Friction - a phenomenon we encounter in everyday life constantly.Determine friction harmful or helpful, it is not possible.Make even step on the slippery ice by heavy exercise, on the rough surface of the asphalt walk pleasure.Details vehicles without lubrication wear out much faster.
study of friction, knowledge of its basic properties allows a person to use it.
friction force physics
force generated by motion or attempted motion of one body on the surface of another, directed against the direction of motion applied to moving bodies, called the friction force.Module frictional force, the formula of which depends on many parameters, vary depending on the type of resistance.
has the following types of friction:
• rest;
• slip;
• rolling.
Any attempt to budge a heavy object (cabinet, stone) leads to the exertion of man.In the movement of the subject does not always lead.It prevents this static friction.
Standstill
calculation formula friction force does not allow it to determine with sufficient accuracy.In virtue of Newton's third law of force resistance value of peace depends on the applied force.
With increasing force and the frictional force increases.
0 & lt;Ftr.pokoya & lt;Fmax
Static friction prevents the nails driven into the tree to fall;buttons, thread sewn firmly held in place.Interestingly, it allows a person to walk the resistance of the rest.And it directed the course of human movement, contrary to the general state of affairs.
slip phenomenon
With increasing external force driving the body to a value of maximum force of static friction is in motion.Strength of sliding friction is considered in the process of sliding along the surface of the body of another.Its value depends on the properties of the interacting surfaces and the vertical force acting on the surface.
calculation formula sliding friction: F = μR, where μ-factor of proportionality (sliding friction), P - power of the vertical (normal) pressure.
One traffic control forces - the force of friction, the formula of which is recorded using the reaction force.Due to the implementation of Newton's third law of force normal pressure and ground reaction equal in magnitude and opposite in direction: P = N.
Before you find the frictional force, a formula which takes on a different appearance (F = μ N), determine the strength of the reaction.
coefficient of resistance when sliding introduced experimentally for two rubbing surfaces depends on the quality of their treatment and the material.
table.The coefficient of resistance for different surfaces
| № paragraphs | interacting surfaces | value of the coefficient of sliding friction |
| 1 | steel + ice | 0,027 |
| 2 | Oak + oak | 0,54 |
| 3 | leather + iron | 0,28 |
| 4 | Bronze+ iron | 0,19 |
| 5 | Bronze + Iron | 0,16 |
| 6 | Steel + Steel | 015 |
greatest strength of friction, the formula of which was written above, it can be determined as well as the force of friction.
This becomes important in solving problems of the determination of the driving forces of resistance.For example, the book driven hand pressed on, slide under the force of resistance of rest that occurs between the hand and the book.The resistance depends on the strength of the vertical pressure on the book.
phenomenon rolling
transition of our ancestors from the scraper to the chariots considered revolutionary.Invention of the wheel - the greatest invention of mankind.Rolling friction that occurs when the motion of the wheel on the surface, is much inferior to the value of slip resistance.
emergence of forces of rolling friction forces associated with normal pressure on the surface of the wheel is of the nature that distinguishes it from slipping.Due to the small deformation of the wheel there are different sizes of pressure forces in the center of the site and formed at the edges.This difference determines the strength and the emergence of resistance to rolling.
calculation formula of rolling friction is usually taken similar to the process of sliding.The difference can be seen only in the values of the coefficient of resistance.
Nature resistance
If you change the roughness of the rubbing surfaces and changing the value of the friction force.With a large increase in the two adjoining surfaces look like bumps with sharp peaks.In imposing it protruding parts of the body come into contact with each other.The total contact area is small.When driving or attempting to motion of bodies "peaks" create resistance.The magnitude of the friction force does not depend on the surface area of contact.
appears that two perfectly smooth surfaces should not feel resistance completely.In practice the friction force in this case is maximized.This is explained by the nature of the discrepancy origin forces.This electromagnetic forces between atoms interacting bodies.
mechanical process, not accompanied by friction in nature, is not possible, because the possibility of "turn off" the electrical interaction of charged bodies there.The independence of the resistance forces on the relative positions of the bodies allows us to call them nonpotential.
Interestingly, the friction force, a formula that varies depending on the speed of interacting bodies is proportional to the square of the corresponding rate.By this force is the force of viscous resistance of the liquid.
Stir in liquid and gas
movement of a rigid body in a liquid or a gas, a liquid near a solid surface is accompanied by viscous resistance.Its appearance is attributed to the interaction of the layers of liquid entrained solid during the movement.Different speed layers - the source of the viscous friction.The peculiarity of this phenomenon - the absence of a liquid friction.Regardless of the magnitude of the external impact body is set in motion, being in the liquid.
Depending on the speed of movement of the resistance force is determined by the speed of movement, the shape of the moving body and the fluid viscosity.Stir in water and oil of the same body is accompanied by the greatness of the various resistance.
For small velocity: F = kv, where k - coefficient of proportionality depending on the linear dimensions of the body and the properties of the medium, v - velocity of the body.
liquid temperature also affects the friction therein.In cold weather warm up the car to warm the oil (viscosity decreases), and helped reduce the destruction of the adjoining parts of the engine.
Increased speed
significant increase in speed of the body may cause turbulent flow and the resistance rises sharply.Importance: the square of the speed, density and surface area of the body.The formula of the friction force becomes a different kind:
F = kv2, where k - coefficient of proportionality depending on body shape and properties of the medium, v - velocity of the body.
If the body to give a streamlined shape, turbulence can be reduced.The body shape of dolphins and whales - a perfect example of the laws of nature, affecting the rate of animals.
Energy approach
do the work of moving the body prevents the resistance of the medium.When you use the law of conservation of energy says that a change in the mechanical energy is equal to the force of friction.
work force is calculated by the formula: A = Fscosα, where F - force, under the action of which the body is moved by a distance s, α - the angle between the force and displacement.
obvious that the drag force is opposite to the movement of the body, where cosα = -1.The work of the friction force, which is given by the formula Atr = - Fs, the value is negative.This mechanical energy is transformed into internal (deformation, heating).
