For problems 35-37, see Sample Problem D on page 139 of the text.

35. A 95 kg clock initially at rest on a horizontal floor requires a 650 N horizontal force to set it in motion. After the clock is in motion, a horizontal force of 560 N keeps it moving with a constant velocity. Find µs and µk between the clock and the floor. The coefficient of static friction is given by, ������������������������ = 0.70 ������������������������ ������������������������ ������������������������,������������������������������������ ������������������������

4.4 Practice
������������������������,������������������������������������ = 650 N , and ������������������������ = 560 N

The coefficient if kinetic friction is given by, ������������������������ = ������������������������ = 0.60 , where

, and

∴

36. A box slides down a 30.0° ramp with an acceleration of 1.20 m/s2. Determine the coefficient of kinetic friction between the box and the ramp. The magnitudes of the three forces are given by,
Fk Fn Fd

������������������������ = ������������������������ cos 30.0° N ������������������������ = ������������������������ sin 30.0° N

The net force is given by,

Therefore,

Recognizing that the mass cancels, substitute the values of the variables into the above equation. ������������������������ = 9.81 sin 30.0°−1.20 9.81 cos 30.0°

������������������������ =

������������������������������������������������ = ������������������������ − ������������������������ = ������������������������ sin 30.0° − ������������������������ ������������������������ cos 30.0° = ������������������������ ������������������������ sin 30.0°−������������������������...

...: Year 1 / Trimester 1
: 201401
Unit Code
Unit Title
: FHSC1014
: Mechanics
Tutorial 4: Application of Newton’s Laws.
1. The distance between two telephone poles is 50.0 m. When a 1.00 kg bird lands on the telephone wire midway between the poles, the wire sags 0.200 m. Draw a free-body diagram of the bird. How much tension does the bird produce in the wire? Ignore the weight of the wire. [614 N]
2. A 40 kg crate rests on a horizontal floor, and a 75 kg person is standing on the crate. Determine the magnitude of the normal force that (a) the floor exerts on the crate and (b) the crate exerts on the person. [(a) 1.13 x 103 N, (b) 735 N]
3. A worker stands still on a roof sloped at an angle of 45° above the horizontal. He is prevented from slipping by a static frictional force of 450 N. Find the mass of the worker. [85 kg]
4. A 4.0-kg bucket of water is raised from a well by a rope. If the upward acceleration of the bucket is 5.0 m/s2, find the force exerted by the rope on the bucket. [59 N]
5. A block is pressed against a vertical wall by a force , as the drawing shows. This force can either push the block upward at a constant velocity or allow it to slide downward at a constant velocity. The magnitude of the force is different in the two cases, while the directional angle is the same. Kinetic friction exists between the block and the wall, and the coefficient of kinetic friction is 0.250. The weight of...

...Session=2013-14
Physics Project
Topic: Friction
Submitted To; Submitted By;
Acknowledgement
The success and final outcome of this project required a lot of guidance and assistance from many people and I am fortunate to have got this all along the completion of my project work.
I respect and thank for giving me an opportunity to do the project work on ‘Friction’. I am extremely grateful to him for providing such a nice support and guidance.
At last, I want to thank my family and my friends for their support in this project.
Certificate
This is to certify that of class , has prepared and submitted the Project Report enclosed herewith under my direct and close supervision and that this is a individual piece of work done by him. It has not been submitted to any other school or university, nor has been published at any time earlier.
Date:
Teacher’s Sign- Principal Sign-
Index
Types of forces
Friction
Origin of force of friction
Types of frictional force
To calculate frictional force
Angle of repose equals to angle of friction
Types of Forces:
A force is a push or pulls acting upon an object as a result of its interaction with another object. There are a variety of types of forces.
Contact Forces
Action-at-a-Distance Forces
Frictional Force...

...the friction. Let us see about the friction here.
History
The classic rules of sliding friction were discovered by Leonardo da Vinci (1452–1519), but remained unpublished in his notebooks. They were rediscovered by Guillaume Amontons (1699). Amontons presented the nature of friction in terms of surface irregularities and the force required to raise the weight pressing the surfaces together. This view was further elaborated by Belidor (representation of rough surfaces with spherical asperities, 1737)[6] and Leonhard Euler (1750) who derived the angle of repose of a weight on an inclined plane and first distinguished between static and kinetic friction.. A different explanation was provided by Desaguliers (1725), who demonstrated the strong cohesion forces between lead spheres of which a small cap is cut off and which were then brought into contact with each other.
The understanding of friction was further developed by Charles-Augustin de Coulomb (1785). Coulomb investigated the influence of four main factors on friction: the nature of the materials in contact and their surface coatings; the extent of the surface area; the normal pressure (or load); and the length of time that the surfaces remained in contact (time of repose).[6] Coulomb further considered the influence of sliding velocity, temperature and humidity, in order to decide between the different explanations on...

