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What is Friction?

Part of the Mechanics section of Coddy's Physics journey. Lesson 12 of 94.

Friction is the force a surface puts on an object that slides, or tries to slide, across it. It acts along the surface, against the sliding.

A box sliding to the right, the arrow v showing which way: friction f points left along the floor, the normal force N points up, perpendicular to the floor, and the weight mg points down

Friction acts along the floor, against the sliding. N is perpendicular to the floor.

Friction grows with the normal force N:

f = μN

μ has no unit and depends on the two materials.

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Challenge

A 4 kg box slides to the right across a floor, and nothing pushes it. The friction coefficient is μ = 0.25. Find how fast the box slows down: its acceleration a.

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

All lessons in Mechanics

1Vectors 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

4Kinematics in 1D

Position and DisplacementVelocityAccelerationMotion GraphsEquations of MotionRecap - Braking Car

7Kinematics and Newton

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

10Springs

Hooke's LawSprings in SeriesSprings in ParallelRecap - Spring Scale

13Momentum in 2D

Momentum as a Vector2D CollisionsExplosionsRecap - Billiards

16Gravitation

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

2Friction

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

5Vertical Motion

Free FallThrowing UpwardTime in the AirRecap - Dropped Ball

8Project: Delivery Drone

Mission BriefingTakeoff ThrustClimb to AltitudeCruise and BrakePackage Drop

11Elastic Energy

Elastic Potential EnergySpring LaunchersEnergy with SpringsRecap - Spring Launcher

14Circular Motion

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

17Final Challenges

Recap - Stunt RampRecap - Crash TestRecap - Space Probe

3Inclined Planes

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

6Projectile Motion

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

9Work and Energy

WorkKinetic EnergyWork-Energy TheoremGravitational PEConservation of EnergyPowerRecap - Roller Coaster

12Impulse and Momentum

MomentumImpulseConservation of MomentumElastic CollisionsInelastic CollisionsRecap - Air Track

15Simple Harmonic Motion

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