Monday, December 4, 2023

# How To Do Friction Problems In Physics

## How Do You Measure The Coefficient Of Friction

How to solve friction problems in grade 11 physics SPH3U (3 of 3)

There are two easy methods of estimating the coefficient of friction: by measuring the angle of movement and using a force gauge. The coefficient of friction is equal to tan, where is the angle from the horizontal where an object placed on top of another starts to move. For a flat surface, you can pull an object across the surface with a force meter attached. Divide the Newtons required to move the object by the objects mass to get the coefficient of friction.

## Find The Normal Force On The Object

Find the normal force on the object. If the object is resting on a horizontal surface, the normal force is the same magnitude, or numerical value, as the force of gravity, F=mg, but in the opposite direction as the force of gravity. If the object is on a slanted surface, or other forces are acting on the object, you will have to take components, or directions, into account.

## How Does Friction Affect Motion

Friction is what makes motion possible. When one object moves against another, two opposite but equal forces are formed due to friction, without which you would be running on the spot. Friction also allows us to stop – when an object is slowed, friction turns the kinetic energy into thermal or vibrational energy. The more slippery a surface is , the slower the rate of this energy transfer is.

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## Coefficient Of Friction Problems Worksheet With Answers

Some of the worksheets below are Coefficient of Friction Problems Worksheet with Answers, Several Calculations involving coefficient of friction, types of friction like Rolling Friction, Sliding Friction, Fluid Friction, , Static and Kinetic Friction : Objectives -Distinguish the Difference Between Static & Kinetic Friction Solve Problems Involving Friction Effects and Static & Kinetic Friction Coefficients,

## Other Types Of Friction Rolling resistance is the force that resists the rolling of a wheel or other circular object along a surface caused by deformations in the object or surface. Generally the force of rolling resistance is less than that associated with kinetic friction. Typical values for the coefficient of rolling resistance are 0.001.One of the most common examples of rolling resistance is the movement of motor vehicle tires on a road, a process which generates heat and sound as by-products.

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## Applications Of Kinetic Friction

• Friction also plays a huge role in everyday occurrences like while rubbing of two objects takes place. The resulting motion converts into heat and thus resulting in the fire in some instances.
• It is also responsible for wear and tear and thats why we need oil to lubricate machine parts, as it reduces friction.
• When two objects are rubbed against each other, the frictional force is converted into thermal energy, in few cases giving rise to fire
• Kinetic friction is responsible for the wear and tear of machine parts, hence it is important to lubricate the machine parts with oil.

## What Would Happen In A World Without Friction

If there were no friction, there would be no anything. The friction that holds atoms together would disappear, so nothing would be able to form. Life wouldn’t exist, as atoms wouldnt be near each other long enough to form simple molecules. The world would become a dangerous place to live, as cars in motion would lose the ability to stop. Youd probably die as well, as your blood would steadily move around quicker and quicker. Good thing this scenario is physically impossible!

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## What Is The Difference Between Static Friction And Dynamic Friction

Static and dynamic friction differ with respect to movement. Static friction is the friction between two surfaces that are not moving relative to each other. If these two surfaces were moving relative to each other, it would be dynamic friction. For example, a block on a table experiences static friction. This continues as you incline the table until the block moves, at which point the friction becomes dynamic.

## But Wait Which Formula Do I Use

Net Force Physics Problems With Frictional Force and Acceleration

You look at your formula sheet and you have three different ones that are marked under the problems subject. How do you know which one to use?? Naturally, you begin panicking again.

Dont panic.

Physical equations didnt just land on scientists from the sky, all wrapped up nicely in mathematical formulation. They are derived from physical properties, and they are all interconnected. In most physics problems, there is more than one way to reach a solution, often meaning that more than one equation can work. In fact, in the vast majority of questions, no matter what equation you use assuming that it is relevant to the subject matter, and that you insert the proper variables you will reach a solution.

The way to know which equation to use depends on two main issues: the variables given to you in the equation and your experience. The more problems you solve, the more you will become familiar with strategies for picking the right formula. Until that happens, though, look for the formula that has the variable you already know and connects those to the one variable you are missing. If you have two missing variables, you will likely need two equations.

Slow down, look at your variable list, and find the right ones. Its like a puzzle, and the more you do it, the better you get at it.

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## What Is Kinetic Friction

Kinetic friction is defined as a force that acts between moving surfaces. A body moving on the surface experiences a force in the opposite direction of its movement. The magnitude of the force will depend on the coefficient of kinetic friction between the two material.

