New answers tagged

2

Both the tire and the pavement wear from the contact between the two. The road will take significantly more damage if the tire has rocks stuck in the treads, but even in a "pure system" of perfectly clean rubber tires, the road suffers erosion just like everything else. The folks who commented on the hardness or density of the pavement are right, but ...


0

Kirchhoff's law of thermal radiation says that the absorptivity and emissivity for a given wavelength are equal, so the silvery surface would emit less infra-red radiation.


62

Anyone who has lived near a major thoroughfare knows that tire wear creates rubber dust that gets spread around everywhere. In some parts of Los Angeles, the residents have to hose off the sidewalks every day or so in order to prevent that dust from being tracked into their homes. Some of it also gets friction-welded into the surface of the road itself, ...


15

I believe it has to do with the hardness of the tire vs the road. Hardness is a measure of resistance to wear and the material of a paved road is generally harder than the material of a tire. So the tire will wear before the road with a net transfer of material from the tire to the road. Hope this helps.


0

You miss the dynamical part of the story. With that considered, I would like to say to store it up right because when you open it, it is up right. If you store it horizontally, the shake of bottle will release more gas if it is stored horizontally in the first place.


2

Three factors come into play here. One is that the solubility of gases in water tends to decrease with increased temperature and with decreased pressure. This is why it's a bad idea to open a warm soda bottle. Cool it first. This is also the case for nitrogen and oxygen, the main constituents of the atmosphere), and also chlorine, which is widely used to ...


2

The problem is simply that we can't move our arms quickly enough. We have the strength- a lever-action airgun shows that the equivalent of a good shove is enough to fire a pellet- but we don't have the speed.


4

As The Photon wrote in a comment, the issue is that you have to accelerate your hand as well. So while the 4.4g bullet only needs 304N to accelerate (by your numbers in the comments), your 400g hand has to reach the same speeds on roughly the same distances, requiring on the order of 30000N, well outside the range of the human body. You may, however, be ...


0

If you could accelerate the gun to the same speed it has right after the shot, you could use it to hit the bullet and make it fly at the right speed. However, this speed is still very large and you cannot use your shoulder hand system to do it. Our body can stop a gun moving at such speed but cannot bring it back to it.


0

In airsoft and in other real life scenarios, the reynolds number is low enought that the flow is laminar both on the upper and low side of the ball. So backspin give lift. Above critical reynold number the flow is turbolent on both sides so again backspin give lift. In the first image the sum of the ball speed plus the backspin give enought speed for the ...


41

In an unopened 2L polyethylene terephathalate (PETE) bottle of soda the primary loss of CO2 is by diffusion of the CO2 through the walls of the plastic bottle. If you left a full bottle at room temperature, the half life of this process is about six months, meaning that a six-month old room temperature bottle of soda will be ~50% flat, even if you never ...


2

I would like to comment on your argument that says that when it is upright, despite the same volume, the surface is smaller, hence the pressure. This is where your reasonning is flawed. Indeed in your bottle, the pressure at the end is going to depend on the volume and temperature, not the surface area with the liquid. Surface area with the liquid would ...


53

The volume of the bottle and the volume of the liquid are the same both ways. By subtraction, the means the gas volume is the same either way. The difference assumes in the question’s reasoning doesn’t exist. There is more area in the sideways case. That’ll let equilibrium be reached more quickly. But it’ll reach the same equilibrium either way.


14

According to Henry's law the mass of gas dissolved is proportional to the pressure on top of the liquid. Because the pressure is the same in both cases, it should not matter if the bottle is vertically or horizontally


1

The amount of heat lost by the ice is proportional to the difference in temperature between the ice and its immediate surroundings. When sitting in still water, the water near the ice cools down so the heat transfer slows down. With running water the water is always warmer than the ice so the heat transfer does not slow down. See Newton's Law of Cooling.


2

Each of the three scenarios involve a different rate of heat transfer to the ice. Without getting into all the equations, the following is qualitative explanation. The slowest heat transfer rate occurs from still air to the ice. Air is a poor thermal conductor, so heat transfer from the air to the ice by conduction would be very slow. There is heat transfer ...


1

Heat moves between two media (in your example, the water and the ice) via three main mechanisms: radiation, conduction, and convection. Let's consider each in turn... Radiation is the transfer of heat via electromagnetic waves. It doesn't require the materials to be in contact -- a perfect example is how the sun feels warm, even though it doesn't touch us ...


