Contents
Key Stage 4
Meaning
SI Units are the standard scientific units used by scientists around the world.
About SI Units
- SI stands for "Système international".
- SI units have been standardised around the world so that any experiment can be reproduced and so that components in machines are interchangeable.
- The USA does not always use SI Units. As a result of the confusion over units a space probe once crashed on Mars because one team of scientists was using inches and the other team was using hundredths of metre (centimetres).
The SI Units you should know are in the following table:
| Measurement | SI Unit |
| Distance, Displacement, Wavelength | metres |
| Time | seconds |
| Temperature | degrees Celsius or Kelvin |
| Mass | kilograms |
| Area | metres squared |
| Volume | metres cubed |
| Force, Weight | Newtons |
| Speed and Velocity | metres per second |
| Density | kilograms per metre cubed |
| Angle | degrees |
| Acceleration | metres per second per second |
| Moment | Newton Metres |
| Energy, Work Done | Joules |
| Electrical Charge | Coulombs |
| Electrical Current | Amps |
| Potential Difference | Volts |
| Resistance | Ohms |
| Radioactivity | Becquerels |
| Radiation Dose | Ohms |
| Frequency | Hertz |
| Magnetic Flux Density | Teslas |
| Moles | Mol |
| Concentration | Mol per decimeter cubed |
| Light intensity | Lux |