If the friction is 0 what happened

Friction and locomotion

In the following simulation you can see a block resting on a surface. The block can be, for example, a wooden box on a stone floor or a blocking car tire on a street. You can use the Surface materials Select from block and base. It doesn't matter which body has which surface.

Weight force and normal force

The black cross in the middle of the block marks the center of gravity of the block. In this focal point, two forces initially attack:

  • The Weight \ (\ vec F _ {\ rm {G}} \) of the log. The block is pressed onto the base by the force of weight. The Amount \ (F _ {\ rm {G}} \) of the weight force you can change it with the slider on the left.
  • The so-called Normal force \ (\ vec F _ {\ rm {N}} \). The normal force is the force with which the base "normal" (Latin norma "Measure", in the sense of the right angle), i.e. acts on the block perpendicular to the surface. The normal force arises from the fact that the base is slightly deformed downwards by the weight of the block, which, according to HOOKE's law, causes an upward force. The base deforms just enough that the normal force has the same amount as the weight. Thus weight and normal force compensate each other and the block rests on the base.

Tensile force and static friction force

With the second slider you can apply a tensile force \ (\ vec F _ {\ rm {Z}} \) to the block. At this moment you see other forces attacking the block:

  • The setTensile force \ (\ vec F _ {\ rm {Z}} \). The pulling force tries to pull the block to the right.
  • The so-called Static friction force \ (\ vec F _ {\ rm {HR}} \). It arises from the fact that the surfaces of the materials, viewed with a microscope, are never completely smooth, but rather rough. As a result, the particles "hook" to each other on the two surfaces. This then shows up macroscopically as a force that acts against the tensile force and prevents the block from moving. The Amount \ (F _ {\ rm {HR}} \) of the static friction force can be read off in the simulation on the left.

Size and maximum value of the static friction force

The amount \ (F _ {\ rm {HR}} \) of the static friction force is up to a certain value exactly as large as the amount \ (F _ {\ rm {Z}} \) of the tensile force. Since the two forces are directed in opposite directions, the static friction force \ (\ vec F _ {\ rm {HR}} \) and tensile force \ (\ vec F _ {\ rm {Z}} \) compensate each other. The block stays in peace.

If you increase the pulling force further, the pulling force will eventually be so great that the block will start moving. Then it is maximum value \ (F _ {\ rm {HR, max}} \) of the static friction force reached. From this moment on there is no longer any static friction, but sliding friction. Therefore we let the tensile force \ (\ vec F _ {\ rm {Z}} \) and the static friction force \ (\ vec F _ {\ rm {HR}} \) disappear from the simulation.