frictional force

(noun)

Frictional force is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other.

Related Terms

  • isolated system
  • conservation

Examples of frictional force in the following topics:

  • 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.
    • If the maximum frictional force is greater than the force of gravity, the sum of the forces is still 0.
    • The force of friction can never exceed the other forces acting on it.
    • The frictional forces only act to counter motion.
  • Friction: Static

    • Another type of frictional force is static friction, otherwise known as stiction.
    • Like kinetic friction, the force of static friction is given by a coefficient multiplied by the normal force.
    • In general, the force of static friction can be represented as:
    • As with all frictional forces, the force of friction can never exceed the force applied.
    • Any force larger than that overcomes the force of static friction and causes sliding to occur.
  • Friction: Kinetic

    • The force of friction is what slows an object sliding over a surface.
    • The force of friction can be represented by an equation: $F_{\text{friction}} = \mu F_n$.
    • $F_n$ is called the normal force and is the force of the surface pushing up on the object.
    • Frictional forces always oppose motion or attempted motion between objects in contact.
    • Much of the friction is actually due to attractive forces between molecules making up the two objects, so that even perfectly smooth surfaces are not friction-free.
  • Internal vs. External Forces

    • External forces: forces caused by external agent outside of the system.
    • 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. )
  • 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.
    • Friction is not itself a fundamental force, but arises from fundamental electromagnetic forces between the charged particles constituting the two contacting surfaces.
    • Like friction, the force of drag is a force that resists motion.
  • 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.
    • Now, if the conservative force, such as the gravitational force or a spring force, does work, the system loses potential energy (PE).
    • 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 engineer in this instance has assumed a rigid body scenario and that the friction force is a sliding vector and thus the point of application is not relevant.
    • These forces can be friction, gravity, normal force, drag, tension, etc...
  • Drag

    • The drag force is the resistive force felt by objects moving through fluids and is proportional to the square of the object's speed.
    • Another interesting force in everyday life is the force of drag on an object when it is moving in a fluid (either a gas or a liquid).
    • You feel the drag force when you move your hand through water.
    • Like friction, the drag force always opposes the motion of an object.
    • Unlike simple friction, the drag force is proportional to some function of the velocity of the object in that fluid.
  • Problem Solving with Dissipative Forces

    • In the presence of dissipative forces, total mechanical energy changes by exactly the amount of work done by nonconservative forces (Wc).
    • Here we will adopt the strategy for problems 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.
    • 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).
  • 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.
    • The only two external forces acting on the car are its weight $w$ and the normal force of the road $N$.
    • Friction helps, because it allows you to take the curve at greater or lower speed than if the curve is frictionless.
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