Tag Info

47

I can think of at least four things going on in this experiment that need pointing out: When you inflate a balloon by mouth, the air is warm: this makes the air inside the inflated balloon slightly lighter than the air it displaced The air inside the balloon has 100% relative humidity at 37C, and condensation will quickly form on the inside of the balloon ...

29

That's a perfectly good way to show that the density of air increases with pressure, and therefore that air must have a mass. When the scales tilt down on the side of the unburst balloon it shows the volume contained within the balloon has a higher mass than the same volume of air at atmospheric pressure. This means the density must be greater. we don't ...

25

Groups in Seattle, Colorado, and perhaps others managed to measure and verify Newton's inverse-square law at submillimeter distances comparable to 0.1 millimeters, see e.g. Sub-millimeter tests of the gravitational inverse-square law: A search for "large" extra dimensions Motivated by higher-dimensional theories that predict new effects, we ...

19

The lists will end up being huge, therefore I will only mention a few of each. This is my attempt of an answer: Successes of the Standard Model: Perhaps the biggest success of the Standard Model is the prediction of the Higgs Boson. The particle has been experimentally verified in 2012 (if my memory serves me well) after it has been theorised for over 50 ...

15

Measure the gravitational attraction between two atoms? Heavens no. That's such a tiny, tiny attraction. The atoms will be attracted to themselves gravitationally, but only minutely. They'll be attracted gravitationally much more strongly to the Earth, to the lab setup and measuring equipment, to the buildings around the measuring equipment, and even to the ...

10

John Rennie's answer correctly points out that the correct chain of reasoning here is a bit complex: On one side of the balance we have a column of air going up to space, a balloon, and some compressed air, and have displaced an amount of the air column equal to the volume of the compressed air. On the other side we have a similar column of air and a ...

5

Real physical theories are constructed on the ground of experiments. What I mean is that a model like the Standard Model of Particle Physics was not born as it is currently. There were lots of attempts, trial and error, etc. The success of the current SM of particle physics is mainly because one can explain lots of experimental evidence within its ...

5

There is a much better description here of Fizeau's nineteenth century experiment. Some of the key features that enabled Fizeau to succeed: A lens to collect the light from the source A collimating lens to prevent the light diverging during its journey A large diameter beam to minimise broadening of the beam by diffraction More lenses to focus the light ...

4

If you mean listening in the air while crushing the bag under water - the main reason is due to the different acoustic impedances of air and water. Transmission of the sound of the bag popping through the water probably plays a secondary role. Acoustic impedance is defined as $I =\rho c$ where $\rho$ is the density of the medium, and $c$ the sound speed ...

4

While the experiment you describe is legitimate, it has a complexity that could make it difficult to understand ("oh, my breath has mass!").   The simpler way to do this is to put a container (I've seen a basketball used, but balloons work as well) on a scale or a balance with regular weights on the other side. Use a bicycle pump to ...

4

An airplane's propulsion does not depend on friction between its wheels and the runway so the relative motion of the runway to the body of the airplane has no effect on the plane's motion$^1$. For example an airplane can take off from ice, where the friction between the wheels and the runway surface is effectively zero. So the plane would take off normally ...

3

(Skip to the bottom for a list of classical and quantum-mechanical effects of gravitation that have been observed in subatomic particles; my attempt to explain quantitatively what it would take to measure atom-atom gravity got longer than I'd intended, and I haven't had time to shorten it yet.) Let's suppose you want to measure the gravitational attraction ...

3

A lot of things are possible if you want to throw a lot of money at it. Is it practical? No. First, I would estimate that a rocket would be thousands of dollars. Low Earth orbit would get you the high range ($10^{-6}$ torr), high Earth orbit would possible get $10^{-9}$ torr. The next difficulty is to have the container returned to Earth (it needs to be ...

2

To make a long story short - Yes, it is possible, but you would have no practical reason to do it. To make a long story long, read on. While space is not a perfect vacuum, like you stated, it is close, and many applications of earth-generated vacuums are for simulating the conditions of outer space. In theory, one could put a pressure vessel in a orbital ...

2

It is well-known (but surprisingly hard to find a good reference for) that the probability of a photon being transmitted through some device is the fraction of the incident power of the classically transmitted through it. (See, for example, here). If you first create a linearly polarized wave/photon beam by sending it through a linear polarizer, and then ...

