How can we know what to refer to?

In the study of mechanical motion, the object that is pre-selected and assumed to be immovable as a reference is called a reference. (Generally not based on the research object).

1. Objectivity - everything in the universe is in constant motion, and there is no absolutely stationary object. Usually, when we say that an object is moving or stationary, it is relative to another object (the reference object), and when describing the motion of the object, whether the reference object is mentioned or not, the reference object always exists, which is the objectivity of the reference object.

2. Presumptive - the reference object is only assumed to be immobile and not really immobile, and like other objects, it is also in eternal motion, which is the hypothetical nature of the reference object, and some students believe that the reference object is an immovable object. This perception is completely wrong.

3. Multiplicity - Since determining whether an object is moving or stationary, the key is to see what object is selected as a reference. Therefore, the motion we study is relative, and this is the multiplicity of the referent, that is, the study of the same object. Different references can be selected, and when different references are selected, the results of the description of the object's motion are often different.

For example, passengers sitting in a passenger car moving at a constant speed are stationary if the car is used as a reference; If you take the trees by the road as a reference, they are in motion.

Seek satisfaction.

Whatever object you stand on, you use that object as a reference.

Whichever object you use as a reference, you imagine yourself standing on it.

As follows:

Frame of reference. The choice is arbitrary, but it should be based on the principle of ease of observation and the simplicity of the description of the motion, and the ground is often chosen as the reference frame for the study of the motion of objects on the ground.

The general title is not indicated, and the reference system is indicated.

It's the ground. 1 It is assumed in advance that the frame of reference will not move.

2 Choose a different frame of reference and the results will vary.

3 The selection of a frame of reference can be arbitrary.

4 in the same frame of reference.

The four properties of the reference object:Arbitrary: The selection of the frame of reference is arbitrary, but should be based on the principle of ease of observation and as simple as possible in the description of the motion.

Variability: Different frames of reference are selected for the same movement, and the observations are generally different. For example, a passenger sitting in a moving car, with the ground as the frame of reference, the passenger is in motion, but if the car is used as the frame of reference, the passenger is stationary.

The reference object is relative, generally the one that is most conducive to motion analysis is selected as the reference, you can determine it according to the specific situation: for example, the moving car and the like are generally selected as the reference object of the ground or roadside street tree, and the object falling from a high place is generally selected as the reference object of the stationary building or pole next to it. Analyze it a few times a little more and you'll be familiar with it.

The 20 cm reference has the length of a pen.

The self-reference is a person's palm stretched flat, and the distance from the tip of the middle finger to the wrist is about 20 centimeters.

For a more obvious reference, look for an unopened fruit milk from Coca-Cola, which is 20 centimeters from the bottom of the bottle to the cap.

Reference Importance:

If the position of the object is changing relative to the frame of reference, it indicates that the object is moving relative to the frame of reference; If the position of the object is unchanged with respect to the frame of reference, it indicates that the object is stationary with respect to that frame of reference. The same object can have different states of motion relative to different frames of reference. In kinematics, the choice of frame of reference can be arbitrary.

The study and description of the motion of an object can only be carried out after a reference frame has been selected. How to choose a frame of reference must be considered on a case-by-case basis. For example, when an interstellar rocket is first launched, it mainly studies its motion relative to the ground, so the Earth is chosen as the reference object.

However, when the rocket enters the orbit around the sun, the sun is chosen as the frame of reference for the convenience of research.