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1
vote
1answer
47 views

Opening a bottle cap

How exactly is a bottle cap opened/closed? To open/close one, it needs to be rotated and simultaneously translated upwards/downwards for it to move up/down its thread and not be translated right or ...
1
vote
1answer
98 views

How do knife blades become dull?

Knives are normally used to cut softer objects. So the edge of the knifes blade is harder than the substance it cuts through. A blades geometry is more complex, but let's simplify it to the blade ...
2
votes
4answers
936 views

Why we can't write in air? [closed]

Why we always require a surface to write something? Why we can't write in air? I think that it is due to friction but I am not sure about it. Edit As per helpful comments and responses, I think ...
4
votes
2answers
133 views

What opposes a smooth motion of a rubber eraser on a glass surface?

A metal block smoothly moves on a glass surface. But a rubber eraser doesn't move very smoothly on a glass surface. In each of the cases, the surfaces are smooth at the macroscopic scale. If the ...
0
votes
0answers
55 views

Derivation of friction in interleaved phonebooks

Trying to understand the simple model in https://arxiv.org/abs/1508.03290, describing the friction between the pages of two interleaved phonebooks. Specifically I don't see how to get Eq. 1. Here's ...
1
vote
0answers
47 views

Does ABS increase the breaking distance of a car? [closed]

Question: Can an ABS (Anti-lock Braking System) instead of decreasing the breaking distance actually increase it? If yes, is this its general behaviour, or only in specific circumstances? Wikipedia ...
39
votes
9answers
12k 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 ...
8
votes
2answers
370 views

Sharpening Scissors with aluminium foil

There are lots of websites 1, 2,3 that claim you can sharpen scissors by cutting aluminium foil. Does this work? What would be the cause of this?
0
votes
2answers
108 views

When you have engine at idle and turn your car, where does the kinetic energy go?

When you turn the front wheels to the right for example, your car will tend to continue in its original forward direction. However, there is friction between the wheel and the ground that prevents it ...
1
vote
1answer
187 views

Why trains are not heavy? [closed]

I have seen a video on youtube where Feynman explains that engines of trains are heavy to compensate for the fact that steel has a low coefficient of friction. But, whereas this seems plausible for ...
-2
votes
1answer
766 views

Physics/forces involved when separating two 5 gallon buckets

So a friend jokingly said "there's no force in the universe stronger than two 5 gallon buckets that are stick together." And I thought that this has to have a wonderfully complex and scientific ...
0
votes
3answers
87 views

If friction acts on car all time, why is it not accelerating forever? [closed]

In the first gear, slowly releasing my clutch i push the gas pedal to the maximum torque level, say at 2000 rpm. Now as the engine torque is acting on the wheel, friction helps the car to accelerate. ...
1
vote
3answers
153 views

Why doesn't a new ball-point pen write as smoothly as one being written for a little?

Why doesn't a new ball-point pen write as smoothly as one being written for a little? You will say that the friction is more first up.Then why is that so?
-1
votes
2answers
877 views

Conservation of energy when we drive a car

When we drive a car, we use gasoline as the source of energy. When we arrive at the destination, we lose some of the gasoline, used to move the car from one point to another. Then how energy is ...
228
votes
8answers
35k 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 ...
0
votes
1answer
90 views

Explain why a stationary object on an inclined plane may start moving after a random time? [duplicate]

An object (such as a mug of coffee, expensive phone, laptop) is placed on an inclined plane and remains stationary due to friction. After an interval (observed as random) it will begin to move (and ...
1
vote
2answers
182 views

Running vs. walking in slippery condition

We are experiencing warmer weather than normal, which is causing the snow to melt and re-freeze daily. This has led to very slippery conditions. A few years ago, I was running in similar conditions, ...
67
votes
2answers
7k 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 ...
-1
votes
1answer
99 views

What happens when we turn pages with wet fingers

Most of the people touch their tongues with fingers and then turn pages. Why do pages don't turn sometimes with dry hands? And what happens when we turn them with wet hands? If water decreases the ...
266
votes
2answers
23k 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?
2
votes
3answers
85 views

Theories of bolt heating (I)

Besides the common way of loosening a bolt by heating its nut (or whatever else it's screwed into), there are some interesting theories of how heating the bolt itself helps, at least sometimes. One ...
0
votes
2answers
102 views

Can a scooter detect the friction offered by the ground? [closed]

If the accelerator changes a body's velocity and turning it and bringing it a fixed point results in a constant velocity, this means that the force being exerted is equal to the kinetic frictional ...
1
vote
1answer
1k views

What slows down a fidget spinner more: air resistance, or friction from the bearing?

