Constant Definition and 1000 Threads

I would like to clear out my understanding of gas compressor. If it is moving at constant RPM, is it mean that it can only allow same volumetric flow rate all the time? So the power will remain constant too, (P=VI) then voltage and current will varies. My investigation is to find why there is...

I am trying to model the maximum performance of a linear actuator assembly and create a flexible excel tool for calculating other systems in the future. The actuators are simple ball screws driven through a gearbox by a motor, typically BLDC so the torque is relatively constant over most of the...

If c_v is the specific heat at constant volume, authors substitute this into the first law as follows: c_v d\theta + pdv = dq How can one deduce that equation for any case? Since the specific heat at constant volume is used, the equation would be valid only where there is no expansion i.e...

Why is the dielectric constant smaller in few-layer materials than in bulk materials?

A simple harmonic oscillator consists of a block of mass 45 g attached to a spring of spring constant 240 N/m, oscillating on a frictionless surface. If the block is displaced 3.5 cm from its equilibrium position and released so that its initial velocity is zero, what is the phase constant, φ ...

Dear forum I am working with thermal radiation. This is the specific formula: P = σ ⋅ A ⋅ T4 P = emitted effect (W, J/s) σ = Stefan-Boltzmann constant (5,67 ⋅ 10-8) A = area of object (m2) T = temperature of object (K) How can I get to know the...

What is the effect in quantum if Planck constant is zero? Here are some points that I could think of: if Planck constant is zero, the Heisenberg Uncertainty Principles will become zero, therefore either momentum or position of a particle can be known exactly. if Planck constant is zero, both...

Suppose that there's a wheel. A constant torque is applied to the wheel from the central axis. What is the relationship between the amount of force received by each particle on the wheel in relation to the distance each particle is away from the axis?

I read a article now and It claims he found the cause of cosmological constant.Is that true ? The idea is actually good...

In a discharging battery, do current and voltage decrease over time? if so how does the battery accomplish the same amount of work over the course of its discharge with a lesser voltage or current?

If the speed of light is constant regardless of the state of motion of the source, then doesn't this imply that it is possible to calculate the velocity of a reference frame by measuring the time it takes for light to traverse some known distance in that frame. For instance if our frame is...

Hi there! I'm having some trouble understanding Hubble's Law and Constant and would be grateful for some help. So Hubble's Law shows that the most distant galaxies have the greatest red-shift, as they are moving away from us fastest. This shows that all galaxies are moving away from each other...

In the constant volume gas thermometer, T (°c)=[P(T)-P(f)]×100/[P(b)-P(f)] (P(T) means gas pressure at T°c P(b) and P(f) for the water's boiling point and freezing point) Is it right?

Homework Statement Why is the horizontal velocity for a projectile constant? I understand it physically, since the vertical and horizontal velocities aren't related and don't affect each other, g will only affect V_y and neglect V_x, so it's constant. But maths-wise, isn't V_x =...

[Note from mentor: this thread was originally posted in a non-homework forum, therefore it does not use the homework template.] ------------------------------- So I've been asked to prove that in a harmonic function where a(t)+w2r(t)=0 that (1) v(t).v(t)+w2r(t).r(t)=constant scalar and...

Homework Statement A person is standing over a well and drops a rock. After 2.4 seconds he hears a rock splashing into the water. Take the speed of sound to be 300m/s and calculate the depth of the well. Homework Equations x=v/t for constant velocity x=1/2at^2 for accelerated motion The...

Homework Statement Jupiter's moon Io has active volcanoes (in fact, it is the most volcanically active body in the solar system) that eject material as high as 300 km (or even higher) above the surface. Io has a mass of 8.94 × 1022 kg and a radius of 1815 km . Ignore any variation in gravity...

is mass of light constant

Hello, If I take a DC motor and put it in generator mode, what will happen if I connect a resistance at the wire ending of the DC motor? Will the motor turn slower compared to when the electric wire of the motor is connected to nothing? What effect will the resistance have on the current...

I know that the power of an engine is equal to (rpm*torque)/ 9.54 (SI units). But does this mean that an engine when turned on is outputting the same amount of energy per unit time, every time ? . What happens when we press the gas pedal, does the power output increases? When i drive my car...

Homework Statement How would i go about finding the electric field and potential difference when there is a constant charge density between the capacitor rather than a vacuum? Homework Equations int E dot dA = Qencl/epsilon0 V ab = int E dot dl The Attempt at a Solution to be honest I am not...

Has there been any recent changes in the G constant value?

Hi all, I'm new here on Physics Forums and can't wait to delve into some juicy topics! I have a very practical problem that I need help with. I am doing a home project where I want to move a platform on wheels (loaded to a maximum of 70kg) in a 1.5m long straight line across the floor at a...

< Mentor Note -- thread moved to HH from the technical physics forums, so no HH Template is shown >[/color] Could anyone please correct me if I have any mistake in the following question? It's very important for me to know if I am doing it correctly. 1) "Michelle, a technician at a spring...

Homework Statement At the beginning of a 10 sec. interval your position is measured to be 80 ft East with respect to a reference object. At the end of the 10 sec. interval your position is measured to be 965 ft East with respect to the same reference object. Determine your velocity at t = 3.45...

Hello,Lets say I start off with constant acceleration of 1 m/s^2, and I want to evaluate it at 3 seconds. a = 1. a(3) = 1 then, since at=v, v(t) = at = 1(3) = 3m/s then I can work backward v/t = a = 3/3 = 1 then, since vt = d d(t) = vt = 3(3) = 9 then I can work backward d/t= v =...