Friction is easily defined as the force that holds back a sliding object. The kinetic friction is a part of everything and it interferes motion of two or more objects. The force acts in the opposite direction to the way an object wants to slide. If a car has to stop, we apply brakes and that is exactly where the friction comes into play. While walking, when one wants to suddenly come to a halt, friction is to thank again. But when we have to stop in the middle of a puddle, things get harder since friction is less there and cannot aid one so much.

A Model For Kinetic Friction

## How To Solve Any Physics Problem

wikiHow is a wiki, similar to Wikipedia, which means that many of our articles are co-written by multiple authors. To create this article, 23 people, some anonymous, worked to edit and improve it over time. This article has been viewed 282,807 times.

Baffled as to where to begin with a physics problem? There is a very simply and logical flow process to solving any physics problem.

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## A More Detailed Look At Friction

Really, what is friction? You could say that when two surfaces come near each other , the atoms in surface B get close enough to interact with surface A. The more atoms that are interacting in the two surfaces, the greater the total frictional force. How do you get more atoms to interact from the two surfaces? Well, if you push the surfaces together you can get more atoms from A to be close enough to the atoms from B to interact. Yes, I am simplifying this a bit. However, the point is that contact area does indeed matter.

I am talking about contact area, not surface area. Suppose you put a rubber ball on a glass plate. As you push down on the rubber ball, it will deform such that more of the ball will come in “contact” with the glass. Here is a diagram of this.

Greater contact area means greater frictional force. If the contact area is proportional to the normal force, then this looks just like Amontons’ Law with the frictional force proportional to the normal force. Of course this model “breaks” when the contact area can no longer increase. As I add more and more mass onto the friction box, there is less and less available contact area to expand into. In a sense, the contact area becomes saturated. I suppose that if I kept piling on the weight, the friction force would eventually level out and stop increasing.

## Doing Your Best In Physics Class • 1Read the topic before the lecture. Ideally, you shouldn’t come across new physics concepts for the very first time in class. Instead, try, reading upcoming lessons in your textbook the day before they’ll be covered in class.XResearch source Don’t fixate on the precise mathematics of the topic at this stage, focus on grasping the general concepts and trying to grasp what is being discussed. This will give you a solid foundation of knowledge upon which you’ll be able to apply the mathematical skills you’ll learn in class.
• 2Pay attention during class. During class, the teacher will explain the concepts you encountered in your pre-reading and clarify any areas of the material that you don’t understand well. Take notes and ask plenty of questions. Your teacher will probably go through the mathematics of the topic. When he or she does so, try to have a general idea of “what’s happening” even if you don’t remember the exact derivations of each equation having this sort of “feel” for the material is a huge asset.
• If you have lingering questions after class, talk to your teacher. Try to make your questions as specific as possible this shows the teacher that you were listening. If the teacher isn’t busy, she or he will probably be able to schedule an appointment to go over the material with you and help you understand it.
• Tutors
• Third-party resources
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## Setting Equations For The Pulley

For cart M, the equation would be, T Fr = Ma or, T Mg = Ma

For the cylinder m the FBD and equation remain same as the previous case.mg T = ma .. Adding equation 1 and 2, mg Mg =a or, a = g/ from eqn 2, ;T = m = m = mg = mg or, T =/

So the acceleration of the cart isg/And the tension in the rope is /

We will add other pulley systems soon and study those as well. If you like this, please share as much as possible.

## Magnitude Of Kinetic Friction

The magnitude of kinetic friction fk is given by fk=kN, where k is the coefficient of kinetic friction.

As seen in Table 1, the coefficients of kinetic friction are less than their static counterparts. That values of in Table 1;are stated to only one or, at most, two digits is an indication of the approximate description of friction given by the above two equations.

Table 1. Coefficients of Static and Kinetic Friction
System
0.4 0.02

The equations given earlier include the dependence of friction on materials and the normal force. The direction of friction is always opposite that of motion, parallel to the surface between objects, and perpendicular to the normal force. For example, if the crate you try to push has a mass of 100 kg, then the normal force would be equal to its weight, W =;mg = = 980 N, perpendicular to the floor. If the coefficient of static friction is 0.45, you would have to exert a force parallel to the floor greater than;fs =sN = N = 440N;to move the crate. Once there is motion, friction is less and the coefficient of kinetic friction might be 0.30, so that a force of only 290 N fk =;kN = = 290N;would keep it moving at a constant speed. If the floor is lubricated, both coefficients are considerably less than they would be without lubrication. Coefficient of friction is a unit less quantity with a magnitude usually between 0 and 1.0. The coefficient of the friction depends on the two surfaces that are in contact.

