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

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Does the force of kinetic friction increase with the relative speed of the objects involved? If not, why not?

Does the force of kinetic friction increase with the relative speed of the objects involved? I have heard and read that the answer is no. This is counter intuitive, and is a big part of why the ...
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2answers
999 views

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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3answers
357 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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821 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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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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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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1answer
93 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
320 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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1answer
165 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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8answers
720 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
886 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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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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76 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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494 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
981 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
514 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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3answers
98 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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3answers
166 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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149 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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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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3answers
2k 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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2answers
761 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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777 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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407 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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216 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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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 ...
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1answer
173 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 ...
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1answer
337 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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5answers
2k views

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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4answers
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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
96 views

Consider a horizontal surface with or without friction. Ideally, will a wheel rolling without slipping roll forever in both cases?

Suppose a wheel is rolling smoothly on a horizontal plane i.e., it is rolling without slipping. Now let's take the two cases of the horizontal plane: It has friction It is frictionless In the ...
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3answers
228 views

How can a block which is not receiving the direct force have a greater acceleration?

I solved it like this: $$F(\text{st max})=5\text{ N}$$ For the top block, $$\begin{align} 6\text{ N} - 5\text{ N} &= 1a \\ a &= 1\ \mathrm{m/s^2} \end{align}$$ For the lower block, the ...
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923 views

Why does friction cause a car to turn?

I've had a lot of difficulty conceptually understanding the physics of how a car turns on an unbanked curve, so I'm hoping you could help me out. When a car is moving in uniform circular motion, we ...
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468 views

A block on a wedge

The system is as follows - Friction exists only between the 2 blocks. I am trying to find out the accelerations of $m_1$ and $m_2$. Let $a_2$ be acceleration of $m_2$, and $a_x$ and $a_y$ be the ...
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1answer
715 views

Angular momentum after elastic collision

If two balls collide (elastically) and there is no friction between them, will their angular momentum change after the collision?
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152 views

Friction on roads

I have a question with which I am having trouble. A 71m radius curve is banked for a design speed of 91km/h. Given a coefficient of static friction of 0.32, what is the range of speeds in which a car ...
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Conservation of angular momentum in helicopter

I have a small RC-controlled toy helicopter with removable tail rotor. Suppose I remove the tail rotor, hold the tail with my hand, start the rotor until it moves with constant angular velocity and ...
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439 views

Strict general mathematical definition of drag

Is there a formal definition of drag, say, as some surface integral of normal and shear forces? There seem to be a lot of formulas for specific cases, but is there a general one? I need to accurately ...
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2answers
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Does a car use friction to move?

When a car's engine injects fuel into the cylinder chambers, the reaction creates a force that generates rotational momentum to the shaft and over the transmission, it translates that power to the ...
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291 views

Does air resistance ever slow a particle down to zero velocity?

If a particle moves in a place with air resistance (but no other forces), will it ever reach a zero velocity in finite time? The air resistance is proportional to some power of velocity - $v^\alpha$, ...
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1answer
781 views

Rope wrapped around a cylinder

If a rope is wrapped aound a cylinder what is the relationship between the amount of wrap and the ability to resist slipping off of the cylinder? An example would be if I had a 180 degree wrap and ...
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0answers
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How to get rotation speed after disk-disk collision?

Assume two circular disks A and B collide. They have both initial linear momentum and angular momentum. If their surface has no friction, their angular velocity does not change after collision, so I ...
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0answers
39 views

How much weight is lifted from each side? [closed]

I don't know the math to do this, so I am asking here if someone can work this out with all of the details I'm providing. Total mass EST.: 2,400 lbs. Length from front to back: 14 feet 6 inches. ...
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1answer
125 views

Sliding ruler on table top

I've got a standard foot-long flat plastic ruler (about an inch wide) and a desk with a smooth formica-like surface. When idly passing time reading on the computer, I will pick up one side of the ...
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4answers
208 views

Would a three wheeled vehicle be faster than a four wheeled vehicle of the same weight?

If I have a four wheeled vehicle (small wooden block with metal nail axles and plastic wheels) and apply a force X to it, would it be made faster by keeping one wheel off the ground in order to reduce ...
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5answers
360 views

Ball rolling into a bowl - where is its maximum KE (speed)… given there is friction. See diagram

Please examine this diagram and answer the apparently trivial questions. I am particularly interested in reasoned answers for part (a)(ii) - where is the maximum Kinetic energy? I say it is at B ...
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3answers
892 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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Physics behind Wheel Slipping

Lets say that I'm in a car and I apply full acceleration suddenly. Now, the wheels would slip and hence the car doesn't displace much. But If I start with some constant acceleration, slipping doesn't ...
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Euler-Lagrange equations and friction forces

We can derive Lagrange equations supposing that the virtual work of a system is zero. $$\delta W=\sum_i (\mathbf{F}_i-\dot {\mathbf{p}_i})\delta \mathbf{r}_i=\sum_i ...