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Kinetic Friction

Part of the Mechanics section of Coddy's Physics journey. Lesson 17 of 97.

Once an object slides, kinetic friction acts on it, against the motion:

fk=μkNf_k = \mu_k N

When the crate slides at a steady speed in a straight line, the push balances kinetic friction.

A sled pulled to the right at a steady speed, the arrow v showing which way: the pull F and the kinetic friction f are arrows of the same length in opposite directions, N points up and mg points down

Steady speed in a straight line: the pull F and kinetic friction f have the same size.

challenge icon

Challenge

You push a 25 kg25\ \mathrm{kg} box to the right across a floor, and it slides at a steady speed in a straight line. The kinetic friction coefficient is μ=0.3\mu = 0.3. Find your push FF.

Try it yourself

Physics diagram: crate, vec; arrows v

Solve for FF

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This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Mechanics

1Introduction

What is Physics?Your First EquationTurning a Rule Around

4Inclined Planes

Forces on an InclineGravity ComponentsFrictionless InclineIncline with FrictionWill It Slide?Recap - Ramp Challenge

7Projectile Motion

Independent AxesHorizontal LaunchLaunch at an AngleRange and Max HeightRecap - Hit the Target

10Work and Energy

WorkKinetic EnergyWork-Energy TheoremGravitational PEConservation of EnergyPowerRecap - Roller Coaster

13Impulse and Momentum

MomentumImpulseConservation of MomentumElastic CollisionsInelastic CollisionsRecap - Air Track

16Simple Harmonic Motion

What is SHM?Mass on a SpringThe PendulumSHM GraphsEnergy in SHMRecap - Oscillator

2Vectors and Newton's Laws

Right TrianglesWhat is a Vector?Adding VectorsAxes and DirectionsVector ComponentsForces Around UsFriction and TensionNewton's First LawNewton's Second LawNewton's Third LawRecap - Net Force

5Kinematics in 1D

Position and DisplacementVelocityAccelerationMotion GraphsEquations of MotionRecap - Braking Car

8Kinematics and Newton

From Forces to MotionFrom Motion to ForcesTwo-Stage MotionRecap - Elevator

11Springs

Hooke's LawSprings in SeriesSprings in ParallelRecap - Spring Scale

14Momentum in 2D

Momentum as a Vector2D CollisionsExplosionsRecap - Billiards

17Gravitation

Law of GravitationGravity and AltitudeSatellitesKepler's LawsGravitational EnergyEscape VelocitySatellite EnergyRecap - Mission to Orbit

3Friction

What is Friction?Static FrictionKinetic FrictionFriction and Newton's LawsRecap - Sliding Crate

6Vertical Motion

Free FallThrowing UpwardTime in the AirRecap - Dropped Ball

9Project: Delivery Drone

Mission BriefingTakeoff ThrustClimb to AltitudeCruise and BrakePackage Drop

12Elastic Energy

Elastic Potential EnergySpring LaunchersEnergy with SpringsRecap - Spring Launcher

15Circular Motion

Uniform Circular MotionCentripetal AccelerationHorizontal CirclesVertical CirclesLoop the LoopRecap - Car on a Curve

18Final Challenges

Recap - Stunt RampRecap - Crash TestRecap - Space Probe