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## Can Heat Up Parts

The Law of Conservation of Energy states that the amount of energy remains constant. Thus, the energy that is “lost” to friction in trying to move an object is really turned to heat energy. The friction of parts rubbing together creates heat.

You’ve seen how people will try to start a fire by vigorously rubbing two sticks together. Or perhaps you’ve seen an automobile spin its wheels so much that the tires start to smoke. These are examples of friction creating heat energy. Just rub your hands together to create the same effect.

Besides the problem of losing energy to heat, there is also the threat of a part overheating due to friction. This can cause damage to a machine.

## Friction Is Just A Model

How to solve friction problems in grade 11 physics SPH3U (2 of 3)

How about another experiment? In this experiment, I am going to put an object on an moveable plane. I can then increase the angle of inclination until this block just starts to slide. At the moment it starts to slide, I can calculate both the normal force and the friction force .

Here is a force diagram at the instant the block starts to slide.

Just at the instant this thing starts to slide, all of these forces still have to add up to the zero vector . That means that the component of the gravitational force perpendicular to the plane must be equal to the magnitude of the normal force and the component parallel to the plane must be equal to the frictional force.

With just the mass and the sliding angle, I can get both the frictional force and the normal force. How can I calculate the coefficient of friction? What if I made a plot of friction vs. normal force for the same surface but with different masses? If the normal force and the frictional force are really proportional then this data should be linear with the slope of the line being the coefficient of friction.

It’s simple, right? Ok. Let’s do this. In order to keep everything the same except for the mass, I am going to put masses into one of these small boxes.

Here is a plot of friction force vs. normal force for both surfaces. The error bars are calculated from the standard deviation in angle measurements.

#### Content

This shows that the “standard” friction model is just that – a model. Models were meant to be broken.

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## Limitations Of The Coulomb Model

The Coulomb approximation follows from the assumptions that: surfaces are in atomically close contact only over a small fraction of their overall area; that this contact area is proportional to the normal force ; and that the frictional force is proportional to the applied normal force, independently of the contact area. The Coulomb approximation is fundamentally an empirical construct. It is a rule-of-thumb describing the approximate outcome of an extremely complicated physical interaction. The strength of the approximation is its simplicity and versatility. Though the relationship between normal force and frictional force is not exactly linear , the Coulomb approximation is an adequate representation of friction for the analysis of many physical systems.

When the surfaces are conjoined, Coulomb friction becomes a very poor approximation . In this case, the frictional force may depend strongly on the area of contact. Some drag racing tires are adhesive for this reason. However, despite the complexity of the fundamental physics behind friction, the relationships are accurate enough to be useful in many applications.

## Newtons Laws And Weightlessness

#### 6.25 A person stands on a scale in an elevator. As the elevator starts, the scale has a constant reading of 591 N. As the elevator later stops, the scale reading is 391 N. Assume the magnitude of the acceleration is the same during starting and stopping, and determine the weight of the person, the persons mass, and the acceleration of the elevator.

Analyze the problem:

The problems mentions two stages of motion: starting of motion and stopping of motion for an elevator. The given forces are the normal forces or the readings of the scale.

What are given information:

• Normal force when elevator is starting = 591 N
• Normal force when elevator is stopping = 391 N
• What the problem need:

From Serway and Jewett Physics for Scientists and Engineers with modern physics, 9th edition

Lets analyze the wording of the problem:

• A conical pendulum is a swinging pendulum that can rotate around an axis.;The bob will have circular path at all angles , but here we need to investigate when the angle is 5°.
• When a body moves is circular motion it must have at least a radial acceleration .
• The mass is connected by a wire, the wire will have a tension . The tension should have x- and y-components.
• What the information give in problem:

• The bobs mass = 80 kg
• Length of wire = 10 m
• Angle of pendulum = 5°
• What the problem need:

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## How To Calculate The Force Of Friction

Surfaces exert a frictional force that resists sliding motions, and you need to calculate the size of this force as part of many physics problems. The amount of friction mainly depends on the normal force, which surfaces exert on the objects sitting on them, as well as the characteristics of the specific surface youre considering. For most purposes, you can use the formula:

to calculate friction, with N standing for the normal force and incorporating the characteristics of the surface.