What is First law: Definition and 229 Discussions

"First Law" is a science fiction short story by American writer Isaac Asimov, first published in the October 1956 issue of Fantastic Universe magazine and later collected in The Rest of the Robots (1964) and The Complete Robot (1982). The title of the story is a reference to the first of the Three Laws of Robotics.

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  1. R

    Flow work and the first law of thermodynamics

    Hi Im trying to understand the justification for flow work for a control volumen considering the 1. law of thermodynamics. \[\begin{array}{l} \frac{d}{{dt}}(me) + \sum {{{(e\dot m)}_{out}}} - \sum {{{(e\dot m)}_{in}} = \dot Q + \dot W} + {{\dot W}_{fw}}\\ {{\dot W}_{fw}} = \sum...
  2. F

    How in the world did I get more capacitance? Violating First Law of Thermodynamics?

    Homework Statement Basically we did a lab on charges, capacitors and voltages. We used a 2200uF capacitor and we hooked it up with a 10kΩ Resistor connected in series with a DC Supply. The DC Supply was turned down to 0V and all the other senors were "zeroed" out. Simultaneously, when...
  3. M

    Deriving First Law of Thermo Equations

    Homework Statement This is really just a question that I can't seem to find a good solution for in my book. Basically I'm trying to understand for the first law of thermodynamics how you can derive the equation in term of P1 and P2. I don't understand how to go from PdV to (something)dP. This...
  4. G

    First Law of Thermodynamics - Correct Formulation?

    Homework Statement A gas expands from 1L at 1atm to 3L. Assume P is directly proportional to V. This is a simple question from my second lecture on Thermal Physics, and I have found a way to solve it after my professor made it very confusing in class. My question is more about the...
  5. A

    Special Case of the first law of thermodynamics

    Homework Statement When a system is taken from state i to state f along path iaf in Fig. below, Q = 50.6 cal and W = 20.3 cal. Along path ibf, Q = 36.6 cal. (a) What is W along path ibf? (b) If W = -13.7 cal for the return path fi, what is Q for this path? (c) If Eint,i = 11.1 cal, what is...
  6. A

    What is Force in Newtonian Mechanics & Newton's First Law?

    Is Newton's first law the definition of force in Newtonian mechanics? If not: 1) What is the definition of force in Newtonian mechanics? 2) What is the purpose of Newton's first law?
  7. X

    First law of thermodynamics problem

    Homework Statement An ideal monoatomic gas is held in a perfectly insulated cylinder fitted with a movable piston. Initial pressure is 110kPa, initial temperature is 280K. By pushing on the piston the pressure increases to 140kPa. Find the final temperature. Homework Equations Q=nCdT...
  8. Z

    How Is Internal Energy Affected in the Water to Steam Conversion at 100°C?

    Homework Statement Calculate the increase in internal energy of 1 kg of water at 100 degrees Celsius when it is converted into steam at the same temperature and at 1atm. The density of water and steam are 1000kg/m3 and 0.6kg/m3 resp. The latent heat of vaporisation of water is 2.25 x 106 J/kg...
  9. S

    What Happens When U, Q, and W Are Negative in the First Law of Thermodynamics?

    Homework Statement I am looking into the first law of thermodynamics. But I'm not sure with some parts.Homework Equations dU=Q-W What does it mean when U Q and W are negatives. Also solids with W=0The Attempt at a Solution So the equation will change to -U=-Q+W Does it lose it's internal energy?
  10. M

    Kepler's First Law Mathematical Query

    Hello all! It's been a long summer, and I thought I'd warm up things by going over Kepler's Laws. I've been following the mathematical derivation in Introduction to Modern Astrophysics, and to be honest I am little stumped on a part of it: We have the derived definition of angular momentum...
  11. H

    Thermodynamics Work, Heat, First Law Question

    Homework Statement Consider two pistons of equal cross sectional area joined as illustrated in the following sketch (my rendition): [A|----|B] • Each piston contains n moles of an ideal gas of specific heat cV=(3/2) R. • Each piston's base is fixed, so when the rod joining the piston...
  12. Z

