Constant Definition and 1000 Threads

Layman here, please excuse my ignorance. I believe to understand the basics of SR, GR, cosmic expansion, etc but questions come to mind now and then. As I understand, dark energy, the cosmological constant, vacuum energy, whatever you may call it, remains a constant per space volume unit. Empty...

A disclaimer: I'm trying to limit myself to asking questions on Physics Forums, partly because I feel I've gone way past my quota. Still, there is one question that simply won't go away, and it concerns the relative efficiencies between two forms of motion. The first involves continuous...

The Einstein gravitational constant (Κ) is usually written as; Κ = 8πG/c4 Can this constant be represented as wave-particle ratios of force? One ratio is a thermal ratio, it includes Plank temperature and Hawking temperature. The other ratio is a particle ratio including Plank mass. Can...

Homework Statement The 500-mg balance wheel of a certain clock is made up of a thin metal ring of radius 16 mm connected by spokes of negligible mass to a fine suspension fiber as in(Figure 1) . The back-and-forth twisting of the fiber causes the wheel to move in simple harmonic motion with...

Homework Statement We have a mass m at x = 0 attached to a spring with spring constant k which is moving at constant velocity v such that the position of the spring is described by X = l + vt where l is the equilibrium length of the spring. Solve for the motion of the mass. Homework...

H=p^2/2m+c What's c? It's of course a shift in energy, but can be thought also as a smoother and smoother real-space local potential that becomes a constant all over the space. On the other hand, why couldn't one think about it as a constant potential in reciprocal space? It's a shift in energy...

Homework Statement The shielding efficiency of an aperture depends on e−αd, where α is the frequency-dependent attenuation constant of the aperture and d is the thickness of the material (or the cutoff waveguide) at frequencies below cutoff. where ωc=2πfc. Calculate α for an air-vent...

Homework Statement A yo-yo has a moment of inertia of 75.0 g-cm2 about its rotation axis. What is the constant torque required to make it spin to 300 rev/min in one second, starting from rest? Homework Equations ∑ = Iα The Attempt at a Solution I was thinking since the question is asking for...

Homework Statement A box is dragged a distance d across the floor by a force F which makes an angle theta with the horizontal. If the magnitude of the force is held constant but the angle theta is increased, does the work remain the same, increase, decrease, or first increase and then decrease...

Homework Statement [/B] Consider a barbell with two equal masses m that rotates around a vertical axis z not passing through its center with angular velocity \vec{\omega}. The barbell is forced to stay in this position by an appropriate support. Identify the forces exerting torques on the...

A slab made of unknown material is connected to a power supply as shown in the figure. There is a uniform magnetic field of 0.7 tesla pointing upward throughout this region (perpendicular to the horizontal slab). Two voltmeters are connected to the slab and read steady voltages as shown...

I 'd like to clarify some doubts about the rotational motion around a fixed axis of a rigid body, in the case the angular momentum vector \vec {L} is not parallel to the angular velocity \vec {\omega} . In particular, consider a horizontal barbell with two equal masses m , forced to rotate...

This Invited Review article just came out: http://arxiv.org/abs/1603.08658 The Atoms Of Space, Gravity and the Cosmological Constant T. Padmanabhan (Submitted on 29 Mar 2016) I describe an approach which connects classical gravity with the quantum microstructure of spacetime. The field equations...

Why does the free space permittivity has the value it has?

Homework Statement Ok so here is the prompt: a 3kg object is fastened to a light spring over a pulley. The pulley is frictionless and its inertia may be neglected. The object is released from rest when the spring is unstretched. If the object drops 0.1 meters before stopping, find the spring...

Homework Statement I am trying to use a slide wire potentiometer and a galvanometer to find the electromotive force of an unknown cell. I have heard that the balance point at which the galvanometer needle has zero deflection should be towards the centre of the slide wire as this reduces...

Homework Statement Prove that the diffusion constant D of an ideal gas can be expressed as D=1/3λv(v bar) where λ is the mean free pass of the gas molecule. And v bar is the average speed of the gas molecules obtained from the kinetic theory of gases.(Use the picture to setup the net flux...

