The resistance a surface or object encounters when moving over another.

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659 views

Does anti-lock braking system (ABS) perform reverse rotation sometimes?

In cartoons we can see, how vehicles brake by rotating wheels reverse. Will this be helpful sometimes in real situations? I know that the main tactics of ABS is to maintain tractive contact. But may ...
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2answers
987 views

$\gamma$ in Newton's Second Law of Motion in Differential Form

I am teaching myself Differential Equations from a website. In the website I am up to Direction Fields and an example of a differential equation is Newton's Second Law of Motion. It is written on the ...
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1answer
896 views

Friction force and contact area [duplicate]

It's usually stated that the friction force is independent of the area of contact (Amontons' Second Law). I've always thought that this shouldn't be true, because the atraction between molecules ...
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2answers
4k views

Physics behind Water drops during falling from a tap

what is physics behind Water drops during falling from a tap. water drop animation A drop or droplet is a small column of liquid, bounded completely or almost completely by free surfaces. Why Water ...
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1answer
203 views

Is energy “destroyed” when walking?

Conservation of energy states energy can't be destroyed, but isn't energy used up when walking in a straight line? If your not walking up a slope, kinetic energy isn't converted to gravitational ...
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2answers
616 views

Friction between air and a tube

I would like to know how I could estimate the friction caused by air flowing at a speed of 1000 km/h in a tube. The tube could be made out of any material, which makes it possible to calculate, ...
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2answers
39 views

Free body diagram for two masses on inclined plane with frictions

I'm a bit confused about free body diagrams on inclined planes with frictions. Consider the situation in the picture, where $A$ and $B$ slide togheter on a inclined plane and I want to find a force ...
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1answer
65 views

Compression vs. Friction - what happens when space objects enter earth's atmosphere

When reading about what happens when cosmic debris enters the earth's atmosphere, some sources say friction, others say compression. For example: On space.com it says: Meteor showers occur when ...
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2answers
37 views

If two very small and smooth particles collide at perfect right angles, is there friction?

If two perfectly round particles collide at perfect right angles, is there friction between them? If so, Is the friction in the form of heat (average kinetic motion), because if it is, where is this ...
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3answers
153 views

When does normal force equal to $mg$?

Can someone once and for all explain when does normal force equal to mg? I know for sure that when there is no friction, normal force will be equal to mg. But, i encountered some questions when there ...
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1answer
70 views

Measure ball's acceleration down inclined plane

If I am asked to devise an experiment to find an expression for the acceleration of a uniform sphere (ball bearing) rolling down an inclined plane, as a function of the angle of incline. Hence deduce ...
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1answer
42 views

Mismatch between underdamped and critically damped solutions

If you have a harmonic oscillator with damping $D$ (e.g. small angle pendulum) $$\ddot{\theta}+D\dot{\theta} + \theta=0$$ then the solution I get in the underdamped case ($D^2-4<0$) is: ...
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4answers
108 views

Is cause of this equilibrium - tension or friction?

This is a very odd problem which I have. As you can see in the diagram, the string is taut. So, if there was no friction you could clearly say that tension is balancing it or if there was no tension ...
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2answers
100 views

Is friction a function of surface area? What is the microscopic workings of friction?

I know the friction is given by the following equation $$\mu F_N=F_f$$ which tells me friction is independent of surface area, but how do I characterize it as such if I want to add surface area into ...
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1answer
97 views

Why friction force peak just before the object moving?

This diagram shows the amplitude of friction force of a typical contact-surface object. The friction force increases as we apply an internal force until it reach a maximum value just right before ...
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2answers
52 views

Some confusion pertaining to direction of static friction on stationary object

Consider a stationary object of mass $m$ on a horizontal table. Since the object does not move relative to table, $f_s=0$. So it seems that we first consider $mg$ and normal reaction force,$N$ ...
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1answer
88 views

Does a propeller being pushed through the air have more friction if free to spin?

I just passed a boat being pulled on a trailer and noticed the propeller spinning in the wind. I began considering the possibility that a propeller free to spin might cause less friction against the ...
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5answers
208 views

Why does solving $\mu mg = m \frac{v^2}{r}$ give the *max* possible velocity?

So here is the standard problem setup of a car turning on an unbanked road: A 1000 kg car is going around a curve with radius 30 meters. If the coefficient of friction between the car's tires ...
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5answers
2k views

How can static friction do work?

By definition, the work done by a force is $W = F\cdot d$, so how can static friction do work? Can this force move the body a distance of $75~\text{m}$?
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1answer
83 views

Running Euler's disk in a superfluid

I was considering the toy Euler's Disk, a video can be found here: http://www.youtube.com/watch?v=mVl2CBG_h2s I was interested in understanding the behavior of the disk particularly in vacuum and in ...
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1answer
375 views

Rate of Temperature Change due to Heat addition

I might be wrong but I will give a little background leading to my question. I am trying to calculate the heat generation in the advection-diffusion equation for heat generation due to friction by ...
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3answers
9k views

If mass is added to a toy car does it affect its speed making it faster

If mass is added to a toy car (29.7g) and dropped down a wooden ramp would it affect its speed making it go faster? I know friction comes in to play to, so if you could give me an answer or an ...
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1answer
197 views

What force counteracts friction when a block is pulled?