So "fidget spinners" are now massively popular. I got one, and it occurred to me that I'm not sure which force is more important in slowing them: friction in the bearing, or air resistance acting on ...
0
votes
1answer
79 views

Bicycles: What determines braking power? [closed]

Today I had an argument with a guy over what the main source of braking power in a bike comes from. (We define "braking power" informally as the ability of a bike to stop quickly.) He said that the ...
2
votes
4answers
2k views

Friction on tyres

The force of friction is directly proportional to area of contact. But then why do the tyres of trucks and other large vehicles have big gaps in them? It reduces the area of contact so frictional ...
4
votes
4answers
939 views

Why is it so much easier to fall when walking down a slope?

When I walk uphill on an icey road, I almost never slip/fall. But if I walk downhill or even on a relatively flat road, I slip/fall frequently. What is the physics reason behind this, and are there ...
4
votes
4answers
563 views

Why is clothes-wet skin friction coefficient higher than clothes-dry skin?

Always when I'm wet after bathing and try to dress, or when I try to put a wet sock in my (dry or wet) feet, the friction skin-cloth is very high compared to both dry. Why does water increase the ...
18
votes
6answers
9k 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 ...
3
votes
2answers
3k views

Why do racing tires (slicks) provide more traction with the road?

Google: By eliminating any grooves cut into the tread, such tires provide the largest possible contact patch to the road, and maximize traction for any given tire dimension. My understanding is that ...
98
votes
6answers
21k views

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 ...
16
votes
2answers
619 views

Why does temperature change the friction coefficient of my stovetop?

I have a Ceran cooking field at home, it's a glass-ceramic surface with heating coils embedded beneath. When I slide a pan around there's much more friction on a hot plate than on a cool one. Why? ...
2
votes
2answers
2k views

Why do tires with low air pressure experience more friction?

How does tyre pressure affect the frictional force on a tyre even though friction is independent of area of contact? And how does one analyze or calculate this friction?
35
votes
3answers
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 ...
2
votes
1answer
6k views

Why do bowlers rub the ball before bowling in a cricket match?

Why do bowlers rub the ball before bowling in a cricket match? What is the science behind it? Is it because of friction?
3
votes
1answer
3k views

How does a bowl of hot water move by itself?

I think everyone should have seen a bowl of hot water moving by itself on a flat surface such as glass(seems like it is moving by itself but maybe there are some external force applied to it when it ...
42
votes
1answer
6k views

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 ...
24
votes
5answers
9k 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?
22
votes
1answer
473 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 ...
2
votes
10answers
5k views

Who does work while walking?

While walking the work done by friction is zero. But who does the work, actually? How someone is getting displaced? This situation also arises when someone climbs without slipping or is climbing a ...
0
votes
1answer
660 views

How do whitening toothbrushes work?

Certain "whitening" toothbrushes are sold and I was wondering about the mechanisms behind the tooth whitening process. I suspect this is related to the shape and arrangement of the fibres, probably ...
1
vote
2answers
589 views

Does distance traveled by a vehicle after its engine has been switched off depend on its mass at all?

A vehicle moving with some velocity on a rough horizontal road finally comes to rest after its engine has been turned off. Intuitively, it seems a vehicle with greater mass would stop first because it ...
0
votes
1answer
274 views

Why is mud muddy?

How to explain properties of mixture of sand with water? Why is it so coherent and slippery at the same time? Is it due to hydrogen bonds? Why is mud of smaller grains more slippery and incoherent ...
2
votes
1answer
1k views

Accelerate the car by static friction

I asked this question about friction and slip ratio and now I still don't understand it Why friction is zero when wheel slip is zero? As the below graph of wheel friction vs slip ratio shows that in ...
2
votes
3answers
2k views

Why friction is zero when wheel slip is zero? [duplicate]

From most graph, when the tire doesn't slip, then the friction is zero, for example see the below image Why there is no friction when there is no slip? As the car stand still on slope, there is no ...
1
vote
1answer
854 views

Why does a car bonnet (hood) rise when you connect the clutch with a brake on?

Is the rotational force to overcome the brakes moved to the opposite effect of moving the car chassis, until the brake is released?
2
votes
3answers
3k views

Does the mass of a car frame has any effect on its horsepower?

I want to know whether decreasing the mass of the frame of a car will increase its horsepower. From what I understand horsepower is a measure of the car's ability to transport load, and decreasing the ...
16
votes
6answers
20k 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 ...
8
votes
5answers
10k 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 answer ...
25
votes
5answers
15k 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 ...
18
votes
2answers
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?