Homework Statement (Working with geometrised units) Consider the EFE ##G^{\alpha \beta }+\Lambda g^{\alpha \beta} = 8 \pi T^{\alpha \beta} ## work out (using weak-field considerations) an upper bound for the cosmological constant knowing that the radius of Pluto's orbit is 5.9 x 10^12 m...

Homework Statement You are asked to design spring bumpers for the walls of a parking garage. A freely rolling 1100 kg car moving at 0.66 m/s is to compress the spring no more than 9.0×10−2m before stopping. What should be the force constant of the spring? Assume that the spring has negligible...

In an electromagnetic wave like light,both wavelength and frequency changes but it's speed always remains constant.Why?

It states "a pure chemical compound is always made up of the same elements combined together in the same fixed ratio by mass." But how can a compound have the same elements ? For example,let's take ethanol,it is composed of hydrogen,carbon and oxygen.So three elements and not the same element.

I have an object that is decently thermally insulated. I want to plot how a constant cooling power of a few watts for a few minutes is going to affect the object's temperature. I need to account for how much heat is leaking in. Getting a constant cooling doesn't seem easy. If I instead use...

Homework Statement Given the following wave function valid over -a \le x \le a and which is 0 elsewhere, \psi(x) = 1/\sqrt{2a} Find the uncertainty in \left<\left(\Delta p\right)^2\right> momentum, and the uncertainty product \left<\left(\Delta x\right)^2\right>\left<\left(\Delta...

Consider a stable circular orbit (with a central force) subjected to small perturbations. The orbit equation is given by (3.45). The text argues that the ##\beta## in (3.46) must be a constant over the domain of ##r_0##: "Otherwise, since ##\beta## can take on only discrete rational values (for...

The triplet spin state with a normalisation constant of 1/√2 and the singlet spin state with the same normalisation constant... Where on Earth is this normalisation constant derived from? I've been scouring the Griffiths intro to quantum mechanics textbook and can't find info on it.

Many have claimed that if dark energy was not so small then the universe would fly apart and we wouldn't be here. However what if you increased the value of lambda and at the same increased the value of the gravitational constant ( or perhaps the amount of matter or dark matter in the universe)...

Homework Statement my spring constant is 85 N/cm and I have to convert to N/m Homework Equations why does stoichiometry not work on this? How would I approach conversions like this? The Attempt at a Solution I tried converting the 85 N/cm to N/m and ended up getting 85*10^2 N/m. This was...

Hi, Could I please get some guidance on my approach and solution, for this particular problem. Any assistance welcome. 1. Homework Statement An ideal gas is compressed at a constant pressure of 1.3 atm from a volume of 20 L to 12 L. During this process it gives off 3.69 kJ of heat. What is...

In my springs what would the spring constant need to be If I am 1.8m tall and I weigh 68 kg

When we measure the cosmological constant Λ what we are really doing is measuring the longterm value of the Hubble rate, namely H∞, the distance expansion rate that the present rate H(t) is seen to be declining towards and leveling out at. It's convenient to write distance expansion rates as...

When does the value of the "Equilibrium Constant (K)" equal one ? and what does that mean ?

In my textbook it says an isothermal process occurs when the temperature is constant. It also said taht typically, Q,W, and delta U are not 0 in these processes. My question is how can heat not be 0 if temperature is constant? Q=mcDeltaT so if Delta T is 0, then Q also has to be 0 right?

Homework Statement I need to explain for a lab, why the efficiency of a rubber band slingshot constant for different stretch lengths. I don't need math, just a general explanation of why kinetic energy of projectile/elastic potential energy in rubber band is constant. Homework EquationsThe...

Homework Statement A block of mass 1 kg is attached to a spring. The spring extends by 10 cm. Find spring constant.Homework EquationsThe Attempt at a Solution Potential energy of spring = kx2/2 work done by block = PE Hence mg*x=kx2/2 ∴1*9.8*0.1=k*0.1*0.1/2 ∴k=196N/m But solution says mg = kx...