Firstly, I understand and apologize that this is more of a physics question than a math question. I noticed that when I pulled a book out from under a pack of gum, the gum stayed largely in place (it ...
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1answer
41 views

Clarification what exactly this question wants regarding force [closed]

I would like to ask you if the question asked What is the minimum force parallel to the plane, which can be prevent the block from slipping down the plane? I just did the calculation and and ...
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1answer
1k views

Mechanics question - ladder leaning against a wall

I am struggling with part a) of this question: Here is the solution: In part a) they prove that $F \leq \mu R$ is false for this system. So as $F$ is neither less than nor equal to $\mu R$ it ...
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3answers
270 views

Energy expended in moving point charge in E field. Having trouble understanding an excerpt from E&M textbook

To move charge from one point to another in an electric field, the force which we must apply is equal and opposite to the force due to the field. (Quoted from Engineering Electromagnetics by ...
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1answer
1k views

Finding friction forces of stacked boxes on a table

Consider the following system. The given friction coefficients are for static. Let $g=10$ (meter per square second). If the $F(t)=10t$, for example, determine the friction forces $f_{AB}(t)$ ...
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4answers
661 views

How long does it take for an electric car to go from 0 to 60 mph?

I found the freefall motion equation which describes terminal velocity of a falling body, but I can't find a similar equation for a vehicle subject to constant traction force, so I tried determining ...
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2answers
352 views

Direction of friction for object that rolls with slipping

Let's say you hit a cue ball with a pool stick that causes an impulse. If the pool stick hits the ball above the ball's center of mass, is the direction of friction different than if the pool stick ...
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1answer
721 views

Using Lagrange's Equations with Generalized forces

I am a bit confused on how this works. For instance if I wanted to look at an object moving in 2 dimensions only subject to gravity (and assuming that the potential is just mgy), I get that my ...
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1answer
136 views

Is the trajectory of the Moon around the Earth stable? [duplicate]

I understand how mathematically is possible to have one object with elliptical or circular orbit around another object in space. so can I think of it as a limit cycle? If yes, then is it stable or ...
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2answers
6k views

Finding max height of a mass launched by a spring?

I have the following problem on my homework. The actual problem has numbers, but I figure using symbolic notation will help me understand the concept in the long run. A block of mass $M$ is launched ...
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1answer
819 views

Newtons Cradle, Collision Theory

It has come to the point in my computing program now where I have 5 swinging pendulums that are all modified at once by slider values. These values are drawn onto the from and passed through the class ...
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3answers
2k views

Resistive force proportional to velocity

Find the displacement and velocity of horizontal motion in a medium in which the retarding force is proportional to the velocity. I kind of understand how to do this problem. We know that the ...
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1answer
5k views

Calculating the frictional force

Here's my problem and the work I've done. The time is already past for me to submit the answer, but I want to know where I went wrong and why I was wrong. The 2-kg box slides down a vertical wall ...
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1answer
372 views

Circular motion question

(Q) Find the maximum speed at which a truck can safely travel without toppling over, on a curve of radius 250m. The height of the centre of gravity of the truck above the ground is 1.5m and the ...
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2answers
2k views

Is the newton's second law for a body experiencing a frictional force, relative to the surface in contact?

Let us consider a routine mechanics problem.A block of $ 10kg $ rests on another block of $ 2kg $ on a frictionless table.Let $ \mu = 0.2 $ be the coefficient of friction(let's neglect the difference ...
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1answer
259 views

Why is this classical system seemingly non-deterministic?

So, I was solving this problem1 and I realized that the system given seems to be non-deterministic when analysed with classical laws. The situation is thus: A rope is wrapped for an angle of ...
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2answers
4k views

Slowdown rate of rotating body due to friction force [closed]

This isn't a homework question, but it might as well be. The problem I have been pondering is: If a disc (or children's roundabout if you like), of radius r, mass m, is spun around it's center ...
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1answer
1k views

Friction on a conveyor belt

I was surfing through an Olympiad paper and I was caught with this question. A block of mass 1 kg is stationary with respect to a conveyor belt that is accelerating with $1\, \tfrac{m}{s^2}$ ...
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1answer
344 views

calculating work done by friction

I want to calculate the work done by friction if the length $L$ of uniform rope on the table slides off. There is friction between the cord and the table with coefficient of kinetic friction $\mu_k$. ...
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2answers
2k views

Can a simple pendulum be considered a simple harmonic oscillator?

Is the motion of a simple pendulum, a simple harmonic motion? It stops vibrating after sometime.
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912 views

Ropes and Pulleys - Really unintuitive answer

I usually don't want to do this, but please go to this link, the solution is too big to post it here http://engineering.union.edu/~curreyj/MER-201_files/Exam2_2_26_09_Solution.pdf And go to page 5 ...
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1answer
3k views

Two problems with free body diagrams. Contradictions (solutions are provided)

This problem is similar, but also different question from my previous question. They are both unfortunately long. Problem/Solution #1 ! ! Quick Concept Check a) Could someone briefly explain to me ...
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534 views

Linear motion with and without Friction

Could we still use Newtonian mechanics in a frictionless world?
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1answer
49 views

What makes cart with a moving object in it gain speed (no friction anywhere)?

I would like to understand what makes the cart below the moving object move. There is no friction between any of the objects. The cart is moving therefore there is force applied to it. The only force ...
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4answers
71 views

Negative friction force, positive normal force

I realize that formulas don't always tell the whole story, but there seems to be some information missing from the equation: $F_f=\mu F_N$ Imagine we say up and right is positive. Then if an object ...
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1answer
27 views

How far will the key slide? [closed]

A person tosses his car keys on a shelf with an initial velocity of $2\:\mathrm{m/s}$. How far will the keys slide if the coefficient of kinetic friction between the surfaces is $0.3$? How would you ...
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1answer
31 views

Does an object reversing direction experience static friction?

I know that there is kinetic friction, experienced by an object in motion, and static friction, experienced by a stationary object put into motion. Take an object that is pushed, this push makes the ...
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2answers
101 views

Why friction between two smooth surfaces is high? [duplicate]

If we place two smooth surface one over the other why friction increases or becomes high ?