Laws Definition and 1000 Threads

We know that ##F=ma## or ##F=ma=m \frac{v}{t}##, so the acceleration is rate of slowing or speeding velocity, then does force changes the momentum ##p=mv## or ##p=Ft##. I'm waiting an answer, thanks!:)

Physical laws ... are they material?! There was an old question about physical laws , where do they come from? as they are considered separated from the material of the universe. Of course I know that they are produced by the human brain or human consciousness (which is material in turn) , but...

I was hoping someone could help out, I am working out a problem with Kirchoff's Laws and cannot seem to get the math to work out properly, at least I think the math is not working properly. I was hoping to run it by someone here. Homework Statement The circuit is as follows: A battery...

Homework Statement lim ( f(x)/(x2) )= 8 [SIZE="1"]x→0 Then what is... a)lim ( f(x) ) [SIZE="1"] x→0 b)lim ( f(x)/x ) [SIZE="1"] x→0 Homework Equations The Attempt at a Solution tried separating the limits (lim [SIZE="1"]x→0 f(x))(lim...

Homework Statement From the attached file using Kirchoff's laws prove that V [SIZE="1"]AB = V [SIZE="1"]AD and that i[SIZE="1"]1 = i/2 Homework Equations V1 + V2 + V3 +... Vn = 0 (The sum of the voltage applied and dropped across the components is zero. i1 + i2 = i3 (The sum of the branch...

Is it accepted as theoretically possible that there could be an infinity of universes with totally unrelated (or possibly related) laws governing their processes? I don't mean the different universes to have different initial (or practically initial) conditions but to have their own set...

Homework Statement 10.0km [N] + 5.0km [E15S] Homework Equations Cosine Law The Attempt at a Solution If you draw it out you see that 10km is 90 degrees north. From the 10km end, you do E15S for 5km. Therefore, a = 10km, b = 5km, c = ?, C = 90 - 15 = 75. Therefore: c^2...

THIS ISN'T THE SAME AS MY PREVIOUS QUESTION ALTHOUGH IT HAS THE SAME TITLE Homework Statement The Moon is satellite of Earth with a diameter equal to a quarter of Earth's diameter and a mass equal 1/81 of Earth's mass. The period of the moon's rotation about the Earth is 27d 7h 43.1 min...

Homework Statement An imaginary planet has a diameter twice that of our earth. The planet has one moon with an orbital radius of 5.0x10^7 km and orbital period of 10 Earth days. Determine the strength of the gravitational field at the surface of the planet. Radius of Earth = 6.38 x 10^6m...

Why are Newtons law of universal gravitation, F=G\frac{m_{1}m_{2}}{r^{2}} and Coulombs law, F = K_{e}\frac{q_{1}q_{2}}{r^{2}} inverse square laws? I understand why they are inverse because the force decreases with distance but why is the distance, r, squared? Thanks AL

The world seems to me to be rather arbitrary. I don 't know if people feel the way I do. Scientists apply for government grants to gather data, and conduct experiments. Some scientists look at the data, and write down equations. If those equations are sufficiently fundamental, then some...

I don't understand this. The Entropy described in Isaac Asimov's " The last Question " is what i always tought to be the 2nd law of Thermodynamics. Now if this is correct i just can't understand how such entropy is possible with the first law of thermodynamics. I obviously know that i am wrong...

a) A shirt left on your bedroom floor is still there after 2 days. (Newton's 1 law) b) You run into your friend while ice-skating, & you both fall in opposite directions. (3rd law) c) The horse you're riding trips on a tree stump & stops quickly, & you fly forward. (1st law) d) A baseball...

Homework Statement Hydrogen gas is collected over water at 25°C. The atmospheric pressure in the room is 745 mm Hg and the volume of gas in the container is 43.5mL. The vapor pressure of water at 25°C is 23.8 mm Hg. Determine the volume the gas would occupy at STP. Homework Equations...

Homework Statement For a birthday gift, you and some friends take a hot-air balloon ride. One friend is late, so the balloon floats a couple of feet off the ground as you wait. Before this person arrives, the combined weight of the basket and people is 1200kg , and the balloon is neutrally...

I've always found it pretty amazing that human beings can understand the rules that govern the universe we live in, but is there a fundamental reason as to why they are comprehensible at all? Do they have to be rooted in logic? If it's just something that is unknown, that's a perfectly...

