New answers tagged

1

When walking down an incline there is greater acceleration due to gravity. In order to maintain a walking speed, a braking force is needed to counteract the acceleration, and this braking force is given by the contact force of the initial footfall of each step as it's in front of your center of mass creating a force vector pointing away from your direction ...


0

It is difficult to ignore the physical effects because in modern systems there is disk brake system aand on pressing the brakes suddenly the car would start sliding and therefore tyre will wear down instead of breaks and in case of slowly braking the breakpads have to rub them to provide friction for the car to stop. but if you ignore this effect completely ...


4

From the perspective of both forces and power, sudden braking causes more wear even if the energy/work is the same because everything occurs over a shorter period of time. Higher instantaneous forces results in more stress and and higher power result in higher temperatures, therefore sudden braking causes more wear.


3

If the cloud density is constant, it seems denser near the horizon, because there are more clouds for the same angle of vision. The fact that the sun is near the horizon turns clouds brighter in that region, what calls our attention.


2

Or perhaps the wire shelf creates reverse electric feedback that can damage the magnetron over time? Yes. In a microwave oven, the microwave is not just a coil of wire with current going through it. Anything that absorbs the microwaves it emits (be it a spoon, a wire rack, a glass of water, or the water inside a piece of chicken) will absorb it by ...


0

Assuming the point of suspension as reference level and angle made by string with vertical as $\theta$. potential energy is defined as energy of system due to gravitational force of earth . *Potential energy= displacement from reference level* it should be $-mgl\cos(\theta)$ ...........where mg us the force and displacement from reference is $l\cos(\...


1

This is out of my reasoning so I can't be sure. When you slide the blade over the surface of the ribbon, the friction forces whatever is quasi monodimentional in the latter to be stretched in the sliding direction. This can applies to long single molecules as well to fibrils and fibers they may form. The stretching involves only one side of the ribbon, which ...


0

Most large metal structures such as power lines towers are grounded, which should make them rather poor in functioning as receiving antenna. But there may be other effects that sometimes improve reception nearby such objects. One mechanism by which large conductor can improve radio signal is the radio signal drives oscillations of electrons in the large ...


0

Very simple: The frequency for the up and down movement is twice that of the left and right swing. Plus the up and down excitation (acceleration) is not symmetric, a good part of it consists of overtones of even higher frequency. Actually the hair and attached head are in free fall between steps. So to get to the same amplitude, the hair would need to move ...


1

Your equation should be $$h=s^2A^2t^2/2gm^2$$ Your observations about ideal and human bodies do not contradict your theory. By definition ideal bodies are not real, so there are no observations of their behaviour. It is not contradictory for ideal bodies which do not deform (hence $t=0$) to break when $h=0$. For real bodies if $t$ is almost zero then the ...


3

The average impact force is $$F_{average}=ma_{average}=m\frac{\Delta v}{\Delta t}$$ Clearly, if $\Delta t=0$ the average impact force would be infinite. If the object is a human body jumping on his legs from a finite height, his bones don't break even if the collision is almost visibly non-elastic and $t$ is apparently too small. What is the reason behind ...


2

From a theoretical point of view this would be an open circuit, so there is not current flow and hence the accumulator won't discharge. On the other hand, nothing in the universe, is a perfect insulator. There is always the possibility that some electrons in the air can travel from one pole to the other and this condition is somehow amplified if there is ...


5

Not a complete answer, but a few notes. There is a significant amount of rotational force going on in the head and neck during running, so much that humans (as well as other running animals) have specific adaptations to help manage them. Cf "that pig can't hold its head still"[1]. I can at least find one source[2] finding that the head has a yaw (...


2

As @nuclear-hoagie said, the ponytail is basically a pendulum, so vibrations up and down are not really possible (or are much more complicated) as the hair would have to elongate itself in order to store the kinetic energy from the hair falling down so it cannot release it later. However the sideways and back and forth vibrations can be maintained almost for ...


51

The human gait has a natural bobbing motion, with the head moving slightly up-and-down and side-to-side. The side-to-side motion (swinging on an axis parallel to the nose) turns the ponytail into a natural pendulum which swings back and forth, since this plane of motion is gravitationally symmetric and has nothing to stop the swing. Small driving forces can ...


11

I think the longitudinal oscillations of a ponytail are quickly damped (more precisely overdamped), since they involve layers of hair sliding along each other, as well as inelastic collisions of the back of the neck. On the other hand, the transversal oscillations require merely twisting the ponytail near the elastic band holding it together. I think it ...


