Questions tagged [friction]

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

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294 votes
2 answers
27k views

Why do ballpoint pens write better on pages that have pages below them?

If I write on the starting page of a notebook, it will write well. But when there are few or no pages below the page where I am writing, the pen will not write well. Why does this happen?
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246 votes
8 answers
39k views

How do towels stay on hooks?

Towels (and coats) are often stored on hooks, like this: To the untrained eye, it looks like the towel will slide off from its own weight. The hook usually angles upwards slightly, but a towel does ...
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133 votes
5 answers
35k views

What does it mean for two objects to "touch"?

If you've ever been annoyingly poked by a geek, you might be familiar with the semi-nerdy obnoxious response of "I'm not actually touching you! The electrons in the atoms of my skin are just ...
109 votes
6 answers
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Why is oil a better lubricant than water?

How come mineral oil is a better lubricant than water, even though water has a lower viscosity? When two surfaces slide over each other with a gap filled with a fluid, the different layers of the ...
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76 votes
3 answers
6k views

Is there 'friction' in spacetime?

So, if all the bodies are embedded in space-time and moves through it, is there some kind of 'friction' with space time of the planets? For example, the Earth suffers friction when moving near the sun ...
67 votes
2 answers
9k views

What explanations are there for a rug steadily creeping at about a millimeter/day rate across a room? [closed]

I have bought a handmade rug of size 1.5 $\times$ 2m. About 1-2 weeks ago I noticed the rug was not in the center of my room and it had moved a bit. I thought maybe because I walked on it, it has ...
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60 votes
6 answers
9k views

Can a Skydiver Land On a Large Slide and Survive?

Please forgive my lack of artistic ability, but here's my question: Consider that a skydiver, without using his parachute, were to fall exactly parallel to a giant curved slide that starts at $90\,^\...
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52 votes
2 answers
13k views

Why is the equation for friction so simple?

The general equation for the force of friction (static or kinetic) is $F_f = \mu * F_N$, where $F_f$ is the force of friction and $\mu$ is the coefficient of friction (its value is dependent upon the ...
45 votes
9 answers
12k views

What will happen to a ball kept on a frictionless inclined plane?

I was wondering about this question since I learned about rolling motion in the chapter on rotational mechanics. I was unable to come to a solid conclusion due to the reasons mentioned below. The ...
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44 votes
1 answer
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Why are dishwasher washed glasses "squeaky clean"?

They seem to have increased friction after going through a dishwasher. The unpleasant (to me) squeaky feel is probably slip-stick friction exciting resonance in the glassware. But why? What has ...
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40 votes
6 answers
8k views

How can the Earth keep spinning with a liquid core?

In regards to the 'conservation of angular momentum' being the explanation of why celestial objects spin... If you fill a ball or any other container with a liquid and try to spin it, you will not ...
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39 votes
9 answers
14k views

Why do bikes hardly ever skid while braking with the front wheel?

When abruptly braking with the rear wheel on a bike, it tends to skid pretty easily. Doing the same with the front wheel is a very different experience. Instead of skidding, the bike lifts the rear ...
35 votes
3 answers
6k views

Push a Boeing 737 on ice: Did this guy have a chance? [closed]

In this video an airport worker (in blue) tries to prevent a Boeing 737 from sliding on ice in heavy winds: Did he even have a chance? On one side of the argument, the airplane is sliding due to the ...
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33 votes
4 answers
12k views

Why do computers generate heat?

Computers generate heat when they work. Is it a result of information processing or friction (resistance)? Are these just different ways to describe the same thing? Or does some definite part of the ...
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32 votes
8 answers
7k views

Why does twisting a cork make it easier to remove from a bottle?

When we want to remove a cork from a bottle first we turn the cork. Turning in one direction makes it easier to remove in the axial direction. Does anyone know something more about this?
31 votes
6 answers
35k views

Why does a tire need to be filled with air?

The Mini 4WD's tires aren't full of air, and it can run. Also, the tank doesn't have tires with air. So, the question is: why do real cars on the road need to be filled with air? What is the idea ...
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31 votes
6 answers
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Can I survive a free fall using a ramp and a rope?

