1. Unit of length:
In the International System of Units, the basic unit of length is the meter (m).
Other units: km, dm, cm, mm, μ m, nm, 1km=1000m; 1dm=0、1m;
Conversion relation: 1cm=0, 01m; 1mm=0、001m; 1μm=0、000001m; 1nm=0、000000001m。
2. Common tools for measuring length:
a scale.
Usage of scale:
(1) Pay attention to the zero scale line, minimum division value and range of the scale;
(2) At the time of measurement, the scale line of the scale shall be close to the object to be measured, and the position shall be upright without deflection. The zero scale line shall be aligned with one end of the object to be measured;
(3) When reading, the line of sight should be perpendicular to the ruler surface and aligned with the observation point, instead of looking up or down.
3. Unit of time:
In the International System of Units, the basic unit of time is the second (s).
The units of time are also hours (h) and minutes (min).
Conversion relationship: 1h=60min; 1min=60s。
4. The difference between the measured value and the true value is called error. We cannot eliminate the error, but we should try to reduce the error.
The error is related to the measuring instrument, measuring method and measuring person.
Methods to reduce errors: average multiple measurements, select precision measurement tools, and improve measurement methods.
Difference between error and error: error is not an error, error should not occur and can be avoided, and error can never be avoided.