J
| joist | joists are small wall-to-wall metal beams or horizontal timbers that support floors and ceilings. these joists may be made of concrete, wood or steel and are often supported by beams. |
| joule (or j) | the physical measurement for work. one joule equals the work needed to lift one kilogramme ten centimetres off the ground; it can also be used to measure heat energy. one kilocalorie, an older energy unit, equals 4.1868 kilojoules |