| Aim | The aim of this experiment is to study the relationship between the force of limiting friction and normal reaction and to find the coefficient of friction between a block and a horizontal surface. |
| Apparatus Required | A flat surface such as a tabletop or floor A rectangular block of known mass A spring balance A set of weights A protractor Sandpaper |
| Theory | When two surfaces are in contact with each other, there is a force of friction between them. The force of friction is proportional to the normal reaction between the surfaces and is given by the equation: f = µN where f is the force of friction, N is the normal reaction, and µ is the coefficient of friction. In this experiment, we place a block on a horizontal surface and gradually increase the force acting on the block until it begins to move. The force at which the block starts to move is the force of limiting friction, and is given by the equation: flimit = µN By measuring the force of limiting friction and the normal reaction, we can calculate the coefficient of friction between the block and the surface. |
| Procedure | Place the flat surface on a level table or floor. Place the rectangular block on the surface and ensure that it is not moving. Attach the spring balance to the block and pull it horizontally until the block just starts to move. This is the force of limiting friction. Record the force of limiting friction in a table. To find the normal reaction, attach a set of weights to the block using the spring balance and measure the force required to lift the block off the surface. Record the normal reaction in the table. Repeat steps 3-6 for different weights until a range of normal reactions is obtained. Using the data obtained, plot a graph of force of limiting friction against normal reaction. Draw the best-fit straight line through the graph. Measure the gradient of the graph. The coefficient of friction is given by the gradient of the graph. |
| Observation and Result | Result: The result of the experiment is the coefficient of friction between the block and the horizontal surface. Observation: During the experiment, we observe that the force of friction is proportional to the normal reaction between the block and the surface. As we increase the normal reaction, the force of limiting friction also increases. By plotting the values of force of limiting friction and normal reaction on a graph, we can observe a linear relationship between these variables. The slope of this line can be used to determine the value of the coefficient of friction. We also observe that the coefficient of friction depends on the nature of the surfaces in contact. By using sandpaper to roughen the surface of the block or the horizontal surface, we can increase the coefficient of friction. Conversely, by using a smooth surface or applying a lubricant, we can decrease the coefficient of friction. |
