Astrophysics units
- Syllabus
- 2024
- Topic
- —
- Level
- —
Learning objectives
Match astrophysics quantities to their units
A numerical value becomes a physical measurement only when its unit identifies the kind of quantity measured. In astrophysics, choose the unit from the quantity named, not from the size of the number.
| Physical quantity | Unit name | Symbol | Astrophysics example |
|---|---|---|---|
| mass | kilogram | kg | a satellite of mass 1200 kg |
| distance or orbital radius | metre | m | an orbital radius of 7.0 × 10⁶ m |
| speed | metre per second | m/s | an orbital speed of 7.5 × 10³ m/s |
| acceleration | metre per second squared | m/s² | an acceleration of 9.8 m/s² |
| force | newton | N | a gravitational force of 500 N |
| time or time period | second | s | an orbital period of 5400 s |
| gravitational field strength | newton per kilogram | N/kg | a field strength of 9.8 N/kg |
Selection method: identify the physical quantity first, then copy the matching unit symbol after the value. The words in the quantity are decisive: orbital speed uses m/s, orbital radius uses m, time period uses s, and gravitational field strength uses N/kg.
Keep the related units distinct. kg measures mass, whereas N measures force such as weight. m/s measures speed, whereas m/s² measures acceleration. N/kg measures gravitational field strength, not force. Unit symbols are case-sensitive and do not take plurals: write 500 N and 1200 kg, not 500 n or 1200 kgs.