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

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Pulling apart two interleaved phone books

The TV show Mythbusters had an episode in which they interleaved two phone books and dramatized how hard it was to pull them apart. (A long time ago, a phone book was a book that had an index of phone ...
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0answers
117 views

Particle sliding on a semisphere - solving the differential equations analytically [closed]

I have the following problem: A particle of mass $m$ is at rest at the top of a semispherical surface of radius $R$. After an impulse, it starts to slide along a meridian with speed $v_0$. The ...
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0answers
177 views

Why does the overhand knot jam but the figure-8 knot doesn't?

After tensioning a rope with an overhand knot in it, it is often very hard if not impossible to untie it; a figure-8 knot, on the other hand, still releases easily. Why is that so? Most "knot and ...
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3answers
923 views

6 wheels more efficient than 4 wheels?

Which would be easier to push in a straight line, a flat cart with 4 wheels or the same cart (and same load) with the same size wheels, but has six wheels? and why? Thanks
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2answers
122 views

Orbit in the vacuum

As the space is a vacuum and there is no friction in space, Can we assume that, if we place an object in gravity in exactly the right distance from a planet with gravity and in the right acceleration, ...
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4answers
1k views

Why do we take small steps while walking on ice?

When we walk on ice we should take small steps. Small steps ensure: a.)larger friction. b.)small friction. c.)larger normal force. d.)smaller normal force. The correct ...
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2answers
1k views

If you had two “perfectly” flat surfaces of the same material?

Let's say you had 2 nano-engineered surfaces of diamond which were as 'flat' as possible (of course considering the radii of each carbon atom in the lattice)... would there be any friction between ...
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2answers
1k views

Where does the lost energy go in a rubber band powering a rotating shaft?

Okay, I'm no physics whiz, and this has me stumped. You know those toy airplanes you can get with the rubber-band driven propellers? You twist the propeller a bunch of times, and this stores ...
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4answers
564 views

Why doesn't centrifugal force appear on an FBD for a car on a banked track?

Suppose you wish to find the max speed at which a car can travel on a banked curve of radius R and angle theta to the horizontal and coeff. of static friction mu. I don't understand the relevant ...
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3answers
198 views

Why do sand dunes, hills and mountains assume the shape they normally do?

What about something taken in a tablespoon? This shape, as I understand, could be explained by gravity, friction and similar concepts, but why the shape isn't cubical or cylindrical couldn't be ...
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1answer
1k views

Magnetic fields and friction

If I was to pass a metal object through a magnetic field would there be any friction?
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3answers
427 views

How can a vertical force cause motion at an angle?

I just started learning physics 3 days ago and am having trouble understanding what I am doing wrong. Can someone please explain my error(s)? Thanks! We have a 1kg object on a plane at a 30 degree ...
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948 views

Why are there both Static and Kinetic Friction?

When dragging an object, there is a greater start-up force than the force it takes to keep it moving. Why is this? Why are there two different values for friction?
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2answers
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Why is the damping force on a spring oscillator linearly dependent on velocity?

If you consider the damping force is friction like in: then the force should be $$F=\mu N$$ where $\mu$ is the coefficient of kinetic friction. Why then is the damping force assumed to be linearly ...
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4answers
2k views

Blocks stacked on an incline connected by rope around pulley

Two objects A and B, of masses 5 kg and 20 kg respectively, are connected by a massless string passing over a frictionless pulley at the top of an inclined plane, as shown in the figure. The ...
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2answers
2k views

Which force makes a wheel roll down the hill? What causes friction?

A wheel rolling down a hill has two axis of rotation. One is where the center or mass is and the other is the point of contact with the surface which acts as a fulcrum. I was trying to understand ...
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4answers
6k views

Static as opposed to Kinetic Friction in Rolling Motion

During analysis of rolling motion, why do we consider coefficient of friction as that of static friction and not kinetic friction?
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2answers
4k views

How does rubbing cause the transfer of electrons from one object to the other? [duplicate]

I have just learnt about electrostatics. Why would there be a transfer of electrons? Is it because of the difference of the materials (i.e. triboelectric series)? So in the case of two different ...
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2answers
63 views

Friction Between Liquid and Solid Surface

How does friction between liquid surface and solid surface differ from viscosity, the friction between liquid and liquid surfaces? Also has a word describing the process been invented or is ...
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3answers
62 views

Twisting a tightly fitting rod

Consider the task of extracting a cylindrical rod held by friction in a tightly fitting shaft. Instinctively one would tend to twist the rod around its axis while pulling. The question is, what is ...
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1answer
242 views

If friction disregard area, why the direction you drag a long object matters?

I am talking here about dry friction between solid objects, for example a ruler and a table, not anything lubricated or fluid. I noticed that with a ruler and a table for example, if you drag the ...
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1answer
99 views

Are there real life applications for Hausdorff dimensions, specifically crack formations?

I was curios about Hausdorff dimensions. They seem to neatly describe rough surfaces. So I was wondering if there are common applications of Hausdorff dimensions in things like complicated friction ...
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4answers
356 views

Friction at zero temperature?

By the fluctuation-dissipation theorem (detailed-balance for Langevin equation), $$\sigma^2 = 2 \gamma k_B T$$ where $\sigma$ is the variance of noise, $\gamma$ is a friction coefficient, $k_B$ is ...
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8answers
809 views

How would you improve braking capability on a hovercraft? [closed]

Pretty much letting my mind free-wheel. Assume a fleet of air-supported hover-craft were to replace cars/etc on the streets. Assume also that the present traffic-signals/pedestrian rules remain ...
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4answers
949 views

Why does a rotating tire use the static, rather than the dynamic coefficient of friction?

