There are five basic entities that elementary children measure in science: Length, volume, weight or mass, temperature, and time. Length is the distance between two points. Examples of length would be the height of a person, the length of a desk, or the distance between two buildings such as the distance between Westlake Hall and the library. Length is the measurement that is necessary for finding area. Length can be measured in metric units or conventional units. The basic metric unit of length is the meter. A meter is defined today as the distance light travels in 1/299,792,458 of a second. The basic unit of length in the conventional system is the foot. Children should be encouraged to measure objects within the classroom using a variety of instruments. It is very important that children gain the idea that length can be quantified and things can be measured. .
The volume of something is how much space it takes up. Volume can be measured in terms of length or in terms of its own units. The basic metric unit for volume is the liter. The basic unit of volume in the conventional system is the quart. Children often have trouble understanding that the amount of material in something does not change when it's shape changes. Calculating volume by displacement is a very advanced concept. There are many children in the upper grades that cannot understand it. An example of displacement is taking a long skinny glass and filling it with a cup of water and taking a short wide glass and filling it with a cup of water and asking students which one has more water. Students would be likely to say the long skinny glass because the water level looks higher than in the short glass when in reality, both glasses have the same amount of water in them.
There is a difference between weight and mass. Weight is the pull of gravity on something, mass is the amount of material in that something. Weight depends on the strength of gravity.