    Trouble understanding Newtons first law and f=ma

    In reading Newtons first law, An object at rest or in motion will remain the same unless acted on by an outside force. also known and understood in Newtons 2nd is Force = mass x acceleration. An object "A" moving at a constant velocity has no acceleration therefor no force. Object "B"...
  13. B

    Newtons first law and inertial reference systems. (noob)

    Hi everyone, Recently i started a self-study in classical physics by reading through some books. In the section that described Newton's first law I stumbled upon something that did not make much sense. The following section of text got me confused. "If the net force acting on a body is...
  14. e2m2a

    Euler's First Law and the Conservation of Momentum

    I know Euler's first law applies to a single body, but can we use it for a system of bodies? Or should we invoke the conservation of momentum to obtain the same result for a system of bodies?
  15. J

    Change in Free Energy in terms of First Law

    I understand why dE=TdS-PdV ...[1] at constant temperature and pressure Also, I see that F=E-TS and therefore dF=dE-SdT-TdS ...[2] and how combining [2] and [3] gives dF=-SdT -PdV QUESTION: shouldn't [1] be expressed as dE=TdS+SdT-PdV i.e if you're going to substitute...
  16. B

    Solve First Law of Thermo Homework: (DT/DV)s = -(DP/DS)v

    Homework Statement First law can be written dU = TdS - PdV where the internal energy U may be written in terms of any two of T,P,V,S. I have to show that (DT/DV)s = -(DP/DS)v where D is partial d, and the subscripts s and v mean hold those constant.. Homework Equations The...
  17. T

    First Law of Maxwell: Exploring Why a Moving Charge Creates a Magnetic Field

    I know that the first law of Maxwell states that every moving charge creates a magnetic field. But, is there an explanation of WHY this happens? Why a moving charge creates a magnetic field? Or this is the kind of law that nobody knows why exist? Thank you
  18. L

    On Newton's First Law of Motion

    This question is probably really stupid but I have to ask. I take a pot of water and stir it. This creates a vortex. When I stop stirring, the water continues spinning before slowing to a stop. But Newton's First Law says that "Every body persists in its state of being at rest or of moving...
  19. G

    First Law of Thermodynamics and automobile

    Homework Statement An automobile battery that is originally fully charged gradually discharges while sitting on a shelf at a constant temperature of 40C, producing no electric work but resulting in a heat transfer of 1000kJ to its enviroment. The battery is then recharged to its initial...
  20. H

    First law of Kepler explained without mass ?

    Hello, I have a question : is it possible to explain the first law of Kepler without any concept of mass ? Kepler's first law states that satellites are moving on an ellipse and the object around which they are orbiting is localized at the focus of this ellipse. As far as I know Newton and...
  21. K

    Enthalpy and Heat: What is the Relationship Between Them and How Do They Differ?

    Concerning the first law of thermodynamics: dE = q - w dE: change in internal energy of a system q: heat added/removed from system w: work on/by the system What is the difference between q (heat added/removed from the system) and H (enthalpy, or heat flow)? Are they analogous to each other?
  22. J

    First law of thermodynamics, q=w for a reversible isothermal process

    according to first law of thermodynamics,q=w for a reversible isothermal process.this means all the energy absorbed is being used to to do the work ,but according to second law of thermodynamics,there cannot be 100% effeciency.please tell where i am going wrong
  23. H

    Questions about forces Newton's Laws (first law)

    Hi, it is known that all bodies moving with a velocity will remain moving with a constant velocity unless a force is applied to a body. (according to Newton's laws). But I thought about this: F = Ma. But if we had a very very very very small object (hypothetically), we could virtually take...
  24. L

    Enthelpy vs Internal energy for first law

    U is internal energy, which is the sum of heat + work done. \DeltaU = q + w -----(1) where w = \Delta(PV) Enthalpy is the internal energy + work done \DeltaH = \DeltaU + P\DeltaV At constant pressure, \DeltaH = q - P\DeltaV + P\DeltaV \DeltaH = q_{p} Where q_{p} is used to...
  25. fluidistic

