1
vote
4answers
9k views

What is the general formula for a trebuchet?

What I'm really looking for is a formula for a trebuchet that I can input the desired initial velocity after launch and mass of the object, and from that figure out how long the long arm, short arm, ...
2
votes
1answer
371 views

Lagrangian and Equilibrium Points

I'm wondering whether you can tell quickly just from looking at a Lagrangian whether a given point $q^0$ is an equilibrium point. Obviously all you have to do is verify it satisfies the E-L equations, ...
2
votes
3answers
934 views

What is the general approach to calculating time of impact in 3D?

Given two objects a and b moving at fixed velocities, how would you determine (a) whether they will collide at all, and if so, (b) time of impact? (Let us assume these are spherical bodies each with ...
6
votes
2answers
138 views

How does the Sun's magnetic field continue to exist at such high temperatures?

The temperature at the surface of the Sun is apparently well above 5000 C; I'm assuming the layers beneath the surface may be even hotter. At school, we learned that heating a metal beyond a certain ...
2
votes
2answers
122 views

Driving a solution of optical isomer molecules with the resonant frequency

What happens when we drive a solution of optical isomer molecules (enantiomers) with a microwave radiation in resonance with the tunneling frequency of the molecules (the frequency of the transition ...
3
votes
2answers
1k views

Would a rocket burn more fuel to get from Earth's surface to LEO, or to get from LEO to GEO?

Would a rocket burn more fuel to get from Earth's surface to Low Earth Orbit, or to get from LEO to Geosynchronous Earth Orbit?
3
votes
1answer
6k views

Understanding tension

I'm trying to understand tension. So here it goes: I'll start from the beginning. Let's assume I'm in space and can move around and apply forces. Let's say a rope is attached to a body(which is in ...
4
votes
1answer
208 views

Event Horizon fluctuating due to gravitational waves

Do the interiors of black-holes create gravitational waves and if so do these waves cause the radius of the event horizon to fluctuate as the waves pass the horizon ?
64
votes
7answers
5k views

Does juggling balls reduce the total weight of the juggler and balls?

A friend offered me a brain teaser to which the solution involves a $195$ pound man juggling two $3$-pound balls to traverse a bridge having a maximum capacity of only $200$ pounds. He explained that ...
0
votes
2answers
1k views

Electric scooter acceleration

I tested two electric scooters with almost same power (1500 W), but very different performances: A "Zem Star 45" (1500 W, 60 Nm) can reach 50 km/h in "a few seconds" (not measured actually), An ...
4
votes
1answer
172 views

What is the mass of the emergent magnetic monopoles in spin ice and how is the mass of an emergent particle determined?

In solid state physics emergent particles are very common. How one determines if they are gap-less excitations? Do the defects in spin ice called magnetic monopoles have mass? What is the mass of ...
4
votes
1answer
459 views

Tracking down the locality assumption in a CHSH inequality derivation

CHSH inequality requires both locality and realism. I will equate here realism with counterfactual definiteness. Now counterfactual definiteness tells us that given two different measurements on the ...
0
votes
2answers
154 views

Why is the critical density of the Universe non-zero?

I'm missing something and I wondered if someone could enlighten me. As I understand it, Einstein's equations say, among other things, that matter curves spacetime. I also understand, the Universe has ...
6
votes
5answers
910 views

What is the meaning of following expression $C=\frac{\delta Q}{dT}$ mathematically?

Our professor raised the following question during our lecture in Statistical Physics (even so it's related to Thermodynamics): Many text books (even Wikipedia) writes wrong expressions (from ...
0
votes
1answer
151 views

Liquid analog of the Black Hole (Part 2)

Similar question has been asked but did no get good answers. We know that black hole can confine light, but can we create an ocean black hole - which can confine surface water waves or sound waves in ...
0
votes
0answers
23 views

atomic friction [duplicate]

Possible Duplicate: Friction between atoms in spring thanks john:when we apply a stress within elastic range of metal/spring,due to flow of atoms the particular void(defect) region getting ...
1
vote
0answers
86 views

Effects of EMP in superconductor-based devices/equipment?

