The types of forces are:

1. Gravity

The earth has a strange force, which can pull down objects in the air. This force is called "gravity". People jump hard, even if they jump high, they will soon fall to the ground. This is because they are affected by gravity. The gravity is called weight.

if the same object reaches the north or south pole, its weight will also change. Gravity is a component of universal gravitation between the earth and objects, which is directed vertically downward (only at the north and south poles), and the other component is the centripetal force when the objects rotate with the earth.

2. Elasticity

The force generated when an object is elastically deformed. For example, if you compress a spring, the spring resists your compression. This resisting force is elasticity.

3. Friction

When two objects that are in contact with each other and are pressed (and have a rough surface) have a tendency to move relative to each other, the contact surface generates a force that hinders the movement, and the direction is opposite to the direction of the movement of the objects. Friction must hinder the relative motion of objects and generate heat. When you throw a ball and the ball moves in the air, there is friction between the ball and the air, which we call air resistance.

When dust from space enters the earth's atmosphere, it moves violently with the air and rubs violently to give off light. This is a meteor. When the pressure is constant, the rougher the surface of the object, the stronger the friction; When the surface roughness of an object is constant, the greater the pressure, the stronger the friction.

People don't slip when walking because of friction. If the friction is too small, people will slip. Friction is divided into sliding friction, static friction and rolling friction, which are essentially the same. The force has nothing to do with the size of the stressed area.

4. Electric field force

The interaction between charges occurs through an electric field. As long as there is charge, there is an electric field around the charge. The basic property of the electric field is that it has a powerful effect on the charge put into it. This force is called electric field force.

5. Magnetic field force

includes Lorentz force acting on moving charge and Ampere force acting on current.

6. Pressure

The force acting vertically on the surface of an object. For example, if you put a book on a horizontal table, its effect on the desktop is pressure. Its size is equal to the weight of the book. However, if the book is placed on the inclined board, the pressure of the book on the inclined board is less than the weight of the book.

7. Centripetal force

The centripetal force is a force that points to the center of a circle when an object moves in a circle. Its effect is to produce centripetal acceleration. On the earth, the gravity on an object is actually a component of gravity between the earth and the object, and the other component is the centripetal force when the object rotates with the earth.

Centrifugal force is not an effect force or a property force, but an inertial force. There is no force applied to an object, and the force exists in a non-inertial reference system, which is not what the original entry said: "Centrifugal force is the reaction force of centripetal force, and they are equal in magnitude and opposite in direction. For example, when a hammer thrower rotates the hammer, his hand exerts centripetal force on the hammer, and the force felt by his hammer opponent is centrifugal force. "