    First law of thermodynamics situation

    Hi, My mind has been blown up recently when I came across this thread: https://www.physicsforums.com/showthread.php?t=372533. I'd like some explanations about something. Imagine an insulated tank filled with hydrogen and oxygen at 100°C (or greater if possible) and 1 atm. Now a spark...
  26. L

    Newton's First Law Explained: Ball Dropped From Moving Ship

    A ball released from the top of the mast of a moving ship lands at the base of the mast. Explain this according to Newtons' first law. I just know that the first law is that if the net force acting on an object is zero, the object will maintain its state of rest or constant velocity. How does...
  27. L

    Danger of Driving Too Fast on Icy Highway Curve: Newton's 1st Law

    Apply Newton's First Law of Motion to explain the danger in driving too quickly on a curve of an icy highway. I just know that the first law is that if the net force acting on an object is zero, the object will maintain its state of rest or constant velocity. How does it apply to this scenario?
  28. J

    Application of Fick's First law (diffusion problem)

    Homework Statement Molecules with diffusion coefficient of 1.0 x 10^-10 m^2s^-1 are released at a constant rate of 10^10 molecules/s in the middle of a large pool and dffuse away ( assume the 3-dimensional pool is of infinite size). What is the steady state concentration 1 cm away from the...
  29. F

    Gravity and the first law of thermodynamics.

    (Not sure if anyone has asked this before) This idea might be a little vague and I'm sure there is a simple solution but its been annoying me since I thought of it and i'd like to know the answer. If you convert energy into matter then surely matter (with mass) exerts a gravitational pull on...
  30. S

    Confusion with the example of Newton’s first law

    Consider a case where 2 people are in a car driving in a straight line at sufficient speed. At some point the driver takes an abrupt 90 degree right turn and owing to reasons attributed to Newton’s first law the co-passenger swerves into the driver (i.e. to the left). My question is why...
  31. putongren

    First Law of Thermodynamics conversion

    I went to a random page in my physics textbook and came across the First Law of Thermodynamics topic. I am intrigued by the simplicity of the mathematical statement of this law, which is dU = dQ - dW. (dU is the small change in internal energy, dQ is the small change in heat, and dW is the...
  32. D

    What is the true nature of rest according to Newton's first law?

    HI, I have a stupid question but important, Newton;s first law doesn't mention anything about Net force , just that a body that no external forces acts in him, will stay @ rest or with constant velocity ,now my problem is the word "rest", Is a body at rest relative to something Is a body that...
  33. F

    First law of thermodynamics and work done

    Two kilograms of water at 100oC is converted to steam at 1 ATM. Find the work done (in J). (The density of steam at 100oC is 0.598 kg/m3.) a. 4.6 x 104 b. 3.4 x 104 c. 1.2 x 105 d. 2.1 x 104 e. 3.4 x 105 I'ved use the integration holding volume as a variable. However, I don't know why...
  34. fluidistic

    Understanding the first law of thermodynamics in a particular situation

    Imagine the system Table-drop of water on it and air in a closed room, all at the same temperature T. (0°C<T<100°C). After some time the water drop will evaporate. Shouldn't it make the room pressure increase? If so then I can imagine a system where there's no heat input and the system can...
  35. K

    Problem on thermodynamics first law again

    Homework Statement Consider a system consisting of 2.0 mol CO2 (assumed to be a perfect gas) at 298K confined to a cylinder of cross-section 10cm^2 at 10 atm. The gas is allowed to expand adiabatically and reversibly against a constant pressure of 1 atm. Calculate W, Q, ΔU, ΔH, and ΔT when the...
  36. N

    Circular argument in the first law of thermodynamics ?

    According to Caratheodory, the first law of thermodynamics (dE=dQ-dW) could be derived from the definition of heat (dQ=dE-dW), whether this form a circular argument or tautology ? How to clarify the confusion between the first law of thermodynamics and the definition of heat，and capture the true...
  37. R

    Keppler's 1st Law: Examining a Proof

    Homework Statement i am examining a proof of kepplers first law for my conics project and I am a bit rusty on the physics, it begins withe the following line Homework Equations To begin with, we will start off by applying Newton's law of motion and Newton's law of universal gravitation...
  38. C

    Gravity creates energy Violation of the first law of thermodynamics?

