Depth 1 · 36 s
Feathers or sand
Two boxes the same size, one of feathers and one of sand. Size doesn't tell you how much stuff is in a thing - its mass. A balance does, and pieces of known mass turn it into a measurement - in grams and kilograms. From 1889 to 2019 the kilogram was one metal cylinder near Paris.
About this video
Two boxes are the same size, one full of feathers and one full of sand. Which has more in it? Looking won't tell you, because size isn't the amount of stuff. The amount of matter a thing is made of is its mass, and to measure it you need a balance: the pan with more mass goes down.
To put a number on mass, add pieces of known mass to the other pan until the balance is level. Those pieces are units, grams: an apple is about 200 g, a paper clip about 1 g, and 1,000 g make a kilogram. This animation ends with the history of the kilogram itself. From 1889 to 2019 it was defined by one metal cylinder, Le Grand K, kept in a safe near Paris; today it is defined by a constant of nature.
This video shows depth 1 of Mass.
Learn MassTranscript
- 0:00Two boxes, the same size. Which one has more in it?
- 0:04One is full of feathers, the other of sand.
- 0:09How much stuff something is made of is its mass.
- 0:13A balance shows it: the side with more mass goes down.
- 0:17Add pieces of known mass to the other pan until it's level.
- 0:22Those pieces are units: grams. A thousand make a kilogram.
- 0:26From 1889 to 2019, the kilogram was one metal cylinder near Paris.
- 0:31Size can fool you. Mass is measured.