What are possible effects of electromagnetic pulse / EMP on superconductor-based devices/equimpent/transportation? Are they resilient or more sensitive to EMP?
0
votes
1answer
113 views

picture of newtonian gravity and black hole

We assume that the earth planet is a black hole. When a light beam is fired. The only way that even light can move is A and B which means this is impossible that light move on other ways C, D, E ...
0
votes
1answer
168 views

Acceleration of table tennis racket

I can't find any numbers about table tennis. What accelerations occur during a forehand smash for example? Thanks in advance & kind regards, Hans
1
vote
2answers
203 views

Is a compact universe consistent with the results of (for example) the Michelson-Morley experiment?

If the universe is compact then there is a twin paradox that is resolvable only by selecting a preferred inertial reference frame (arXiv). I was under the impression that the lack of a preferred ...
1
vote
1answer
252 views

Friction between atoms in spring

if i doing experiment on spring-mass system in vaccum,if i pull the to some extent (within elastic limit of spring) & let it go,will the system oscillate indefinitely? (neglect contact frictions ...
3
votes
1answer
195 views

Laplacian of a delta function as an interaction potential for Laughlin state

I am reading Xiao-Gang Wen's paper "Pattern-of-zeros approach to Fractional quantum Hall states and a classification of symmetric polynomial of infinite variables", on page 8, he gives three ...
1
vote
0answers
59 views

Temperature measurement, precision

I am having problems with one of the problems I have done (a) which is basically $\theta = 273.16K (19/15) = 346.00K$ For (b) I am given that the length is 15.00cm when the thermometer is incontact ...
6
votes
1answer
320 views

What is the angle at which water is splashed when a vehicle tyre rides in water on the road?

I would like to know the following: What is the angle at which water gets splashed when I ride my vehicle through a water on the road? How does angle of water varies with speed? What is the relation ...
2
votes
3answers
15k views

Sinusoidal Wave Displacement Function

I am learning about waves (intro course) and as I was studying Wave Functions, I got a little confused. The book claims that the wave function of a sinusoidal wave moving in the $+x$ direction is ...
3
votes
4answers
2k views

Was the Universe's entropy equal to zero at the Big Bang? Is zero-entropy state unique?

It is postulated by many cosmologists that at the Big Bang time the universe was in an unusual low entropy state. Does this claim specifically mean that the entropy of the initial universe was zero? ...
0
votes
1answer
217 views

detect movement - how does it relate to G force

I would like to detect if a user is moving by using an android smartphone - walking or jumping doesn't matter - want to know if the user wearing the smartphone is moving. I have found this code ...
2
votes
5answers
581 views

Could Quark model turn out to be false?

Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. Due to a phenomenon known as color confinement, quarks ...
6
votes
2answers
684 views

Intuition for gauge parallel transport (Wilson loops)

I'm looking for a geometrical interpretation of the statement that "Wilson loop is a gauge parallel transport". I have seen QFT notes describe U(x,y) as "transporting the gauge transformation", and ...
0
votes
1answer
412 views

Space Rocket Lift Efficiency and the Gyroscope?

I'm no physicist apart from basic 3d web animation, I'm just curious and please feel free to correct my misuse of terms or inadequate speculations. I've been reading a lot on gyroscopes and ...
22
votes
8answers
5k views

Why are L4 and L5 lagrangian points stable?

This diagram from wikipedia shows the gravitational potential energy of the sun-earth two body system, and demonstrates clearly the semi-stability of the L1, L2, and L3 lagrangian points. The blue ...
1
vote
1answer
140 views

Ratio of the isospin of the photon

as known the photon can have an isospin of 0 and 1. However, what is the ratio of both for an virtual photon (in e+e- annihilations)? Next to an 1^-- resonance like J/Psi or Psi' it should be 1 in ...
1
vote
1answer
108 views

Excitations implied by symmetries

I read that in condensed matter field theory a symmetry implies not only a conserved current (through the well-known Noether theorem) but some kind of "low energy excitation". I am familiar with the ...
4
votes
2answers
4k views

Unit of torque with radians?

