Static Vs Kinetic Friction: Detailed Explanations

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This article discusses about the topic static vs kinetic friction. In this article, we shall discuss about friction first and then define static and kinetic friction.

In later sections we will differentiate between static and kinetic friction. We all know the meaning of friction and that it is related to something which opposes our motion. The reader need not worry if he/she does not the meaning of friction. This article will cover it all.

Static vs kinetic friction

The difference between static friction and kinetic friction is given in the section below.

Static frictionKinetic Friction
Static friction acts on an object which is at rest.Kinetic friction acts on an object which is moving.
Static friction is smaller than kinetic friction.Kinetic friction is greater than static friction mostly.
Static friction increases upto a maximum value and is equal to the force applied on the object.The value of kinetic friction is constant mostly.
 Static friction is represented by ks.Kinetic friction is represented by k.
Table: Difference between Static friction and Kinetic friction

What is friction?

As discussed in the above section, friction is the opposing force acting on the object while it is in motion or about to begin its motion.

Friction is mainly of two types depending upon the motion of the object. The two types of friction are kinetic friction and static friction. We shall study more about these types in later sections of this article.

static vs kinetic friction
Image: Simulation of Friction

Image credits: CaoHao, Friction between surfaces, CC BY-SA 4.0

What is static friction?

The term static refers to something which not moving and is at rest. Now we can say that this friction acts on an object when it is at rest. But how does friction oppose to an object which is not moving? Let us find out.

The object needs some velocity to start its motion. But the static friction does not allow the object to move unless it attains a certain velocity that is it won’t allow the object to move unless a certain amount of force is applied. This force has to be greater than static friction for the object to start its motion. This way the stationary object experiences friction.

What is kinetic friction?

The term kinetic refers to something which has kinetic energy or in simple terms is moving. The kinetic friction acts on the object when it is moving.

To keep the object in motion or move with same velocity, a force equal to kinetic friction has to be applied on the object. The object will come to rest if the force is uplifted from the object. Kinetic friction will keep opposing the motion and bring the object to rest.

Examples of friction

We can see friction in our daily lives. The frictional force is something which is everywhere. In all real cases, friction exists.

Let us see the different examples of frictional force that we see in our daily lives.

  • Braking– When we apply brakes on the car, the tyres stop rotating as a result of which they slide and rub with the road. Due to this sliding and rubbing, the frictional force comes into play. The vehicle stops after a while due to friction.
  • Cycling– The wheels of the cycle push the cycle forward due to the frictional force acting on it. Without friction, the wheels would have rotated at one place only without making the cycle move forward.
  • Walking– We are walking as a result of frictional force acting on our feet. If there was no friction we would have simply stayed at one place without moving forward.
  • Running– Running is just an extended form of walking. For running also, friction plays an important role. If there was no friction we would have stayed at one place like we run on treadmill.
  • Rubbing of hands– When we rub our hands against each other, we experience some resistance. This resistance caused is called as friction. The friction arises due to the irregularities on the surface of our hands.
  • Eraser– An eraser when rubbed against the paper generates friction. The eraser wears off due to the friction only.
  • Rolling process– Rolling process is a manufacturing process which is used for making thin sheets of metals and steels. The block of metal is passed between two sets of rollers. The metal block moves forward due to the action of friction acting on the metal.
  • Ball coming to rest after travelling a certain distance- When a ball is pushed, it starts moving and travels a certain distance. But we notice that the ball does not keep moving. This happens so because the ball experiences friction which makes the ball to come at rest.
  • Viscosity- Viscosity is the friction acting between two layers of fluid. The fluid layers while moving are slowed down due to viscosity. A liquid with high viscosity will move slowly and liquid with low viscosity will move faster.
  • Heat generation in tyres- When we apply brakes, we know that friction acts on the tyres. The heat is generated due to this friction. This is an example of frictional force being converted to heat energy.
  • Gear– Gears are an example of two irregular surfaces perfectly meshing each other for performing their applications. These gears have same module and conjugate profiles. Such that the teeth are meshed with each other. To keep the gears moving, we require an external force otherwise they will come to rest.
  • Pencil coming to rest after being rolled on paper- When we roll a pencil n the paper. The pencil rotates and moves upto a certain distance. After then it comes to rest. This is due to the fact that friction acts on the pencil which makes it come to rest.
  • Box comes to rest after sliding it– If we apply some force on the box, the box will start moving and as soon as we stop applying force on it, the box will move upto a certain distance due to inertia and then come to rest. This is due to the action of frictional force. The frictional force slows down the box and eventually it stops the motion of box.

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