2

The dry air is denser than the air with water vapor (water molecules in the gaseous state). Dry air is composed primarily of oxygen $O_2$ gas, molecular wt 32, and nitrogen gas, $N_2$, molecular wt 28. Water vapor is $H_{2}O$ gas, molecular wt 18. Therefore when lighter water vapor molecules replace heavier oxygen or nitrogen gas molecules, the density ...


2

Well, a balloon filled with wet air could float in dry air. This is because wet air is made of water vapor which has a lower density than dry air. However, in order for there to be a significant enough density different for the balloon to float the temperature would have to be extremely high. You can take a look at the image in this link to see. https://www....


0

It is static friction that prevents your foot from slipping. But static friction has a limit: $$f_s\leq \mu_sn$$ By taking a step, you exert a backwards force. Static friction then appears as the equal but opposite reaction force and pushes forward to avoid you slipping. As you walk faster, you exert more force. Since static friction must equal your force, ...


0

Because the tiedowns of the first two cases only restrict movement of the load in one direction, unlike the tiedowns of case 3. See this link: "Although mismatching of tiedowns could potentially result in real-world securement issues, the Agency believes § 393.106(d) concerning aggregate WLL deters such practices for what is commonly referred to as direct ...


2

When water freezes it expands. If you are freezing water in a sealed plastic bottle, this may stretch the plastic making it appear that the level has lowered when it returns to a liquid state in a slightly stretched bottle. However in a sealed container, where there is no loss from evaporation or sublimation, the amount (mass) of water does not change.


2

When water freezes its volume increases. This is one of the peculiarities of water. So when the ice changes back into water, its volume decreases back to what it was before it was frozen. In any case, the mass of the water does not change. Hope this helps.


0

look at this diagram $F=F(t)$ where: $F_i$ is your foot force $F_{\mu\,k}=\mu_k\,m\,g$ is the kinematic friction force between your foot and the surface. As long as your foot force is less then the kinematic friction force you don't move if you run then your foot force gradient is greater then as if you walk, thus: $\frac{dF_1}{dt} > \frac{dF_2}{...


5

While walking the static friction acts on your feet to hold it in a place and when you apply a force via pushing the ground backward it in turn pushes you forward (Newton's third law). Here you would see that your bones push your feet backward and hence are pushed forward and in a similar manner your whole upper body is pushed forward. This generates a ...


1

Water on a surface can lower the co-efficient of static friction, which will make it take less force to break static friction (shoe not slipping), and become kinetic friction (shoe slipping). Moving slowly on a wet surface usually causes less horizontal forces which can break the static friction between the shoe and the floor. Hydroplaning can also be a ...


0

Your experience is common; here is the explanation. Small amounts of electric charge can be moved about by friction between dissimilar, nonconducting materials (amber, glass, cotton cloth, floor carpets, shoe rubber, cat fur, etc.). If the charged surfaces are in humid air, they become sufficiently conductive to bleed those charges away before they get the ...


0

Rain clouds have larger droplets, which decreases the cloud's albedo (i.e. the fraction of light “reflected” by the cloud). From https://en.wikipedia.org/wiki/Cloud_albedo: The smaller the drops and the greater the liquid water content, the greater the cloud albedo, if all other factors are the same. And a few lines lower: In macrophysically ...


0

The coefficient of thermal expansion for aluminum is $24 \cdot 10^{-6} /K$. So raising the temperature by 50 degrees Fahrenheit ~ 28 degrees Celsius/Kelvin means it would expand by less than one thousandth. However, the difference needed is actually very small, on the order of a tenth of millimeters spread over several centimeters. So (1) should help (2) ...


0

Not really, but you don't need much. Yes, in case sticking is the main issue. Sugar syrup or honey softens when heated


2

The shape of a flame is set by where light is emitted from burning material. In many cases this is a gaseous reaction between air and vapor (evaporated stearin from the candle, pyrlolysed organic compounds from a log) that only happens in a certain concentration interval. So to calculate the shape you need to model the flow of air and flammable gas. This ...


-5

See Eur. J. Phys.37 (2016) 065806 (RG). They propose a model of cloth wringing. They suggest that initially the volume of wet rolled cloth contains fibers, water, and air, and calculate the volume change with wringing. The calculations with the model seem to agree with experimental results.


0

So my question is: Are the dogs doing any more work (or using any more energy) when trying to chase the cat than when they were gently tugging along? Intuitively I think yes, (especially given the gasping and panting coming out of both of them) Since work is strictly the product of force times displacement, or distance, in the direction of the force, ...