2

Tungsten has been known to bait gold bars (historically). There are a few methods we use to determine if something in front of use is gold or if it is alloyed, or if its plate, fill or scrap. You can cut the bar in half...You will then know immediately of you got bunk gold. You can do a specific gravity check of your gold. There are scales designed for ...

2

The algorithms used are as many as the experimental setups times the detectors used in the setups. They are built to fit the detectors and not the other way around. The common aspects are a few 1)charged particles interact with matter ionizing it and one builds detectors where the passage of an ionizing particle can be recorded. It can be a bubble ...

2

An jet/propeller airplane is traveling on a giant treadmill at takeoff speed. With respect to what does the plane have takeoff speed? I believe the following two statements are uncontroversial: (1) if the plane has takeoff airspeed (or greater), the plane can takeoff. (2) if the plane does not have takeoff airspeed (or greater), the plane cannot ...

2

While aliasing is a real concern for anything where sampling is involved1, it is really unlikely for this to cause a big zero-peak in frequency space, for an accelerometer on an animal (where it's unlikely that there's an oscillation precisely in sync with the sampling clock). Of course it's possible that a lot of the measured signal had nothing to do with ...

2

On a plot of $\Omega_\Lambda$ versus $\Omega_M$, there are three sets of observations that provide constraints: supernovae, the cosmic microwave background, and baryon acoustic oscillations. These three regions in the $\Omega_\Lambda$-$\Omega_M$ plane all have a common region of intersection, which is quite small. If they had failed to overlap, it would have ...

2

Sometimes it's helpful to explain the rationale of experimental design to a student as testing "competing alternative hypotheses." A positive result by this experiment would be strong evidence against the alternative hypothesis that the air blown into the balloon has no mass. A negative result however would not prove that the air has no mass. Further ...

1

To actually measure the 3D band structure is quite a difficult proposition. In materials that are quasi-2D (materials that are weakly bonded along one axis), the best probe of band structure today is angle-resolved photoemission spectroscopy. However, it only probes the band structure of the occupied states. For instance see the Fermi surface map of Sr2RhO4 ...

1

Another reason is that due to the inertia of the water the plastic can't accelerate as quickly and it needs to accelerate very quickly to make those noises. http://www.quora.com/Physics/Why-do-some-types-of-plastic-wrappers-make-so-much-noise-when-crumpled

1

In addition to the direct ground vibration and acoustic transmission paths into the detector, for most low frequency motions, you will be most sensitive to the near-field gravitational force (i.e. not the radiation, but just the usual "Newtonian" change in the potential). Assuming that you locate the detector far enough away that the radiation term is ...

1

Without knowing more about the specific situation, the first likely culprit is aliasing. This occurs when you are sampling at a frequency $\nu_s$ that is too low compared to the largest frequency that is sizeably present in your timeseries. More specifically, Nyquist's theorem guarantees you that if the highest frequency present is $\nu_M$, then a sampling ...

1

For Special Relativity (SR) i think the Michelson-Morley experiment is compatible and provides a verification of SR principle (some other formulations are also compatible with the experiment). Quantum Field Theory and especially the Dirac prediction and verification of positron is also a verification of SR (and many other expreriments in this context) For ...

1

The key output of the FLRW metric is the scale factor $a(t)$ as a function of time. From this we can calculate the time derivative $\dot{a}(t)$ (which is what the red shift measures) then check whether or not it satisfies the equation: $$\left(\frac{\dot{a}}{a}\right)^2 = \frac{8\pi G}{3} (\rho_{radiation} + \rho_{matter} + etc)$$ where the etc includes ...

1

One simple test that directly probes the model is the consistency relation between the angular diameter distance $d_A(z)$ and the luminosity distance $d_L(z)$ $$d_L(z) = (1+z)^2 d_A(z)$$ This relation holds regardless of the content and state of the Universe. If this is found to be violated then it would be a hard blow against the Friedmann Universe as one ...

1

The Friedman model is derived from General relativity under the assumptions that on cosmological scales the Universe is homogeneous and isotropic. Therefor you could falsify the Friedman model by Showing that on cosmological scales General Relativity is not a valid model (well it could happen) Showing that on cosmological scales the universe is not ...

1

You may be aware that both torque and angular momentum can be represented as a vector - and that such vectors follow the normal rules of vector addition. Thus, if you have equal rotation about both the X and the Y axis, what you really have is rotation about the XY axis; and in general, rotation about an arbitrary axis can be projected onto the X, Y and Z ...

Only top voted, non community-wiki answers of a minimum length are eligible