Today’s soundtrack is *Opeth: Pale Communion*, a brilliant 70s-style prog rock album from the Swedish death metal masters.

This evening, I’m reading the fourth chapter of *Everything You Need to Ace Science in One Big Fat Notebook*, “SI Units and Measurements.”

SI units are the units used by the *systemé* * internationale*, which in English means the International System. So the SI is a universal set of measurements that scientists use. The base units of the SI system are presented in the book as follows:

Quantity | SI Unit |

length (or distance) | metre (m) |

mass | gram (g) |

weight (or force) | newton (N) |

volume (or capacity) | litre (L) |

temperature | Kelvin (K) |

time | second (s) |

electric current | ampere (A) |

amount of substrate | mole (mol) |

light intensity | candela (cd) |

As seen in the metric system, we can multiply SI units by using various prefixes. For example, “kilo-” means “1,000 of,” and “milli-” means “one thousandth of the whole.” This allows us to use appropriate units of measurement in various contexts.

Note that in the table, *mass* and *weight* have separate categories. This is because they are not the same. An object’s weight is determined by gravity; its mass is constant.

There are various tools that we can use to measure the properties of an object: trundle wheels to determine a distance, mathematical formulas to determine area or density (“density = mass/volume” (p. 44)) , water displacement to determine volume, beam balances to determine mass, a stopwatch to determine time, a thermometer to determine temperature, and so on.

Summary:

- The SI units for mass, length, and temperature are
~~Newtons~~grams, metres, and Kelvin. - The tool that I would use to measure the height of my dog is a metre stick or tape measure.
- We look into a graduated cylinder at eye level to take a volume reading of a liquid.
- The easiest tool used to measure mass is a scale.
- To find the volume of a rectangular solid, we calculate volume = (length)(width)(height).
- Weight is affected by gravity; mass is not.
- 50 centimetres is
~~0.005~~0.0005 kilometres. - “Volume” is how much capacity something has, or how much it can displace. Common volumes include the space in a duffel bag, how much gasoline the gas tank holds, how much milk is in the jug, etc.
- Water’s boiling point in Kelvin is
~~3371k~~373.15k. - If a paper clip is placed in a cup of root beer and it sinks to the bottom, we know that the paper clip has higher density. Since the density of water is approximately 1.0, we know that the paper clip’s density >1.