It means sign. 1. symbol is not a single concept in middle school physics. Some symbols are equivalent to rational numbers in mathematics, while others are used to express the nature and direction of physical quantities, and the situation is more complicated. When students reach the final stage of high school, with the accumulation of knowledge, they often form negative migration, which leads to many mistakes in both positive and negative aspects of physical quantities. There are the following manifestations: (1) Simply understand the positive and negative of physics as the positive and negative of rational numbers, such as "speed -3m/s is less than speed 1m/s". (2) Unclear understanding of the symbolic meaning of physical quantities leads to errors, such as thinking that "the positive work direction is opposite to the negative work direction". (3) Not understanding the connotation of physical concepts leads to wrong judgment of symbols. For example, it is considered that "positive electric potential energy must be positive and negative electric potential energy must be negative". (4) Give any physical quantity or physical process positive or negative. For example, "there is a positive electric field around the positive charge and a negative electric field around the negative charge"; "Uniform acceleration is positive and uniform deceleration is negative". 2. For example: |a|=2 (absolute value) A is 2 3. How to sign? Suitable for most input methods: hold down Alt, enter 0 177 with the keypad, and the symbol will be printed. Use Baidu Pinyin Input Method: directly input Pinyin Fu Zheng, and you can enter plus and minus signs.