...FRICTIONFriction 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 on a perfectly smooth ground which has no friction our force would simply cancel out the force reverted by the ground and we would fall.
If there was no friction, your foot would simply slide back as you tried to take steps, and you would go nowhere.
In order for something to move, it has to have a force moving it. That force has to have leverage, or friction.
when you walk you push the ground backward . your force is given on a large mass so the ground acceleration is negligible . now according newton third law of motion there is a reaction force which acts on less mass so you accelerate in other way you move . no if there was no friction and when you push the ground backward you would slip . friction force gives you the grip to move forward .
If you rub your hands together for several seconds, you’ll notice that your hands feel warm. That warmth is caused by a force called friction. When objects like your hands come in contact and move against each other, they produce 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 motion of one surface across another surface.
• Friction is dependant on the texture of both surfaces.
• Friction is also dependant on the amount of contact force pushing the two surfaces together (normal force).
Factors affecting friction:-
Friction depends partly on the smoothness of the contacting surfaces, a greater force being needed to move two surfaces past one another if they are rough than if they are smooth. However, friction decreases with smoothness only to a degree; friction actually increases between two extremely smooth surfaces because of increased attractive electrostatic forces between their atoms. Friction does not depend on the amount of surface area in contact between the moving bodies or (within certain limits) on the relative speed of the bodies. It does, however, depend on the magnitude of the forces holding the bodies together. When a body is moving over a horizontal surface, it presses down against the surface with a force equal to its weight,...

...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 added to the block of wood to measure the same units under the different surfaces. With also the use of lubircant a member of the group was asked to observe the effect adding a lubricant on friction. And with the use of a motion detector did the group observed air resistance.
Introduction
Friction is the force resisting the relative motion may it be unto solid surfaces, fluid layers, and even material elements that might cause a moving object to slow down when it is touching another object. Friction itself is not a fundamental force but arises from interatomic and intermolecular forces between the two contacting surfaces. In this experiment, the researchers are tasked to do five activities regarding friction which corresponds to the five laws of friction. The five laws states that it is dependent among the surface in contact, but within larger units friction is independent of velocity and the area of contact as long as there is an area of contact. it is also proportional and perpendicular to the normal force. These...

...quantitative measure of inertia of a body which is its resistance to rate of change of velocity. For a body with high inertia, the acceleration will be small. For a body with small inertia, the acceleration will be large.[1] The equation for the force is F= Mass x Acceleration, If you rearrange the force equation to solve for acceleration, you can see that if the size of the force doubles, then so does the size of the acceleration (if you push twice as hard, the object accelerates twice as much), and if the mass doubles, then the acceleration halves (if the mass is twice as big, it accelerates half as much).
If a car tried to drive up a slope it will have resistance acting against motion up the slope. Mass x Gravity x Cos* would gives us a friction force of the weight of the car on its tyres against the surface that the car was trying to drive up, and we would also have the resolved body weight of the car pulling it back down the slope. Resolved body weight would = Mass x Gravity x Sin *. When dealing with tractive force motion up a slope and down a slope has its advantages and disadvantages. When driving a truck up a slope the resolved weight of the truck will act against the motion of the truck and will pull the truck back down the slope. If the truck had no hand brake or brakes it would need a traction force at its wheels supplied by the engine just to hold the truck in its same position without moving otherwise the resolved body weight of the truck...

...Coefficient of Friction Lab
Abstract
The resisted force that acted along the tangent of two surfaces that were in contact was called friction. Friction was opposed to motion, and it acted in the opposite direction, where the surface of the object slid against the surface of the other object. The two types of friction that exist were called static friction and kinetic friction. When two surfaces are at rest with each other, but a push is caused to convey one of the surfaces to slide over the other was called static friction. However, the friction that was used in the lab was kinetic friction. Kinetic friction occurred when two surface were moving with contact to each other. The coefficient of kinetic friction is a constant shown as μk. The kinetic frictional force (fk) was given by the following equation: (fk= μkN), where N represented the normal force, which was the force that each body exerts on the other body, and acts perpendicular to each surface. The way that friction force is calculated is by the followed calculation: Ff=μFN, where (μ) was the coefficient of friction and (FN) was the normal force. Now in order to pinpoint the force of friction, the coefficient of friction should be figured out first. Now the way that the coefficient of...