81

Rain clouds are dark because the part of the cloud you see is in the shade. Clouds are white because they contain tiny water droplets that scatter light of all colors equally in all directions. "Scatters light of all colors equally in all directions" means "white". But if you put a layer of white stuff over another layer of white stuff, the top layer will ...


2

If the dogs pull harder they do more work. Trivially: work is force times distance. The wording of your question leaves a small crack of doubt as to whether they are actually pulling harder after they see the cat: you include "(apparent)" in the title, and in the question say "the result was two dogs frantically trying to pull" [emphasis added]. Turns out,...


1

@Jame's answer is a more simplistic one to approach the problem. However, I agree with him that the dogs will be doing more work compared to if they don't pull the leash. But I want to discuss a case here of by "how much", it is not directly linear after all. Again, if we review, work is a dot product of two vectors. As a general rule, in your example, the ...


0

they are moving at the same speed and pulling the same weight (i.e. me) as before It's not that simple.You will notice that while keeping your dog steady you are leaning back. Degree of leaning back depends on the type of dog - more massive dog / it's power - bigger leaning will be. This game is a bit similar to Tug of War. Who wins ? The ones who have ...


0

I think the "explanation so far" does not exactly hit the point (Q1), and I try (Q2) another formulation: I understand that the setting is a room only lit by the light from the windows ("when the light from outside is neither completly dark nor very bright"). If you feel that it is hard to see well the light intensity will be so low that your eyes are no ...


1

Wall studs are vertical. This means to be spatially efficient, the two sides of a window must be vertical, straight, and parallel. The top and the bottom of the window, so long as what is above is not load bearing, can be whatever geometries will fit. If load bearing, the top and bottom must have structural integrity. The window must be framed properly, and ...


0

Yes. There is a maximum acceleration that your tires can provide.Be careful with sharp turns at high speeds where the centripetal acceleration is close to this limit. Any additional acceleration (or breaking) may cause the vechicle to slip out of the turn. If you decrease your speed, centripetal acceleration decreases and you will be more safely within ...


1

It has to do with this: In a perfect world, turns would all be banked so you could traverse each at full speed and not skid sideways off the road. Since it is not always possible to bank the roadway surface at the right angle to support a full-speed turn, the reduced speed limit in a turn is set to accommodate the existing bank angle and turn radius minus a ...


1

This is a perennial question on this site, and always leads to confusion over the distinction between "work" and "effort". To avoid confusion, we need to be explicit about the many terms in the energy. Energy contributions Crudely, the energy of the dog can be written as the sum of four terms, $$E = U_{\text{pot}} + K_{\text{KE}} + U_{\text{chem}} + K_{\...


2

The dog is doing more work becuse work = (force)(distance).So your dogs pull harder on you (more force) but don't move any faster so force is more while distance remains the same.


6

I think that there is somewhat of a biophysics question here but it is perhaps buried. In theory there is no contrast difference, but in practice... If you are designing for contrast in particular, there is almost no sense in which light-on-dark and dark-on-light can be properly distinguished in the abstract. Like, if "black" and "white" are consistently ...


0

Practical considerations are more often a factor than the visuals. Many Colleges are adept at chronically understocking their classrooms with pens. A small stub of chalk can still be used to make a good contrast line, but a nearly-empty pen will be barely visible. Similarly, if the professor is lazy and doesn't wipe the board properly, or doesn't use water ...


2

I am finding it easier to come up with questions than answers. Given you want textures of both writing instruments to be the same, you might consider a similar problem on your phone. It white text on a black background better than black text on a white background. Pixels make it easier to get a uniform comparison. Which is better? I believe some monochrome ...


2

When in free fall, neglecting air drag, the only force acting on your body is gravity, which is a non contact force, and you feel weightless. In other words the feeling of “weightlessness” is that of not experiencing the sensation of any contact forces. Stand on the ground and you feel the upward contact force of the ground on your feet that opposes and ...


3

It's because what you feel is distortions to your body's shape. When in free fall, when air resistance is low, every part of your body is accelerating very nearly the same amount. No difference in force between any parts of your body means your body doesn't have to exert any forces to keep its shape, so you don't feel anything. If the gravitational field ...


1

My previous answer with the example of the dog exerting the same force but doing less and less work I believe proved that physical effort does not always equal work as defined by Physics. That is how I interpreted, perhaps incorrectly, what your question was really about. But while it is also true, as @James points out, that if the dogs exert a greater ...


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