Coefficient of Static Friction Experiment

Coefficient of Static Friction between Two Surfaces

• The experiment aims to study friction between two surfaces in contact and determine the coefficient of static friction (initial μ) using the horizontal surface method.

Theory

• When a small pulling force (F) acts on an object (A) placed on a surface (B), a force is generated between the two bodies equal to the pulling force in magnitude and opposite in direction.
• When the forces increase and the body begins to move, the forces opposite to the pulling forces are called sliding friction forces (FK).
• The laws of friction state that:
  • Frictional force (F) is directly proportional to the compressive force between the two friction bodies, i.e., F = μN, where μ is the coefficient of friction and N is the compressive force.
  • Friction forces do not depend on the nature of the two contacting surfaces.

Finding the Coefficient of Static Friction by the Horizontal Surface Method

• Steps to find the coefficient of static friction:
  • Calculate the mass of the wooden piece (W) using a scale.
  • Place the wooden piece on the horizontal surface of the device and fasten its end with a fine thread passing on a roller.
  • Add suitable weights at the end of the rack, which represents M (Kg), until the wooden piece moves at a regular speed.
  • Calculate the value of the pulling force (F) = M × g (ground acceleration).
  • Put weights on top of the wooden piece so that the block of wood is heavy with it (W = W1 + W2).
  • Find the compressive force N from the equation N = W × g.
  • Repeat the previous steps for different weights and record the readings in a table.
  • Draw the relationship between the pulling force (F) on the y-axis and the compressive force N on the x-axis to get a straight line with an inclination representing the coefficient of friction (μ).

Finding the Coefficient of Sliding Friction by the Oblique Surface Method

• The coefficient of sliding friction (μκ) can be found on a horizontal surface by gradually increasing its inclination until the body begins to move, so the coefficient of friction is equal to the tangent of the angle at which the body began to move.

Discussion

• The relationship between the pulling forces and the compressive forces N can be discussed, and conclusions can be drawn from the graph.
• The coefficient of static friction (μ) can be compared with the coefficient of sliding friction (μκ) to determine which one is larger.