1, introduction of force:

Force is one of the basic concepts in mechanics, and it is the fundamental reason to change the motion or deformation state of an object. In dynamics, it is equal to the product of the mass and acceleration of an object. Force can change the shape of an object, deform it and change its motion state.

2, the nature of the force:

(1) materiality: force is the action of an object (matter, mass) on an object (matter, mass). When an object is acted on by a force, another object will inevitably exert this effect on it, and this force cannot exist independently without this object.

(2) Reciprocity: The interaction between any two objects is always mutual, and the object that applies force must also be the object that applies force. As long as one object exerts a force on another object, the stressed object will in turn exert a force on the object exerting the force.

(3) Vectorality: Force is a vector with both magnitude and direction.

(4) simultaneity: the force is generated at the same time and disappears at the same time.

(5) Independence: The action of one force does not affect the action of another force.

Schematic diagram and type of force:

1. Schematic diagram of force:

The schematic diagram of force contains three elements: the magnitude, direction and action point of force. The way to accurately express the three elements of force with directed line segments is called the schematic diagram of force. The size is represented by the length of a graduated line segment, the direction is represented by an arrow, the point of action is represented by an arrow or the tail of an arrow, and the straight line along the direction of the force is called the line of action of the force.

The force diagram is used to calculate the force. When judging the size, we must pay attention to the scale of the line segment, because even if one line segment is longer than another, the scale of the long line segment is long, and the force represented by the short line segment is not necessarily smaller than that represented by the long line segment.

2, the type of force:

(1) electric field force: the interaction between charges occurs through an electric field. As long as there is charge, there is an electric field around it. The basic characteristic of electric field is that it has a strong influence on the charge put into it. This force is called electric field force.

(2) Centripetal force: the force that points to the center of the circle when an object moves in a circular motion. The centripetal force is an effective force, and its function is to produce centripetal acceleration. On the earth, the gravity on an object is actually one component of the gravity between the earth and the object, and the other component is the centripetal force when the object rotates with the earth.