Can I survive a free fall by carrying a very light and resistant ramp using a rope? Note: lets assume the ramp is a little bit heavier at the bottom and I am very skilled at making it always land ...
29 votes
3 answers
3k views

Why doesn't a fly fall off the wall?

Pretty simple question, but not an obvious answer at least not to me. I mean you can't just place a dead fly on the wall and expect it to stay there, he will fall off due to gravity. At first I ...
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29 votes
5 answers
3k views

How is it possible for the same force to do different amounts of work in two different inertial frames?

Consider an object which has been given a speed $v$ on a rough horizontal surface. As time passes, the object covers a distance $l$ until it stops because of friction. Now, Initial kinetic energy = $\...
28 votes
2 answers
8k views

Lagrangian and Hamiltonian EOM with dissipative force

I am trying to write the Lagrangian and Hamiltonian for the forced Harmonic oscillator before quantizing it to get to the quantum picture. For EOM $$m\ddot{q}+\beta\dot{q}+kq=f(t),$$ I write the ...
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28 votes
1 answer
2k views

Is gecko-like friction Coulombic? What is the highest known Coulombic $\mu_s$ for any combination of surfaces?

Materials with large coefficients of static friction would be cool and useful. Rubber on rough surfaces typically has $\mu_s\sim1-2$. When people talk about examples with very high friction, often ...
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27 votes
6 answers
10k views

What force enables us to walk? Friction or normal reaction?

I know that this question has been asked here before, but I am a little bit confused with all the answers. So when we move, we apply force on the ground in the backward direction. So, is the ground ...
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27 votes
5 answers
21k views

Does a car consume more fuel when it's raining?

Yesterday my wife asked me that question, and I couldn't answer. Consider a car, in a sunny day, and that is consumes x gallons per mile. Considering that everything is equal, except that it's ...
25 votes
14 answers
6k views

What makes a wheel spin?

I don't fully grasp what makes a wheel much easier to move than to push a solid block. The pressure at the point of contact between a wheel and the ground must be pretty enormous compared to the ...
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25 votes
1 answer
4k views

What determines the angle of the cushion on a pool table?

If you look at the cushions (bumpers) on a pool table, you'll see that they're not vertical. They're tilted inwards. About 10 years ago, I came across a physics exam in which one of the problems ...
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24 votes
14 answers
26k views

Is it possible to walk in a friction-less world?

Is it possible to walk in a frictionless world. I think you won't be able to walk because walking depends on friction acting on your feet. I think about it like an ice rink because when you try to ...
24 votes
3 answers
2k views

Why do we tap on cardboard to see magnetic field lines?

If we sprinkle iron particles on a cardboard where a bag magnet is kept and tap the board gently then the particles get arranged in a way that they look like field lines. But I am confused why do we ...
24 votes
5 answers
11k views

Why are a motorcycle's front brakes more effective than back?

I've noticed that when I apply the front brakes on my bike it stops quite quickly. If I apply the back brakes at the same speed, it skids rather than stopping quickly. Why?
24 votes
5 answers
68k views

What is the cause of rolling friction? & why is it less than sliding friction?

Rolling friction is the resistance to motion experienced by a body when it rolls upon another. It is much less than sliding friction for same pair of bodies. When one body rolls upon another, there is ...
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24 votes
6 answers
5k views

Conical train wheels

I've been reading about how the conical shape of train wheels helps trains round turns without a differential. For those who are unfamiliar with the idea, the conical shape allows the wheels to shift ...
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23 votes
6 answers
5k views

Why does low tire pressure increase friction?

I've always thought that it was because the frictional force on the tire was increased due to the bulging of the tires increasing the surface area in contact with the road. However, a colleague of ...
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23 votes
6 answers
89k views

Can the coefficient of static friction be less than that of kinetic friction?

I was recently wondering what would happen if the force sliding two surfaces against each other were somehow weaker than kinetic friction but stronger than static friction. Since the sliding force is ...
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23 votes
2 answers
579 views

How many molecules rub off when I press a key?

I have a lot of questions below but my overarching questions are: Do surfaces rubbing lightly together always strip molecules off of each other? and How can we model that? Clearly the answer to the ...
22 votes
6 answers
5k views

Would you feel Centrifugal Force without Friction?