Usually, the angular frequency $\omega$ is given in $\mathrm{1/s}$. I find it more consistent to give it in $\mathrm{rad/s}$. For the angular momentum $L$ is then given in $\mathrm{rad \cdot kg \cdot ...
4
votes
0answers
209 views

Quantization and natural boundary conditions

The Euler-Lagrange equations follow from minimizing the action. Usually this is done with fixed (e.g. vanishing) boundary conditions such that we do not have to worry about any boundary terms. ...
3
votes
3answers
367 views

In the classic viscosity definition, why does doubling the plate gap cause the force to halve (intuitive)?

I am puzzled by an artifact of the definition of viscosity and need an intuitive picture to help explain it. I know $\tau_{yx}=-\mu{dv_x \over dy}$ but I am looking for an intuitive picture of the ...
4
votes
2answers
2k views

How to make the projected image smaller by adding one ore more lenses in front of the built in projector lense?

I have a projector that creates a large image, even if the distance to the screen is short. The device is very small, approximateley 10x10 cm if you look from above. The height is only 3 cm. I ...
0
votes
2answers
617 views

Closest model for relationship between velocity and distance

Which is the model that best shows the relationship between velocity and distance: $v \propto d$ $v \propto d^2$ $v^2 \propto d$ $v^2 \propto d^2$ What I think is from: $$v=at \Rightarrow ...
11
votes
2answers
1k views

Is ultradense deuterium real?

I've found several articles discussing experimental evidence of a deuterium state of densities over $140 \textrm{ kg}/\textrm{cm}^3$: F. Winterberg. Ultradense Deuterium. arXiv. Shahriar Badiei, ...
0
votes
2answers
141 views

Showing that electron and positrons have the same absolute charge

In Zee's quantum field theory in a nutshell, 2nd edition, pg 551 he has the charge of a Dirac field written as $Q=\int {d^3p \over (2\pi)^3(E_p/m)} \sum_s ...
0
votes
0answers
25 views

Can you recommend me a book on the discoveries and properties of these particles? [duplicate]

Possible Duplicate: Good book about elementary particles for high school students? Some days ago, I've found this: When I was in high-school, They taught me about electrons, protons and ...
10
votes
3answers
3k views

why aren't there nuclear powered aircraft?

I know this might sound like more of an engineering question that about physics, and it probably is, but bear with me: i'm still not sure if the answer to my question lies in the physics or in the ...
7
votes
1answer
800 views

Relativistic drift velocity of electrons in a superconductor?

Is there a formula for the effective speed of electron currents inside superconductors? The formula for normal conductors is: $$ V = \frac{I}{nAq}$$ I wonder if there are any changes to this ...
1
vote
2answers
165 views

Why does letting air into a box of wine help the flow?

I've notied that when I get down to the last part of a box of wine, the flow slows to a trickle. If I open the nozzle, tilt the box back (letting air gurgle into the bladder) and then tilt it back ...
15
votes
2answers
2k views

Self energy, 1PI, and tadpoles

I'm having a hard time reconciling the following discrepancy: Recall that in passing to the effective action via a Legendre transformation, we interpret the effective action $\Gamma[\phi_c]$ to be ...
4
votes
3answers
299 views

How far from the Sun is a photovoltaic effective?

Just what the title states. Photovoltaic cells convert incident light to electricity; this probably means they create less electricity when it is dark - as in deep space. How far can a solar cell ...
1
vote
0answers
57 views

Would ferromagnetic space debris have been magnetized by their orbit in the Earth's magnetosphere?

Given a nail, and a magnet it is possible to magnetize the nail by patiently rubbing the nail until it is magnetized; albeit the field strength may be less than that of the source. With several ...
0
votes
1answer
837 views

Vector Displacement [closed]

A novice golfer on the green takes three strokes to sink the ball. The successive displacements are 4.10 m to the north, 1.90 m northeast, and 1.00 m at 25.0° west of south. Starting at the same ...
3
votes
3answers
1k views

Maxwell equations invariant under Lorentz transformation but not Galilean transformations

Why Maxwell equations are not invariant under Galilean transformations, but invariant under Lorentz transformations? What is the deep physical meaning behind it?
4
votes
1answer
206 views

Is the fuel burn for a satellite launch affected by the position of the moon relative to the launch site?

The gross mass of a satellite rocket is tiny compared to that of Earth, and Luna. Between them, however, the two bodies set up tides in bodies of water which itself is again considerable mass. At ...

15 30 50 per page