can degrade over time, change slightly due to factors like temperature or oxidation, and are not universal, which makes them unreliable for consistent, long-term use.

Question 10

Q14: How did the redefinition of the meter change how we calculate the speed of light?

Answer 10

A14: Before 1983, the meter was based on a physical object, and the speed of light was calculated based on that definition. After 1983, the speed of light was fixed, and the meter was redefined based on that constant.

Question 11

Q15: What role does the speed of light play in modern time and distance measurement?

Answer 11

A15: The speed of light is a fundamental constant used to define the meter, and precise time measurement (from atomic clocks) is required to measure the distance light travels, allowing accurate distance and time measurements.