"Add or subtract" means positive or negative, and symbols can be used to represent the positive or negative of rational numbers, or to add and subtract logarithms in four operations. 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. The situation is more complicated.

In mathematics, if |a|=2 (absolute value), the actual value of a is 2. Numbers greater than 0 are called positive numbers. Positive numbers are usually preceded by a "+"symbol, which can usually be omitted. There are countless kinds of positive numbers, including positive integers, positive fractions and positive irrational numbers. Numbers less than 0 are called negative numbers, and negative numbers and positive numbers represent quantities with opposite meanings. Negative numbers are marked with a negative sign "-"and a positive number.

Symbol in physics is not a single concept. The symbols used in physics are sometimes equivalent to the symbols of rational numbers in mathematics, and sometimes used to express the nature and direction of physical quantities.

In physics,

Symbol is not a single concept in middle school physics. It can be used to represent the positive and negative of rational numbers, as well as the nature and direction of physical quantities. 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 meaning of physical quantity symbols 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 the 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. Arbitrarily give a 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".