Dear All, I need help on proving: According to Pauls Online Notes, we let ε > 0. Since http://tutorial.math.lamar.edu/Classes/CalcI/LimitProofs_files/eq0075M.gif, there's a [PLAIN]http://tutorial.math.lamar.edu/Classes/CalcI/LimitProofs_files/eq0076M.gif such that I...

I know from linear algebra that you can take two things, and if they are equal to each other then you can simply substitute different variables to develop a proof of a different statement. For example take, w = a w = z + k therefore proof would posit that a = z + k But my dilemma lies in what...

Homework Statement Find the pressure and temperature when given the following data on helium gas: Volume (V) = 0.10 m^3 ** Helium mass (m) = 4.0 amu ** Number of atoms (N) = 3.0 x 10^24 Assuming PV = 1 then P=1/V then Pressure = 1.0 / 0.10m^3 = 10Pa Homework Equations PV = NkT...

I've been lurking on PF for awhile now, but I reckon I'd benefit by actually trying to participate in the discussion and by asking my own questions once in awhile so, Hi all! In my second year I took a module on Classical Mechanics, and one of the things we covered was the Coriolis Theorem...

How would you show mathematically that Newton's laws, when taken as given, always yield a motion and that this motion is always unique (given initial positions/velocities) for arbitrary systems?

Homework Statement 1. For the system shown below use Newton’s Laws to clearly derive an expression for the acceleration of each mass and the tensions in the cord. The coefficient of friction between m1 and the incline is 0.100. The mass m1 is 3.00 kg, m2 = 8.00 kg, and θ = 35.0°. The...

I have my first physics exam coming up in January. To study I've been doing the past exams from the previous years, but there were are a few questions that I wasn't 100% sure about. I'd be greatful if anyone could tell me if my answers are correct or not :smile: 1) Which of the following...

Laymen here. I have been told that the motion of particles at the quantum level are random. If this is not true please elaborate. Whether this is the case or whether there is a pattern waiting to be discovered, isn't it true that the world at the quantum level is still governed by...

Homework Statement A 880 N crate is being pulled across a level floor by a force F of 385 N at an angle of 27° above the horizontal. The coefficient of kinetic friction between the crate and the floor is 0.25. Find the magnitude of the acceleration of the crate. Homework Equations...

Homework Statement A small wooden block, of mass M, lies in the middle of a horizontal table of length L and height h above the floor. The coefficient of kinetic friction between this block and the surface of the table is μ. A bullet, of mass m, is shot with a horizontal velocity into...

Hello PF community! I'm having trouble with what strikes me as an inconsistency within conservation of energy, conservation of momentum, and the four-momentum invariant equation (E2-p2c2 = m2c4). For the sake of this question, I'll be using non-relativistic mass--i.e. mass is the same in all...

Do you have any idea about ridiculous laws? These are the laws which makes no proper sense. Usually the purpose of making laws is to improve the disciplined level in society. Some of the really ridiculous laws are. 1.You may not have an ice cream cone in your back pocket at any time. 2. It is...

The first law of motion says that it takes force to accelerate something. The second law of motion says that F=ma. So now my teacher says that the first law is for inertial reference frames, while the second is for non-inertial reference frames. This really annoys me because I don't...

Homework Statement Calculate the value of the current through the 12V battery shown in figure (attached). Homework Equations V = IR I1 = I2 + I3 The Attempt at a Solution I've calculated the current for the left hand loop, see below: Loop 1: E_1- E_2- V_1- V_2=0 E_1- E_2=...

Newt Gingrich: "Child labor laws are stupid" http://www.latimes.com/news/politics/la-pn-gingrich-child-labor-20111121,0,6466282.story Please tell me this is a parody or I'm misunderstanding him or SOMETHING. Cause the way I read it, he wants to repeal CHILD LABOR LAWS.

Homework Statement What must the emf ε in the figure be in order for the current through the 7Ω resistor to be 1.79A ? Each emf source has negligible internal resistance. Homework Equations V=IR Kirchoffs junc and loop rules The Attempt at a Solution I put that the outer...

Homework Statement Find the wavelength of an electron which is traveling at 4.35*10^6 m/s. Homework Equations p = h/λ p = mv E = hf E = 1/2mv^2 The Attempt at a Solution I know this can be easily solved using the momentum equation and De Broglie's law like this: mv = h/λ...