Piran et al., "Cosmic explosions, life in the Universe and the Cosmological Constant," http://arxiv.org/abs/1508.01034 I thought this was interesting. If I'm understanding correctly, the idea is that satellite galaxies such as the Magellanic Clouds have low metallicity, which causes them to...

Homework Statement Choose two masses and vary their separation, measuring the force between them each time. Plot a straight line graph and use the gradient to estimate the universal gravitational constant. Include uncertainties in the results and express values with the appropriate number of...

Homework Statement Not sure if this belongs in the 'Advanced' section so apologies if it does not. I am using a monochromator to measure spectrum lines from a rubidium lamp. From the data (wavelength of spectral lines plus transition number 'n') I am asked to use a graphical method to...

Homework Statement A parallel plate capacitor has a capacitance of 1.5µF with air between the plates. The capacitor is connected a 12V battery and charged. The battery is then removed. When a dielectric is placed between the plates, a potential difference of 5.0V is measured across the plates...

Homework Statement A parallel plate capacitor has a capacitance of 1.5µF with air between the plates. The capacitor is connected a 12V battery and charged. The battery is then removed. When a dielectric is placed between the plates, a potential difference of 5.0V is measured across the plates...

Homework Statement A sample consisting of one mole of a diatomic perfect gas is heated from 25 °C to 200 °C at constant volume. Calculate q, w, ΔU and ΔH for the process, given that Cv = 23.02 J K-1 mol-1 . Homework Equations Im studying for mid terms and i have no lecture notes on diatomic...

Big masses like planets and stars have gravitational fields. Gravitational fields curve space around them. So in theory a particle having mass moving at fixed speed, from its own perspective, will accelerate when moving closer to such a planet. It'll be moving at fixed speed in a curved space...

Generally in chemistry and physics, we learned that a material has a heat capacity at constant pressure. However, I am confused at whether this refers to a constant external pressure or a constant system internal pressure? Thanks.

For time independent Schrodinger's equation in 3-D Where Enx,ny,nz=(nx/Lx2+ny/Ly2+nz/Lz2)(π2ħ2/2m and Ψnx,ny,nz=Asin(nxπx/Lx)sin(nyπy/Ly)sin(nzπz/Lz) How do I normalize A to get (2/L)^3/2? I don't think I understand how to normalize constants.

Homework Statement A ball of mass m rolls down a 3.0 m ramp inclined at 30° above the horizontal, rolls along a flat, friction less surface, and collides elastically with another ball of mass 2m, initially at rest. The second mass then moves along the surface and collides with a horizontally...

Excuse me, If I want to calculate one equation in SI units. Which value of Boltzmann constant I should deal with. Also, the electron temperature it can be used in Kev or it should be in ev. Also, the nm must be converted to meter or it can be used in nanometer.

Could anyone please recommend a paper that accurately gives the value of the cosmological constant? Or else may you reply with values of the cosmological constant that you would you use in your research? Any help would be very much appreciated.

Ok, so here's the deal. I'm working on something that I SHOULD know the equations for after 5 years of school and a degree in mechanical engineering, but then again I can't remember why I walked into a room most times. So if ya'll could give me some guidance and at least a starting point I...

Is the amount of dark energy in the universe constant or else does it increase as the universe expands? In other words is the "anti- gravitational force" that is believed to be caused by dark energy and results in a accelerating universal expansion, a constant value or will it increase as the...

I am reading an article on Arxiv about modelling the electron structure in a nanowire crystal: http://arxiv.org/abs/1511.08044 But I am having trouble understanding the hamiltonians (1) and (2). In (1) what is the purpose of the term E_gap/2. Is that just a reference point for the energy or...

Homework Statement A Ti Rod is to be put into a furnace to try and increase the carbon content of the rod. Initially, the carbon content of the rod is 0.2%wt. The carbon content of the furnace is 1.0%wt. What would the temperature have to be in order to get a final carbon content in the Ti rod...