What is the reference in the second year of junior high school physics textbook?

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.

References are used as references. Motion is absolute, and rest is relative. To describe a motion we need to first select an object as a reference, and once we have selected the object, then we need to assume that the object is immobile.

The reason why you can't understand it is because you are disturbed by the usual common sense, we usually say that the car is moving, the car is stopped, and there is also a reference, that is, the ground. In fact, when the car stops, you pass by, and you use yourself as a reference, the car is moving away from you.

Therefore, there is a conclusion: the reference object can be selected arbitrarily, and the same object may have different motion results if different reference objects are selected. We usually use the ground or an object that is not moving relative to the ground as a reference.

For the rest of the questions, you only need to compare the two objects given in the question. For example, when we see a building moving backwards in the car, the building is comparing the two sides with us, talking about the situation of the building, so we (the people in the car) are the references. The clouds block the sun, the clouds move, and the sun is the reference.

The moon is blocked by clouds, the clouds are moving, and the moon is the reference.

Reference: Another object used to determine whether an object is in motion or not, called a reference. An object, whether in motion or at rest, is relative to a reference.

For references, note the following:

1.Whether an object is in motion or at rest depends on which other object is used as the criterion. This object that has been selected as a standard is the reference.

2.To determine whether an object is moving or stationary, it is determined whether there is a change in position between the object and the selected reference. If there is a change in position, the object is in motion with respect to the reference object; If there is no change in position, the object is stationary with respect to the reference.

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A reference object is an object that is selected as a standard in advance in the process of studying mechanical motion, that is, an object that is selected as immobile in advance. For example, when studying automobile sports, the earth, houses, and trees are selected as references.