In Introduction to Mechanics by Kleppner, the section on Newton's third law says that the third law is not only a physical principle but is also a logical necessity for the first two laws to make sense. I don't quite get this. These statement precedes an experiment regarding an object in a...

A mass is hanged by 2 cables, the first makes 30° with the ceiling while the second makes 60° with the ceiling. Find the attached mass if the first tension is 24.5 N and the second tension is 42.7 N. my way: T1=24.5N θ=30 T2=42.7N θ= -60 m=? m=Fnet/a the ans should be (m=5.017 Kg)

Has anyone discovered the laws governing or explaining the passage of Time? Shouldn't there be laws for that as well? In addition to the laws that explain the fundamental forces and how they interact, shouldn't there be laws that govern/explain how the universe got from the big bang to here?

i can understand the weak large number law however, what does strong large number law mean? i cannot see the difference between the two ps: i do physics, not maths

Conservation Laws - Finding angle ? Homework Statement Having trouble with question 2, a) - See below Homework Equations The Attempt at a Solution Which conservations laws am I suppoe to use to figure this out? THanks!

1.) does a stationary charge in a gravitational field radiate (as per the principle of equivalence)? 2.) why have we been advancing from seemingly less intelligent species to a more intelligent one? what is its physical significance (besides intelligence corresponding to complexity) ? why do...

hello, we have learned that according to the laws of thermodynamics that the efficiency of any machine should be less than one because of the passive components in it. in an electric heating machine all the input electrical energy is converted to heat. Does this make the electrical heater as an...

Homework Statement "A bicyclist can coast down a 5° hill at a constant 7.0 km/h. Assume the force of friction (air resistance) is proportional to the speed v so that Fair = cv." (a) Calculate the value of the constant c. (b) Calculate the average force that must be applied in order to...

The other day, as I was struggling through my quantum mechanics text, I realized that the only physical laws presented in the text were the four postulates of QM, the last of which is Schrodinger's equation. These are presented around page 150. The first 150 pages establish the background needed...

Homework Statement A turn in the road with a radius of 30m is banked at an angle of 40 degrees. If \mu=.75, what is the minimum and max speed a 1200 kg car can travel without sliding off the turn. Homework Equations F=ma, Mv^2/R, Fw = mg The Attempt at a Solution Alright, so...

In "The Algebra of Grand Unified Theories" http://arxiv.org/abs/0904.1556" john Baez (see page nb 9) shows how the conservation of eigenvalues (T3 isospin) appears if there is an intertwiner between the representation spaces of the symmetry group. I discovered intertwiners for the first time...

Homework Statement A 54 kg woman is ice-skating toward the east on a frictionless frozen lake when she collides with a 79 kg man who is ice-skating toward the west. The maximum force exerted on the woman by the man during the collision is 160 N, west. Take east to be the positive direction of...

Are physics laws (even the laws) mathematical models of reality? Or they describe reality as it is? Are those laws just models, like for example a population's growth mathematical model (just an example that I remembered)? A maths teacher told me that in physics everything are...

Homework Statement Prove that the transformation law \Gamma^{\sigma '}_{\lambda '\rho '}=\frac{\partial x^\nu}{\partial x^{\lambda '}}\frac{\partial x^\rho}{\partial x^{\rho '}}\frac{\partial x^{\sigma '}}{\partial x^{\mu}}\Gamma^{\mu}_{\nu\rho}+\frac{\partial x^{\sigma '}}{\partial...

Homework Statement People who are angry sometimes say that the feel as if they will explode. If a calm person with a lung capacity of 3.5L and a body temp of 36C gets angry, what will the volume of the persons lungs be if their temp rises to 39C. Homework Equations V1/T1 = v2/T2...

Homework Statement Find : a) acceleration of 1 kg, 2kg and 3 kg blocks and b) tensions T1 and T2 Note: In the figure, 1, 2 and 3 represent the masses of respective blocks in Kg. T1 and T2 represent tension in strings Homework Equations Newton's laws and constraint equations...

What is the magnitude of the force F (assumed horizontal) required to push the block up the plane at a constant speed? Take the coefficient of kinetic friction to be 0.25. Block is 75 lb I used Ff= mewN and found Wparallel Did Ʃ=ma Fapp-Ff-Wparallel= ma but i keep getting wrong answer