top-rated free essay

# Coefficient of Friction

By margewill May 01, 2014 852 Words

Coefficient of Friction- Post Lab

Abstract

The purpose of the experiment was to determine to coefficient of friction on a block sliding across a horizontal plane, and on the same block sliding down an inclined plane. This was done by first testing block, and how much weight on a string was needed to move the block at a constant velocity using a pulley system. The block weighed 0.2385 kilograms, and needed a hanging mass of 0.05 kg to move at a constant velocity. This means the coefficient of friction is 0.37. The second block was tested on an inclined plane, and the angle was found at which the block would move at a constant velocity. The angle found was 230. Using the equation μk=tan θk we found the friction to be 0.42. The friction was different because there was more force required to keep the block sliding down the plane at a constant velocity.

Introduction

Frictional forces are universal, in which they are found between two solid surfaces in parallel contact. If an object moves over a surface, the force exerted on the object by the surface is called the Kinetic friction force. This force is in a direction opposite the direction the object is moving. The friction force is proportional to the normal force exerted by the surface on the body. The force’s relationship can be viewed by using the coefficient of kinetic friction, μk, in f=μkn, where f is the magnitude of the force of the friction, and n is the magnitude of the normal force. If the surface is flat, and horizontal, the normal force is equal to the weight of the object, due to the fact that because there is no acceleration in the normal direction, there is no net component in the opposite direction. If the surface is sloped, the normal force is the component of the weight, which is perpendicular to the surface.

If the object is pulled over the surface at a dynamic equilibrium (constant speed), the net force is equal to zero. This is because the normal force is equal to the weight of the body, and its opposite force, while as the force of friction is equal to the force of pulling the object, allowing for each force to cancel the other out, and giving a net force of zero. This means then that if the weight of the object and the force of pulling the object are known, then the normal force and the force of friction can be determined.

If the object is on an inclined plane, with the angle of the plane gradually increasing, then an angle will ultimately be reached at which the object will slide down the plane. At this angle, repose θs, the acceleration and the sum of all the forces acting on the body is zero. The component of the weight parallel to the incline is equal to the friction, while the component of the weight perpendicular to the incline is equal to the net force. By measuring the angle θs and using the equation μs=tan θs. we can find the coefficient of static friction μs. For a moving block, an angle can be found at value θk, where the block will slide down the plane at a constant velocity. At this angle, the acceleration is equal to zero, we can now claim that f=fk= μkn, where μk is the coefficient of sliding friction. We can then obtain μk=tan θk.

Procedure
1.Adjust the incline plane to be horizontal, determine the mass of the wooden block. 2.Run a string from the block over the pulley on the end of the plane. Adjust the pulley so that the string is parallel to the plane. 3.Hang the masses on the end of the string until there is sufficient force to move the block at a constant velocity after it begins moving. 4.The weight of the block is equal to the normal force and the weight of the masses, hung from the string, will be equal to the friction force. Record these values. 5.Repeat Step #4 but increase the mass of the blocks by placing 1, 2, 3, and 4kg on it. 6.Plot a graph showing the relationship of the normal force and the frictional force. Find the value of the coefficient of kinetic friction. Use the slope of the graph. 7.Find the angle at which the block will move down the slope at a constant velocity. Record angle. 8.Use this angle to find the coefficient of static friction.

Discussion

The purpose of the experiment was to find the coefficient of friction on a block moving along a horizontal surface, and an inclined plane. This was done using a pulley systems and using weights. For the block to move at a constant velocity across the horizontal plane 0.05kg of weight was needed for the string. In the second experiment the angle of the plane was increased to 23 degreers, therefor the block was sliding down at a constant velocity. By using this angle we were able to find the frictional force by using the equation μk=tan θk, giving us a force of 0.42N.

## Related Documents

• ###### Coefficients of Friction

...AP Physics Laboratory Coefficients of Friction Discussion: Friction is the force that resists motion and can be determined in either static situations or kinetic situations using the following equation: [pic] Static friction is the amount of friction that resists the start of motion and kinetic friction resists an object’s continue...

• ###### Friction

...FRICTION Friction is necessary for walking due to the following reason, As per Newton’s third law of motion, (every action has an equal and opposite reaction) we can walk if and only if the ground we are walking on push our feet back with a force. Now, as per the third law the ground would definitely push our feet back but if we are walking...

• ###### Lab: Coefficient of Friction, Static Friction, and Kinetic Friction

...purpose of this lab is to determine: the coefficient of friction between a rubber stopper and a wooden ramp the coefficient of static friction between a wooden block and a wooden ramp the coefficient of kinetic friction between a wooden block and a wooden ramp The design of this experiment was done by placing a rubber stopper / wooden block ...

• ###### Friction

...﻿ Friction Definition: Friction is the force resisting the relative lateral (tangential) motion of solid surfaces, fluid layers, or material elements in contact. Force of friction:- Friction is a force that is created whenever two surfaces move or try to move across each other. • Friction always opposes the motion or attempted mot...

• ###### Friction

...﻿Experiment 5: Friction Laboratory Report Charles Sanchez, Geminesse Sianghio, Ferguie Solis Department of Chemistry College of Science, University of Santo Tomas España Street, Manila Philippines Abstract In this experiment, a block of wood is used to observe friction on different surfaces such that an extra weight is also a...

• ###### Coefficient Of Kinetic Friction Lab

...﻿Coefficient of Kinetic Friction Objective: After completing this experiment, you should be able to measure the coefficient of sliding friction of an object that is located on an inclined plane. Apparatus: Inclined Plane Pulley attachment for plane Wooden blcok, with hook attached Meterstick Felt Set of masses String Protractor ...

• ###### An Experiment to Determine the Coefficient of Static Friction

...Name: Rodney Francis a/l Xavier ID: 1302969 Group members: Yuan Li Hong, Desmond Wong Practical Lecturer: Mr Zoheir Practical Group: 6 Part 1 Title: To determine the coefficient of static friction between two surfaces. Objectives: 1. To determine the relationship between the mass of load and the length of spring. ...

• ###### Friction

...For an object pulled or pushed horizontally, the normal force - N - is simply the weight: N = m g (2) where m = mass of the object (kg, slugs) g = acceleration of gravity (9.81 m/s2, 32 ft/s2) Frictional Coefficients for some Common Materials and Materials Combinations Materials and Material Combinations Static Frictional Coefficient ...