We explain what friction or friction force is and what its causes are. Also, static friction and kinetic or dynamic friction.
What is friction?
Friction, friction force or friction force It is a force existing between two surfaces that are in contact and that opposes the movement, that is, has a direction opposite to movement. This force can be of two types: static (when it opposes the beginning of a slide) or dynamic (when it opposes relative movement).
The force of friction is not one of the fundamental forces of the universe, like gravity, but is due to the complex interaction between the surface of two objects in physical contact. We generally talk about friction for solid objects, but friction also exists in liquids: the effect of friction between the layers of a liquid substance defines its viscosity.
To set an object at rest in motion, the force that pushes it to move must precisely overcome the resistance exerted by friction, which is greater between rough and irregular surfaces than on smooth and polished surfaces.
On the other hand, if an object that is in contact with a surface, for example, a table, is pushed, and as a result it begins to move in the direction of the push, its speed will decrease as the friction force exerted by it decreases. the table exerts on it, defeats that of the initial push. This friction force depends on the mass of the bodies, so that Heavier objects show more friction than lighter ones.
Friction also has an effect on the surfaces in contact. It is often imperceptible, however the kinetic energy lost through friction It is transformed into heat, that is, the surfaces are heated by friction. Even both can suffer wear
Causes of friction
Friction may be due, first of all, to microimperfections between contacting surfaces which make it difficult to slide one over the other, even if they apparently cannot be perceived. This is why some surfaces have more friction than others.
Thus, the friction can be reduced mechanically by adding lubricants for example, or it can be increased, degenerating the surfaces in some way.
static friction
Static friction (Fand) is the force that tends to oppose the relative displacement between two surfaces in contact. It is the force that needs to be overcome to start the movement of an object. It is always less than or equal to the coefficient of static friction (which has an empirical value and depends on the material) between the two surfaces multiplied by the normal force.
This static friction is usually greater than the dynamic which explains why it is more difficult to start pushing heavy furniture on rough ground than to continue pushing it once it is already in motion.
Kinetic or dynamic friction
Dynamic friction (Fd) is the force that opposes the displacement of an object that is already in motion unlike static friction.
It is a constant magnitude since the amount of force needed to keep the motion going does not change as long as the acceleration is constant. Therefore, is equal to the coefficient of dynamic friction denoted by the Greek letter μmultiplied by the normal force.
The differences between static and dynamic friction are not fully understood on a physical level, but it is believed that static force is greater due to electrical attractions and microwelding between surfaces at rest.
Examples of friction
Examples of friction are countless. Friction It is that force that opposes us moving an old piece of furniture pushing it with our strength. It is also the force that will make a flat stone that we throw sideways on the surface of the water stop and jump.
friction force It's what brakes use to keep a car in place when we park it on a steep hill, and it is the same that, if we suddenly brake while driving the same car at high speeds, it will reduce the speed and displacement of the car by overcoming inertia.
Other common examples of friction involve the heat generated by friction as happens when we light a fire by rubbing two wooden sticks against each other, or when we suffer a burn from the friction of a rope in sudden movement when we were holding it in our hands.
Continue with: Newton's Laws
References
- “Friction” on Wikipedia.
- “What is the force of friction or friction” (video) in Educatina.
- “What is friction?” at Khan Academy.
- “Physics – What is friction?” (video) in Don't Memorise.
- “What is friction?” on Live Science.
- “What is friction?” on BBC Bitesize.
- “Friction (physics)” in The Encyclopaedia Britannica.
