What are the basic tools for measuring time?

△ Time measurement tools:

1, in real life, ancient times: sundials, hourglasses, dripping hourglasses, pulse, etc. (see Knowledge Supplement and Expansion); modern times: clocks and watches (mechanical watches, quartz clocks, electronic watches, etc.).

2, in the sports field and laboratory often stopwatch (or stopwatch) to measure time;

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△ time unit of measurement:

International System of Units, the basic unit of time is the second (s); in real life, the common unit of time and: hours (h), minutes (min), milliseconds (ms), etc.;

Extended information:

Any periodical process can be adopted as a method of timing.

The period of a pendulum oscillating with slight amplitude at the same location is a definite constant, i.e., the period of a pendulum with a length of L at a location with a gravitational acceleration of g is:

The period of a pendulum with a length of L = 0.99295m at a location with a gravitational acceleration of g = 9.8m/s2 is T = 2s.

The pendulum clock thus became the main timekeeping instrument before the 19th century. The pendulum clock became the main timekeeping instrument before the 19th century.

This method of using the mechanical movement of the internal parts of the clock to keep time still has two serious defects: first, with the changes in temperature during the day and night and the four seasons, the pendulum undergoes thermal expansion and contraction, resulting in the instability of the pendulum length; secondly, due to the different values of gravitational acceleration at different latitudes and heights of the earth

(even if it is the same point on the ground, since the earth is in the middle of constant change), the value of gravitational acceleration is also different from the value of acceleration of the earth, so the pendulum length is also unstable. The acceleration of gravity is not a constant value), resulting in the calibration of the pendulum clock in the clock factory to the place of use will be out of calibration.

While people can adjust the length of the pendulum to continuously calibrate the period of the pendulum clock, the pendulum clock is not an ideal instrument for measuring time and timing, both in terms of the principle of time measurement and in terms of the operational practice of use.

Principle:

Electromagnetic punctuation timer is a kind of timekeeping instrument using AC power supply, its working voltage is 4~6V, the frequency of the power supply is 50Hz, it is every 0.02s to hit a point.

The electric spark timer is a timing instrument that uses spark discharge to make small holes in the paper tape and shows the point trace, using 220V AC voltage, when the frequency is 50Hz, it hits the point every 0.02s, when the electric spark timer works, the resistance to the guiding movement is relatively small, and it is smaller than the experimental error of the electromagnetic punctuation timer.

If the paper tape driven by the moving object passes through the punctuation timer, the points struck on the paper tape record the time of the object's movement, and the points on the paper tape correspondingly indicate the position of the moving object at different moments. By studying the intervals between the points on the paper tape, the motion of the object can be analyzed.

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