Homework Statement A rock is released from rest from the top of a very high cliff, and accelerates downward at g. Approximately how far does the rock travel in the first 7 seconds of its free-fall? (Assume no air friction.) Homework Equations X=Xo+VoT+1/2AT^2 The Attempt at a Solution I...

I just wonder if there were any serious (and peer reviewed published, to be in line with guidelines) theory, which had proposed some link between speed of light in vacuum constant and between gravitational constant G. For example a calculation of speed of light based on G. Tried google search...

Generally pressure in a liquid changes with height at which we measure. But still blood pressure remains almost same throughout the body. How is this possible?

Using the standard equation of a circle x^2 + y^2 = r^2, I took the first and second derivatives and obtained -x/y and -r^2/y^3 , respectively. I understand that the slope is going to be different at each point along the circle, but what does not make sense to me is that the rate of change of...

Gas pressure in a closed chamber at constant temperature will last forever, unless leaking or chemical reactions occur. Examples are methane in underground gas reservoirs that are hundreds of thousands of years old. Gases stored in bottles. Pressure comes from the gas atoms (with velocity)...

The way I see it, a constant supply of power, say from the engine in a car to its wheels, will cause it to accelerate at a decreasing rate because the kinetic energy the power supplies is proportional to the velocity squared. That makes sense because going faster will cause the car to encounter...

I am trying to wrap my brain around the idea of the cosmological constant, and how it gives the result of an accelerating universe. I have read different explanations for it, and in some it gives me the impression that it is an actual physical force, pushing everything away from everything...

Homework Statement A 48 gram dart is shot vertically upwards from a catapult with a spring constant of 350 N/m. The catapult is initially stretched from the equilibrium point by 21 cm. What is the height above the starting point reached by the dart?Homework Equations KE=PE, rearranging to find...

Assuming a flow can be idealised as incompressible, then can you use the constant pressure assumption ? I just want to get my understanding clear. My problem is the following.Consider a fluid element with volume ##V## and a fixed number of molecules. If the flow is incompressible, then the...

Homework Statement The proper length of a spaceship A is 60 m and the proper length of spaceship B is 120 m. The proper mass of spaceship A is 15000 kg. An observer on Earth watches the two spaceships fly past at a constant speed and determines that they have the same length. If the speed on...

Title should be: Are photon energies constant along null geodesics? [Mentor's note: Title corrected] As I understand it in general relativity the paths of light rays, given by null geodesics, are scale invariant. Is that correct? Now Maxwell's equations in flat Minkowski spacetime are also...

Another silly question... Assuming a surface with no friction in space (you get the idea), I push/kick/give a 1kg block on this horizontal plane a force of 1N. It would start to accelerate in the direction i pushed it with at a rate of 1m/s² forever until another force acted upon it. So far so...

I have some questions about acceleration that I'd like for someone to explain to me. As far as I know, acceleration depends on either change in velocity or change in direction (or both). So if I'm going 1m/s North constantly I'm not accelerating. However, what would be the acceleration if I walk...

Homework Statement What is the magnitude of the electric field due to a 6.0 x 10-9 C charge at a point located 0.025m from the charge? The charge and the point in question are located underwater (κ(water) = 80). Homework Equations I know that E = magnitude of electric field = kq/r2, where k =...

Hi. I was just curious about the current value of the cosmological constant. My astrophysics class lecture notes say on the order of 10^-122, but the Wikipedia article says 10^-35 s^-2. Could someone explain where the 10^-35 s^-2 value comes from? Thanks!

Hi there, I am confusing on the statement that we have classical physics when Planck constant approaching zero. I search the similar topic in Physics Forums and I saw that most of the answers refer to the size effect. It argues that when we measure something in the scale of meter comparing to...

Why cosmological constant term ##\Lambda g_{uv}## in Einstein equation is proportional to ##g_{uv}##. Why it is even proportional to ##g_{uv}## in spacetime of MInkowski?

Homework Statement Consider the wavefunction ##\Psi (x, t) = c\ \psi (x) e^{-iEt/ \hbar}## such that ##\int | \Psi (x, t) |^{2} dx = 1##. I would like to prove to myself that the normalisation factor ##c## is a real number. Homework Equations The Attempt at a Solution ##\int | \Psi (x, t)...

Homework Statement A speeding car has instantenous velocity of 1 m/s when a stopwatch reads 10 seconds. It has constant acceleration of 2 m/s^2. What is the cars speed when it reaches the stopwatch reads 12 seconds. Homework Equations x= (Vinitial)(DeltaT) + 1/2(a09deltaT)^2 I think this is...

Homework Statement An Indy 500 race car's velocity increases from 4m/s to 36m/s over a 4 second time interval. What is its acceleration? 4m/s is the initial velocity, 36 m/s is the final velocity, and time is 4 seconds. Homework Equations final velocity = initial velocity + (acceleration x...

Homework Statement Converting Hubble's constant in SI units of s-1 into kms-1 Mpc-1 (kilometers per second per megaparsec) Number given is 2.31 x 10^-18 s-1. Homework Equations H = v/d (where H is Hubble's constant, v = velocity and d = distance) The Attempt at a Solution I can see how you...

If the speed of light is constant in any inertial frame then how do we measure a red shift or blue shift or why?

Hi guys and gals. I have a constant current welder. 150 Amps DC/ 230 Amps AC output. There is no provision for measuring output current when the machine is welding. I'm thinking of adding a shunt to either the work lead or the return lead. I don't know what size and rating I need. The input...

Homework Statement A molecule is a harmonic oscillator, and has a fundamental frequency of 1000 cm−1 and a reduced mass of 10.0 amu. From this, determine the magnitude of the force constant, and express it in units of aJ ˚A−2 (atto joules per angstrom). Homework Equations ω=√(k/mr) The...