# Questions tagged [order-of-magnitude]

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### What exactly is order of magnitude?

I am little bit confused with what order of magnitude is. In my book it says, when we write approximate values of quantities in powers of ten i.e $10^b$, then $10^b$ is the order of magnitude. But ...
114 views

### What does it mean that gravitation separated from the four forces at $10^{-36}$ seconds?

Physicists have used math to calculate that gravitation separated from the 4 forces at 10^-36 seconds after the big bang, which is even before the inflationary period. The universe was still smaller ...
1 vote
38 views

### Steady Couette flow where the moving wall suddenly stops

Let it be a planar Couette flow for an incompressible fluid with dynamic viscosity $\mu$ and density $\rho$ that has reached the steady-state. Assuming that the plates are placed at the $xz$ plane, ...
1 vote
31 views

### Scaling difficulty of landing a rocket

I am wondering whether it is more difficult to land (as spaceX does) a rocket of height $k L$ than landing a rocket of height $L$? Is there some scaling law? Or at least is there a way to see in the ...
1 vote
135 views

### Why is $\exp(-1)$ a good benchmark in many physics? [closed]

In many subjects in Physics (not only phys though), we often encounter a value which gives $\exp(-1)$, such as a time constant in circuitry ($\exp(-t/RC)$, $t=RC$ gives $exp(-1)$), lifetime, mean free ...
3k views

### Are neurons more energy efficient than transistors?

In terms of order of magnitude, how does a the energy consumption of a typical mammalian neuron (in the brain) compare with the state of the art MOSFET?
1 vote
37 views

### Explain the theory behind this problem(if possible using number line or graph or any other method of pictorial representation) [closed]

In a situation in which data are known to three significant digits, we write 6.379 m = 6.38 m and 6.374 = 6.37 m. When a number ends in 5, we arbitrarily choose to write 6.375 m = 6.38 m. We could ...
29 views

### Could the ITER central solenoid lift an aircraft carrier 2 m into the air?

This claim is made in many places around the internet, presumably repeated from an ITER press release. But are there caveats? Does the aircraft carrier need to be in water (so only the no-longer-...
1 vote
373 views

### How many waves are in the ocean? [closed]

XKCD #2741 mentions in the title text It's cool how, when there's a number lots of people are curious about, but which isn't easy to measure, some random guess will get cited everywhere and become ...
150 views

### Is it just a coincidence that the range of order of magnitude of length and time is $10^{41}$ does it have some explanation?

The ratio of the longest and shortest lengths of objects in our universe is about $10^{41}$. Interestingly enough, the ratio of the longest and shortest time intervals associated with the events and ...
1k views

### Comparing the strength of gravity and electricity

I often see and hear people claiming that "the gravitational force is much weaker than the electromagnetic force". Usually, they justify it by comparing the universal gravity constant to ...
81 views

### How to incorporate HEP into the naive picture of QM?

When I explain QM to non-physicists, I sometimes say that quantum effects are typically noticeable on very small scales. For example, a QM particle in the harmonic potential behaves mostly classically,...
95 views

### What is the smallest time that the current technology can measure?

Many physical phenomena are associated with unbelievably small time scales. Let me give a few examples. The time scale associated with visible light is $\sim$ a femtosecond ($10^{-15}$ sec), The ...
74 views

### What is the value of electroweak scale? Depends on literature?

Depending on the literature, we see for the electroweak scale the following typical values : 100 GeV, 125 GeV (Higgs mass), 246 GeV (vev), 1 TeV So what is really the value of electroweak scale?
320 views

### Order of magnitude of zero?

I was wondering what exactly the order of magnitude is of 0. Just by calculating it you obviously get $-\infty$ because of the logarithm but is this really correct?
516 views

### What does the resistance of same order means in wheatstone bridge means?

As we know that in order to increase the sensitivity of wheat stone bridge resistance are of same order but here what exactly order means can anyone give me an example of this order?
279 views

### Understanding importance of Planck energy

Planck length is considered to be smallest length possible in the universe. Planck time is smallest time interval possible. Similarly what is importance of Planck energy because it is neither ...
527 views

### How do physicists compare the relative strengths of the four forces?

Since the four forces are different, with different force carriers, how are they (seemingly) directly compared? I often read that the weak force, for example, is many orders of magnitude stronger ...
188 views

### Nucleus vibration

What are the frequencies of the vibrations of the atom's nucleus? Is it in the quadrillions? Vibrating molecules is not the same thing - which is addressed as phonon vibration.
63 views

### Multiple levels of expansion of space? [closed]

It can easily be seen from the plot that there are at least 3 gaps between objects in the large, there is the gap between the planets and the moons, and between the planets and stars, and between ...
1 vote
59 views

### Why is quantum gravity so tough to be proved experimentally?

A great deal of particle physics experiments are going on in CERN and similar experimental labs and their study is based on quantum field theory? But I could not understand why quantum gravity is so ...
1 vote
135 views

### The answer to this question is not close to the age of the universe, then why do we say it is?

I saw this question in our textbook A great physicist of the century (P.A.M. Dirac) loved playing with numerical values of Fundamental constants of nature. This led him to an interesting ...
138 views

### Why does everyone seem to assume that gravitational waves will always be very small? [duplicate]

The size or effective distortion field of a gravitational-wave perturbation at any given location in space-time is determined by the distance separating the source and that location. This describes a ...
109 views

### Order of magnitude radiation measures conversion?

Standard unit of ionizing radiation dose is Sievert. I can get a rough idea of how dangerous absorbing various amounts is from https://xkcd.com/radiation/ and other sources. There are many other ...
65 views

### Why does the universe manifest scale?

I'll try outline my question in clear terms, articulating specific aspects that are its primary motivators. I'm just beginning in my exploration of physics as a student, but a persistent question that ...
627 views

### Why do people not have gravitational attraction? [closed]

Gravitational theory says every thing that has mass attract each other. So why don't people attract each other and overlap
111 views

### How do you calculate Reynolds and Mach's numbers before solving the Navier-Stokes equations?

Apologies in advance if the question is trivial. I am accustomed to electromagnetics but an amateur on fluid dynamics. My understanding is that the Navier-Stokes equations are solved to determined ...
65 views

### Sun's energy and grand unification

According to Wikipedia, The approximate grand unification energy value is equal to $1×10^{25}$ eV or $10^{16}$ GeV This is equal to $1602176$ J. Now, The Earth receives 174 petawatts (PW) ...
1 vote
98 views

### When is the order of magnitude not equal to the exponent of scientific notation?

Explain why the order of magnitude is sometimes not the same as the exponent in scientific notation. It is because of the units?
1 vote
185 views

### Where is the line between Quantum and Relativity?

Its often said QM is for the very small and GR for the very large. This brings to mind that there should be some limit at which one starts to apply and the other stops. Now I know there are more ...
147 views

### Different approch on Order of magnitude confusion [closed]

My problem: How many orders of magnitude larger is the sun $(1.99$ x $10^{30} kg)$ than the moon $(7.32$ x $10^{22} kg)$. Justification 1: So according to my teacher, we can do this question by ...
132 views