friction

Examples of friction in the following topics:

• Friction: Static

  • Another type of frictional force is static friction, otherwise known as stiction.
  • Unlike kinetic friction, however, static friction acts to resist the start of motion.
  • Static friction is friction between two objects that are not moving relative to each other.
  • As with all frictional forces, the force of friction can never exceed the force applied.
  • The instant sliding occurs, static friction is no longer applicable—the friction between the two surfaces is then called kinetic friction.

• Friction: Kinetic

  • If two systems are in contact and moving relative to one another, then the friction between them is called kinetic friction.
  • The force of friction is what slows an object sliding over a surface.
  • The force of friction can be represented by an equation: $F_{\text{friction}} = \mu F_n$.
  • The coefficient of kinetic friction is typically represented as $\mu_k$ and is usually less than the coefficient of static friction for the same materials.
  • The coefficient of friction, too!

• Problem-Solving With Friction and Inclines

  • Recall that the force of friction depends on both the coefficient of friction and the normal force.
  • As always, the frictional force resists motion.
  • When not acted on by any other forces, only by gravity and friction, the frictional force will resist the tendency of the block to slide down the incline.
  • The force of friction can never exceed the other forces acting on it.
  • The frictional forces only act to counter motion.

• Reasons for Unemployment

  • There are three reasons for unemployment which are categorizes as frictional, structural, and cyclical unemployment.
  • The reason why the natural rate of unemployment is still positive is due to frictional and structural unemployment.
  • Frictional unemployment is the time period between jobs when a worker is searching for or transitioning from one job to another.
  • There is always at least some frictional unemployment in an economy, so the level of involuntary unemployment is properly the unemployment rate minus the rate of frictional unemployment.
  • Though economists accept that some frictional unemployment is okay because both potential workers and employers take some time to find the best employee-position match, too much frictional unemployment is undesirable.

• Applications of Newton's Laws

  • Net force affects the motion, postion and/or shape of objects (some important and commonly used forces are friction, drag and deformation).
  • Specifically, we will discuss the forces of friction, air or liquid drag, and deformation.
  • Friction is a force that resists movement between two surfaces sliding against each other.
  • When surfaces in contact move relative to each other, the friction between the two surfaces converts kinetic energy into heat.
  • Like friction, the force of drag is a force that resists motion.

• Types of Unemployment: Frictional, Structural, Cyclical

  • Frictional unemployment is another type of unemployment within an economy.
  • Frictional unemployment is always present to some degree in an economy.
  • Frictional unemployment is influenced by voluntary decisions to work based on each individual's valuation of their own work and how that compares to current wage rates as well as the time and effort required to find a job.
  • The natural rate of unemployment is a combination of structural and frictional unemployment.

• Problem Solving with Dissipative Forces

  • Using energy considerations, calculate the distance the 65.0-kg baseball player slides, given that his initial speed is 6.00 m/s and the force of friction against him is a constant 450 N.
  • Strategy: Friction stops the player by converting his kinetic energy into other forms, including thermal energy.
  • In terms of the work-energy theorem, the work done by friction (f), which is negative, is added to the initial kinetic energy to reduce it to zero.
  • The work done by friction is negative, because f is in the opposite direction of the motion (that is, θ=180º, and so cosθ=−1).
  • In the process, friction removes the player's kinetic energy by doing an amount of work fd equal to the initial kinetic energy.

• Blister

  • Blisters form when the skin has been damaged by friction or rubbing, heat, cold, or chemical exposure.
  • Friction blisters, caused by rubbing against the skin, can be prevented by reducing the friction to a level where blisters will not form.
  • Intense rubbing can cause a blister, as can any friction on the skin if continued long enough.
  • A friction blister is most common after walking long distances or wearing a new pair of shoes.

• Banked and Unbacked Highway Curves

  • In an "ideally banked curve," the angle $\theta$ is chosen such that one can negotiate the curve at a certain speed without the aid of friction.
  • In an "ideally banked curve," the angle $\theta$ is such that you can negotiate the curve at a certain speed without the aid of friction between the tires and the road.
  • For ideal banking, the net external force equals the horizontal centripetal force in the absence of friction.
  • Friction helps, because it allows you to take the curve at greater or lower speed than if the curve is frictionless.

• Employment Levels

  • Employment level, as defined by cyclical, structural and frictional unemployment, is one of the most important economic indicators.
  • Only some frictional unemployment would exist, where workers are temporarily searching for new jobs.
  • Frictional unemployment is the time period between jobs when a worker is searching for or transitioning from one job to another.
  • Frictional unemployment is always present in an economy, so the level of involuntary unemployment is properly the unemployment rate minus the rate of frictional unemployment.
  • New entrants (such as graduating students) and re-entrants (such as former homemakers) can also suffer a spell of frictional unemployment.