The explanation I have heard of the difference between static and dynamic friction is that static friction is stronger because bonds form when one object is put on top of another object and these have ...
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2answers
2k views

Wheel moving without sliding

Suppose we have a wheel moving on an horizontal surface, with constant velocity $v$, without sliding. This latter condition implies that the wheel rotates around its centre with angular speed $\omega ...
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3answers
1k views

Why doesn't static friction decelerate a rolling body?

I know that static friction isn't the cause of deceleration of a rolling body. But if static friction is the only force in the horizontal direction, then shouldn't there be some acceleration produced ...
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5answers
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Why would it be true that people with longer legs walk faster than ones with shorter legs?

When a person walks, the only force acting on him is the force of friction between him and the ground (neglecting air resistance and all). The magnitude of acceleration due to this force is ...
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3answers
128 views

Time reversal symmetry in the presence of friction

I was reading a paper on time reversal symmetry, and came across an example of a pendulum swinging in the presence of friction: When we consider the more realistic physical situation of a swinging ...
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1answer
81 views

Where did the energy come from?

Suppose there are two slopes. Imagine its just small slope and can be placed on your floor. One slope is made of a very smooth material and another which provides a lot of friction for example made ...
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1answer
568 views

Change in appearance of liquid drop due to gravity

A liquid drop is spherical in shape due to surface tension. But why does it appear as a vertical line under the free-fall due to gravity? (E.g. During a rain - falling raindrop) Is there a specified ...
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2answers
4k views

why making a surface “super” smooth increases the coefficient of friction?

I read that: If you take a rough surface and make it smooth, the coefficient of friction decreases. But if you make it super smooth, then the coefficient of friction increases. How come?
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2answers
1k views

Is the wind's force on a stationary object proportional to $v^2$?

I am on a boat docked at Cape Charles, VA, about 30 or 40 miles from the center of Hurricane Irene. This understandably got me thinking about the force of wind on the boat. Since air friction is ...
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1answer
560 views

Does the friction force change directions with a change in reference frame?

In a basic friction problem with Block A sliding on top of Block B, the direction of the friction force is usually explained as being simply the opposite of the direction of motion. So if Block A is ...
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2answers
285 views

Why does friction play the role of centripetal force during the turning of a car?

What makes frictional force the centripetal force of a car turning along a curve? As friction is the opposing force and acts anti-parallel so there is no component of frictional force towards the ...
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1answer
124 views

What is the physical interpretation of the linear coefficient in this ODE for projectile motion?

For the second order ODE governing the position of a projectile subject to air resistance $$ m\frac{d^2x}{dt^2} +k\frac{dx}{dt}+mg=0 \quad k>0, \> x(0)=0, \> x'(0)=V>0 $$ a ...
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2answers
158 views

Does the slip-stick phenomenon have any application?

The slip-stick phenomenon is present all around us, be it the noise of car breaks or in earthquakes. But does it have any real-life application?
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2k views

Will two trains running along the equator in opposite direction experience same wear out?

Two identical trains, at the equator start travelling round the world in opposite directions. They start together, run at the same speed and are on different tracks. Which train will wear out its ...
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2answers
2k views

What would it feel like to touch a frictionless surface

Assume there is a completely frictionless surface. Would touching such a surface be possible? If so, what would it feel to the touch?
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3answers
3k views

Does friction decrease as objects move faster against each other?

I was told that the faster two objects move against each other, the less the friction between them would be… compared to if they were moving slower. In physics class, we always use the coefficient of ...
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1answer
32 views

Why friction is not reliable for circular turns on horizontal road with high speed and sharp curve?

Why is friction not reliable for circular turn on horizontal road for centripetal force when high speed and sharp curve are involved? So banking of road has to be present to introduce a new force $N ...
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2answers
902 views

How can a train locomotive generate enough traction to pull all the coaches?

Sorry for posting what may be an obvious question but we just learning about friction at school and my teacher couldn't explain well enough to me and I would appreciate your inputs. Consider the ...
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3answers
440 views

Braking distances on a rainy road

I am curious to find the braking distance for a car on a road. In attempting to find this out, I found that the braking distance for a car (on a flat road) is $$ d = \frac{v^2}{2\mu g} $$ where ...
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4answers
1k views

Why does a tire produce more traction when sliding slightly?

It is well known in racing that driving the car on the ideal "slip angle" of the tire where it is crabbing slightly from the pointed direction produces more cornering speed than a lower slip angle or ...
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2answers
267 views

Frictional Forces

In the figure, blocks A and B have weights of 45 N and 23 N, respectively. (a) Determine the minimum weight of block C to keep A from sliding if μs between A and the table is 0.21. (b) Block C ...
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1answer
6k views

Two masses attached to a spring

I'm trying to understand the solution of the following problem. Two masses $m_{1}$ and $m_{2}$ slide freely in a horizontal frictionless track and are connected by a spring whose force constant is ...
3
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1answer
190 views

Calculating the path of a ball with spin moving across a table

A ping pong ball is rolling over a smooth (but not frictionless) table. During its travel, a clockwise spin is placed on the ball. The ball's path is changed to move to the right (in perspective from ...
3
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1answer
391 views

What is the function of the top point of a bouncing ball?

A ball is thrown away as parallel to x axis from M(0,h) point with speed V . After each jumping on x axis , it can reach half of previous height as shown in the figure.(Assume that no any air ...
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1answer
33 views

Everyday Low-Energy Atom Collider

During the shearing of metal in a machining process, what exactly is the source of the heat that is produced? I realize that the energy is coming from the work being done by the cutting tool. I am ...
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1answer
102 views

Could $\int (\ddot\phi + \mu\dot\phi^2)d\phi$ ever be negative? How to show it?

I am working on the following problem: Given a mass $m$ at rest at the base of an incline surface shaped like 1/12th of a circle with radius $R$. The mass is pulled up the incline by a rope that ...