What are the external forces

1. The key is that you have to understand a physical "system" problem
there is no obvious boundary between internal force and external force, so it is hard to say which is external force and which is external force. Internal force does not affect the overall motion state of the object, but external force can affect the overall motion state of the object, and internal force and external force are relative. When separating the whole, internal force will also become external force, which depends on the specific. For example, when a bullet strikes a stationary board, the friction force is internal force in the overall analysis. However, if analyzed separately, the friction force is external force for the bullet, which hinders the bullet's movement. As a result, the bullet moves from the fast speed when it first enters the board to the slow speed later.

2. Forces outside a physical system. For example, consider two railway cars as a physical system. The tension between the two cars is internal force. The pulling force of the locomotive is the external force. These forces are relative. It depends on what you think. Common external forces are tension, elasticity, pressure, gravity, universal gravitation, and so on.

3. It's upstairs. Let me be more specific. That is to say, it depends on your research object. The research object is a small system of several objects, then the force between each object in the system becomes the internal force, and the force outside the system against the system is the external force. This is a simple understanding.

4. In short, the force outside the system is the external force, and the force inside the system is the internal force
for example, if the car is driving on the road, the friction between the car and the ground is the external force. If the whole earth and the car are taken as the system, the friction is the internal force

5. The combination of all external forces is the resultant force.

6.

The internal force is the interaction force in the system. For example, a compression spring is placed between two objects on a smooth horizontal plane, and the force exerted by the spring on the two objects after release is the internal force of the system composed of the two objects. The interaction force between the stars in the solar system is the internal force in the solar system

in a system composed of multiple objects, the force exerted on the system by objects outside the system is called external force, which refers to the effect caused by the external gravity (through the atmosphere, water, biology, etc.) from the earth, such as solar radiation, gravity, solar and lunar gravity. It includes weathering, erosion, transportation, sedimentation and consolidation diagenesis

There is a close relationship between the strength of the external force and the climatic factors, because the hydrological, vegetation and other factors that affect the development of the terrain are controlled by the climatic conditions

extended data

when an object deforms under the action of external force, the relative distance between internal particles changes, resulting in the change of internal force. The change of internal force is a kind of "additional internal force". The "additional internal force" is equal to the size of external force, but in the opposite direction, which is used to resist the change of object shape and size caused by external force, And try to make the object return to the state and position before deformation

There is a close relationship between the strength of the external force and the climatic factors, because the hydrological, vegetation and other factors that affect the development of the terrain are controlled by the climatic conditions. For example, in cold glacier covered areas, freezing thawing disintegration and glaciation are dominant; in arid areas, water flow is not significant, while wind sand is dominant; in warm and humid areas, water flow is the most active

7. Force is generally interpreted as: the interaction between objects
the external force is relative to the internal force. When it comes to internal force, it is inevitable to talk about the system. For example, if a car has a person on a smooth ground, the force between the car and the person belongs to the internal force, while the gravity of two people belongs to the external force

the interaction between objects in the system is internal force, And the force application side is outside the system, and the force of the object is external force

8. The external force and internal force are relative, the selected system is different, the force belongs to internal force and external force will be different!

9. The external force is the external force on the research object, and the internal force is the interaction between the parts of the research object. For example: for a train, the pulling force of the car to another car is internal force, while the resistance of the rail to the train is external force.

10. It depends on what you study.. If two objects as a system, then the friction between the two objects is the internal force of the system.. Two objects (assuming a and b), take a as the research object, then the friction force B gives a is the external force for a