# Length, Mass and Time Revision Notes

In addition to the revision notes for Length, Mass and Time on this page, you can also access the following Units and Measurements learning resources for Length, Mass and Time

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1.2Length, Mass and Time

In these revision notes for Length, Mass and Time, we cover the following key points:

• Knowledge on the definition, properties and units of length, mass and time
• The meaning of dimensional analysis and its importance
• How to find a formula using dimensional analysis
• What are the limitations of dimensional analysis use

## Length, Mass and Time Revision Notes

Units in science have their own hierarchy. This hierarchy or order of importance is established taking into account the frequency of their use in forming derived units. Thus, the units of length, mass and time appear in a very large number of combined units.

By definition, length is the measurement or extent of something from end to end; the greater of two or the greatest of three dimensions of an object. According to the most recent definition, a meter is defined as the distance traveled by light in vacuum during a time interval of 1/299, 792, 458 of a second.

Mass is the quantity of matter a body contains, as measured by its acceleration under a given force or by the force exerted on it by a gravitational field. In the SI system, the unit of mass is kilogram (kg). Kilogram is an arbitrary established unit of mass. The mass of a cylinder of platinum-iridium alloy kept in the International Bureau of weights and measures preserved at Serves near Paris, is called one kilogram.

By definition, Time is the indefinite continued progress of existence and events that occur in an apparently irreversible succession from the past, through the present, into the future. The unit of time in all systems of units is second (s). In scientific terms, the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of cesium-133 atoms is called one second.

Dimensional analysis is a method of analysis in which physical quantities are expressed in terms of their fundamental dimensions that is often used when there is not enough information to set up precise equations. However, Dimensional Analysis has an important drawback. Through this method, we are not able to identify dimensionless constants in a formula.

### Units and Measurements Calculators

The following Physics Calculators are provided in support of the Units and Measurements tutorials.