What affects the frictional force between sliding surfaces?

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Anderica Gilbert

GCSE Coursework

Investigate Frictional Force

Question: What affects the frictional force between sliding surfaces?

What is Friction?

Resistance to the motion of one surface over another is known as friction. The amount of friction is dependent on the smoothness of the contacting surfaces, as well as the force with which they are pressed together. Friction between unlubricated solid bodies is independent of speed and area. The coefficient of friction is obtained by dividing the force required to move one body over a horizontal surface at constant speed by weight of the body. Coefficients of rolling friction (e.g., the motion of a tire or ball bearing) are much less than the coefficient of sliding friction (back and forth motion over two flat surfaces). Sliding friction is thus more wasteful of energy and can cause more wear. Fluid friction occurs between the molecules of a gas or liquid in motion, and is expressed as stress. Unlike solid friction, fluid friction varies with speed and area. In general, lubrication is the substitution of low fluid friction in place of high solid-to-solid friction.

The kinetic frictional force always counteracts the motion of the object, and is independent of speed. No matter the speed of the object, as long as μ≤ 0 it experiences the same frictional force. Also, the kinetic frictional force is proportional to the normal force:


This equation is defines the coefficient of kinetic friction, μk is a property of the interacting materials, and is independent of orientation of the objects. Kinetic frictional force t only exists when one of the objects is moving and which is not depend on the force applied to the block

When the applied force is greater then the frictional force the block will move in the direction of the applied force. The limiting friction is the maximum force of friction between two surfaces.

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Factors that have an affect on frictional force are:

  • Mass of the object
  • Size
  • Surface texture
  • Surface area
  • Applied force
  • Lubrication
  • Angle the object is placed on

My investigation is to find the relationship between the pulling force and frictional force of an object weighing 100g to 1000g.

Hypothesis/Prediction

I predict that as the weight of the object increases so will the frictional forces, which will also increase the pulling force, therefore making the weight of the object, frictional force and the pulling force directly proportional.

Predicted Graph

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