"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.
Detailed examples are explained as follows:
This symbol is usually used for the root of a quadratic equation with one variable, such as x? The solution of = 1 x = 1
The symbol here indicates that X can take two values, one is-1 and the other is-1.
Extended data:
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"; "Even if the acceleration is positive, even if the deceleration is negative.