Science

Difference Between Static Friction and Kinetic Friction

Main difference

Friction is one of the most important forces that are responsible for movement on the Earth’s surface or, in other words, we can indirectly say that this is the force that has made life on Earth possible. As a common mindset, we know that friction is the resistance force that is always available when two or more than two bodies collide. In simple words, friction is the force that acts as an obstacle or in opposition to the movement of the object. There are four main types of friction, static friction, kinetic friction, rolling friction, and fluid friction. Static friction is the type of friction between bodies that keeps the object at rest, whereas when the force acting against friction exceeds static friction and the body goes into motion, Kinetic friction is the type of friction that slows down the moving object. The magnitude of static friction is always greater than kinetic friction. It means that more force is required to overcome static friction or to make the object move than in kinetic friction, where the applied force is to keep the object moving since it is already in motion.

Comparative chart

Static friction Kinetic friction
Definition Static friction is the type of friction between bodies that keeps the object at rest. When the force acting against friction overcomes static friction and the body is set in motion, kinetic friction is the type of friction that slows down the moving object.
Formula / equation k = μ k η max = μ s η
Magnitude The magnitude of the static friction is greater due to the greater value of its coefficient. The magnitude of kinetic friction is less compared to static friction, due to the lower value of its coefficient.
Others The value of static friction does not change as often and remains constant. The value of kinetic friction keeps fluctuating due to the continuous movement of bodies.

What is static friction?

It is the type of friction between bodies that keeps the object at rest. When you apply a force on the table to drag it and fail several times, the force that causes you to fail all these times is static friction, as it acts as an opponent or antagonist of the movement. To overcome or break this static friction, what you have to do is put more force and eventually the table goes into motion. When the objects in the rest begin to move, that means that the static friction has reached its maximum value. If an object is in the state of rest and no external force acts against it to make it move, the static friction is zero as the external force increases, the static friction increases, and in one stage the static friction reaches its maximum value and the objects begin to move. Static friction depends on μsμs (coefficient of static friction) and N (net normal body reaction). Static friction can be less than or equal to the product of μsμs (coefficient of static friction) and N (net normal body reaction). Static friction is exactly equal to the external force that is exerted on the object and is always opposite to the direction of motion.

What is kinetic friction?

When a body is set in motion after overcoming static friction or static friction reaches its maximum value, the force acting in opposition and slowing down the moving object is called kinetic friction. The magnitude of kinetic friction is low compared to the magnitude of static friction, that’s why it works as an obstacle between the object, but does not put it in the rest state, it just slows down the movement of the moving object. When you apply a force on the table to drag it and fail several times, the force that causes you to fail all these times is static friction, as it acts as an opponent or antagonist of the movement. To beat or cut this static friction, what you do is you put in more of your strength and eventually the table moves, and when you try to drag the table faster, you will feel a certain force that acts as an obstacle and slows it down. The force acting at that moment will be kinetic friction. The formula for the magnitude of the kinetic friction force fk = μkμk N, where μkμk is the coefficient of kinetic force of friction and N is the net normal reaction in the body.

Key differences

  1. Static friction is the frictional force that acts between the surfaces of two bodies that are at rest, that is, they are not moving.
  2. Kinetic friction is the type of frictional force that acts between the surfaces of two bodies that are in continuous motion.
  3. The value of static friction does not change.
  4. The value of kinetic friction keeps changing as objects are in motion.
  5. You need to reduce or overcome static friction to move an object.
  6. Kinetic friction is the resistance force between objects that move relative to each other.
  7. The coefficient of static friction is greater than the coefficient of kinetic friction.

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