0

For water-based stains and paints, the color "in the can" does not match the color "on the board" after the stain dries. This is because the product is a water-and-resin emulsion that has a milky appearance when in the can, that disappears as the water evaporates and the resins cure. As that emulsion disappears, the true color of the ...


0

At the first order, they will reach at the same approximate time. The heat transfer due to convection is based on the difference between the surface temperature and the free air temperature, and is independent of their absolute values. However, when one gets into the nitty gritty, an "it depends" starts to surface. We can't treat the cylinder as ...


0

When the person starts to move, all its weight must be supported by feet and hand: The hands must do a force so that the torque be at least zero, otherwise the person falls down. Let's $\theta$ be the initial angle between the person and the ground, W his weight (supposed acting half its height $h$). The force $F$ from the arms is directed perpendicular to ...


1

Second one is definitely easy.Imagine your body like an inclined plane and theta is the angle made by your feet is theta with the floor. In second case your hand push up the cos component of your weight , while in first case your hand push up against $\approx$ mg. You can verify this , when you stand straight , theta made by feet is $90^o$. and when you ...


5

If we were dealing with a video camera, then this would likely be due to the stroboscopic effect. It is also called "the wagon wheel effect", and it's related to the Nyquist-Shannon sampling theorem. The stroboscopic effect is a visual phenomenon caused by aliasing that occurs when continuous motion is represented by a series of short or ...


4

this is called the "stroboscopic effect" but it does not occur in your eye, it occurs because the light (LED or fluorescent) shining on the fan blades or fidget spinner actually blinks on and off at the mains AC frequency. Under sunlight or incandescent light, the stroboscopic effect will not occur, and the rotating element will appear to your eye ...


5

There is, in fact, physics in this. It's a easier to understand in terms of a camera (the same phenomena happens to video) because we can talk about a frame rate. The human eye has sort of an effective frame rate, but this is far less fixed and hence makes the analysis a little more complicated. For a video camera, a picture is taken every so many seconds. ...


5

In addition to Ankit's brilliant answer I would also like to add that the sound can be originated from non - microscopic irregularities and the breaking of relatively large chunks. It causes a larger sound and for the same reason as said by Ankit .


15

So for this to understand, you must know what causes friction and what happens when two bodies rub over each other. When two bodies are in contact, the actual area of contact is lesser than their visible areas because the surfaces are not smooth and have irregularities(microscopic as well as macroscopic) on them (irregularities due to irregular arrangement ...


4

Imagine a bunch of vertical springs, and a board sitting horizontal on them. You pull the board, and friction between the board and the springs pulls the springs along with it. The springs have to stretch to accommodate this, and eventually the restoring force is greater than the friction force, and the spring moves back. Once it moves back, the restoring ...


1

If so, I don't think it's a significant effect. Otherwise, sugar would not flow as freely as it does. However, sugar is somewhat hygroscopic, and sugar that has absorbed water vapour from the atmosphere can stick together in lumps. In warm humid climates, that happens fairly quickly to sugar that's kept in an unsealed bowl. In cool dry climates, it takes ...


1

The tiny particles (of micron size) that the mask filters out is still much bigger than the dimensions of the gas molecules (of nano meter size) that we breathe. So the mask's ability to filter particles such as microbes is not necessarily a barrier to breathing. Pressure difference is created in the process of drawing a breath due to expansion of lungs. ...


1

According to this Wikipedia article https://en.wikipedia.org/wiki/Atmospheric_electricity There is a weak conduction current of atmospheric ions moving in the atmospheric electric field, about 2 picoAmperes (2 x 10$^{-12}$A) per square metre, and the air is weakly conductive due to the presence of these atmospheric ions. To put things into perspective, ...


6

This problem is best thought of in terms of magnetic circuits, which are mathematically analogous to electrical circuits with current replaced by magnetic flux, voltage (or electromotive force) replaced by magnetomotive force (MMF) and electrical resistance replaced by magnetic reluctance. The steel that the paper clips are made of is a magnetic material, ...


1

It is due to the ferromagnetic nature of iron paper clips in which magnetic domains in the paper clips get oriented along the magnetic field thus magnetising it . So amount of links depends entirely on strength of magnetic field . Regarding your last query, I think it is related to the cancellation of magnetic fields thus weakening the strength.


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