    Gravity creates energy...Violation of the first law of thermodynamics? Two Identical metiorites traveling slowly through space happen to be on a vector that will cause them to collide with the earth. One is due to strike the Earth one week after the other. The first one comes in close to Earth...
  39. E

    Thermodynamics - First Law, Work

    [Homework Statement Imagine some helium in a cylinder with an initial volume of 1 liter and an initial pressure of 1 atm. Somehow the helium is made to expand to a final volume of 3 liters, in such a way that its pressure rises in direct proportion to its volume. (b) calculate the work...
  40. B

    First Law of Thermodynamics Question

    Homework Statement The first law of thermodynamics states ΔQ = ΔU + ΔW. What does the ΔQ and the ΔW represent? Homework Equations ΔQ = ΔU + ΔW The Attempt at a Solution I've never seen the equation set up like this before so I'm a little confused. I said that ΔQ is the heat...
  41. A

    Newton's First Law & Constant Velocity Car

    Homework Statement What can be said about a car traveling at constant velocity on a street, keeping in mind Newton's first law? Homework Equations The Attempt at a Solution My first reaction to this question is "But a car is not a particle." Assuming the car is a particle, then it...
  42. M

    Forces and laws of motion worksheet-Newtons first law

    Homework Statement http://go.hrw.com/resources/go_sc/phy/HF2SR042.PDF this is the link to the worksheet I am having trouble with. if anyone could help me out that would be great. i got most of it but have a few questions. Homework Equations fy=sin(angle) x force fx= cos(angle) x...
  43. S

    First law of thermodynamics. Gas expansion

    1.1 kg off air with pressure 10^6 Pa, temperature 125 celciusdegrees, gets to expand until the volume is five times bigger than in the beginning. In every moment of the expansion, the amount of (warmth energy = Q) contributed is one fourth of the work done by the gas. 1 kmol of air weighs about...
  44. T

    First law of thermodynamics rate problem

    Homework Statement consider a room that is initially at the outdoor temperature of 20 degrees C. The room contains a 100-W lightbulb, a 110-W TV set, a 200-W refrigerator, and a 1000-W iron. Assuming no heat transfer through the walls, determine the rate of increase of the energy content of...
  45. A

    Understanding Newton's First Law for Force Tables

    I did an experiment on a force table with pulleys and weights. We were suppose to, through trial and error, find weights and add them on strings that were placed at different angles, so that the ring in the middle would become centered. Attached is the data table. I am suppose to calculate the...
  46. M

    Air Track Experiment: Explaining the Velocity Increase

    I have just done an experiment with a glider on an air track and applied a force to it. Its velocity increased very slightly and was wondering are there any reasons, other than friction, why the velocity could change during motion? Thanks I thought this but i don't know if its right "There...
  47. P

    How do I solve for V in terms of p?

    can somebody help me in solving this problem..thanks.. A gaseous substance whose properties are unknown, except as specified below, undergoes an internally reversible process during which V = (-0.1p + 300)ft cube, when p is in psfa. (a) for this process, find -/ V dp and...
  48. I

    How Does Friction Heating Follow the First Law of Thermodynamics?

    Homework Statement I am trying to understand how the process of friction heating a block as it slides can be explained by the first law of thermodynamics. Homework Equations W_net(net work on object) = change in KE change in internal energy = Q(heat added to system) - W_by (work...
  49. B

    First Law of Thermodynamics and ideal gas

    Homework Statement An ideal gas expands isothermally, performing 3.40x10^3 J of work in the process. a) The change in internal energy of the gas b) The heat absorbed during this expansion Homework Equations \DeltaU=Q-W The Attempt at a Solution a) Since it's isothermally...
  50. H

    Help needed - Newtons first law - particles in equilibrium

    For some odd reason, I'm having no problems with the rest of the exercises, though this one is really annoying as i just can't seem to get it right. Here's a picture of the exercise h t t p://img2.freeimagehosting.net/image.php?4bc2e12442.jpg...
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