friction

(noun)

A force that resists the relative motion or tendency to such motion of two bodies in contact.

Related Terms

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    • The instant sliding occurs, static friction is no longer applicable—the friction between the two surfaces is then called kinetic friction.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.

  • 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.

  • 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.

  • 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.

  • Conservation of Mechanical Energy

    • Conservation of mechanical energy states that the mechanical energy of an isolated system remains constant without friction.
    • Conservation of mechanical energy states that the mechanical energy of an isolated system remains constant in time, as long as the system is free of all frictional forces.
    • In any real situation, frictional forces and other non-conservative forces are always present, but in many cases their effects on the system are so small that the principle of conservation of mechanical energy can be used as a fair approximation.
    • Remember that the law applies to the extent that all the forces are conservative, so that friction is negligible.

  • General Problem-Solving Tricks

    • Ff: the friction force of the ramp.
    • There is a potential difficulty also with the arrow representing friction.
    • Now, the tip of the friction arrow is at the highest point of the base.
    • The intention however is not to indicate that the friction acts at that point.
    • These forces can be friction, gravity, normal force, drag, tension, etc...

  • Conservation of Energy in Rotational Motion

    • The stone continues to turn even after the motor is turned off, but it is eventually brought to a stop by friction.
    • To return to the grindstone example, work was done to give the grindstone rotational energy, and work is done by friction so that it loses kinetic energy.
    • However, the energy is never destroyed; it merely changes form from rotation of the grindstone to heat when friction is applied.

  • Internal vs. External Forces

    • There are mainly three kinds of forces: Gravity, normal force (between ice & pucks), and frictional forces during the collision between the pucks
    • With this in mind, we can see that gravity and normal forces are external, while the frictional forces between pucks are internal.
    • Without knowing anything about the internal forces (frictional forces during contact), we learned that the total momentum of the system is a conserved quantity (p1 and p2 are momentum vectors of the pucks. ) In fact, this relation holds true both in elastic or inelastic collisions.
    • (neglecting frictional loss in the system. )