This question arose from my sci-fi discussions with my friend. It concerns artificial gravity through centrifugal Force. Partly inspired by the Artificial Gravity created on the Hermes ship from the ...
22 votes
4 answers
4k views

What determines the top speed in ice skating?

I was watching a hockey skating competition. The best skaters are able to accelerate quickly and turn without losing much speed; however, most people have similar top speed around 20-25 mph. What is ...
22 votes
4 answers
17k views

Dependence of Friction on Area

Is friction really independent of area? The friction force, $f_s = \mu_s N$. The equation says that friction only depends on the normal force, which is $ N = W = mg$, and nature of sliding surface, ...
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21 votes
5 answers
7k views

Why do bullets shoot through water but not through sand?

There are a few questions only on this site about this but none of them answer my question. Can cannonballs go through water? Why does a bullet bounce off water? I find it hard to understand why ...
21 votes
2 answers
33k views

Why do people recommend wider tyres in car for better road grip?

Tyre companies boast of their wider tires for better grip on road. Also, the F1 cars have broad tires for better grip. But as far as I know Friction does not depend on the surface area of contact ...
20 votes
3 answers
2k views

Why does all motion in a rigid body cease at once?

I was reading through a book that presented the problem: A disgruntled hockey player throws a hockey stick along the ice. It rotates about its center of mass as it slides along and is eventually ...
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19 votes
6 answers
12k views

Why doesn't the road lose its thickness to the tyre?

From this source, on average a rubber tyre loses $2$ atoms thickness per revolution due to the friction with the road. Do these atoms/molecules that were peeled off the tyre get absorbed by the ...
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19 votes
6 answers
6k views

Is there a quasistatic process that is not reversible?

I have seen several questions and good answers on the link between reversible and quasistatic processes, such as here or here. However, these questions only adress one side of the problem : a ...
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19 votes
2 answers
65k views

What role does static friction force play for a rolling object? How can I know what direction it points?

Fundamentally, what does a friction force do for a rolling object? I am very confused by the way my textbook explains it. In my textbook , it says: A wheel rolling on a horizontal flat surface at a ...
19 votes
2 answers
2k views

How hot does the tip of a pencil get while writing?

When writing with a pencil, there seems to be quite a lot of friction - which seems like it would induce heat. How hot would the tip of a #2 pencil get writing on normal copy paper?
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18 votes
6 answers
11k views

In car driving, why does wheel slipping cause loss of control?

When driving a car on ice, there is a danger of slipping, thereby losing control of the car. I understand that slipping means that as the wheels rotate, their circumference covers a total distance ...
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18 votes
4 answers
7k views

Will a pure rolling cylinder stop on a rough surface? [closed]

Will a disc or cylinder (rigid body) executing pure rolling on a rough surface stop, neglecting air drag and other heat losses and rolling friction but not static and kinetic friction? If yes, due to ...
18 votes
5 answers
4k views

How can friction do no work in case of pure rolling?

I have read various answers, on PSE and elsewhere, and most of them explain that the point of contact of the rolling object undergoes no instantaneous displacement in the direction of friction, I ...
18 votes
5 answers
7k views

How does a car turn without any skidding?

The rear wheels of a car always face in the direction the car is moving. The front wheels are able to turn left or right and thus can point in the direction the car is moving towards. What I don't ...
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18 votes
7 answers
27k views

Does ABS shorten stopping distance of a car?

ABS, from German Antiblockiersystem, is a device put in almost every new automobile. The web has lots of explanations about the system, how it works, but I don't understand how it shortens the way of ...
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18 votes
5 answers
132k views

Block on a block problem, with friction

Consider two blocks, one on top of the other on a frictionless table, with masses $m_1$ and $m_2$ respectively. There is appreciable friction between the blocks, with coefficients $\mu_s$ and $\mu_k$ ...
17 votes
6 answers
7k views

Can I push something standing on a frictionless floor?

Suppose I stand on a friction less floor, and another object of finite nonzero mass stand in front of me. Can I push the mass, so that it has a nonzero acceleration? Also, where does this force arise, ...
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