# 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. ### I Application of the first law of thermodynamics

In Halliday's physics book, there is an example of the first law of thermodynamics that shows its application. The figure below explains this example: Here is a question, if the element alone is chosen as the system, doubts arise in the first law, because in this system, Q<0 (because heat is...
2. ### B Newton's First Law -- Mistranslated for 3 centuries

https://www.scientificamerican.com/article/mistranslation-of-newtons-first-law-discovered-after-nearly-300-years/
3. ### Newton's First Law to explain Washing Machine Spin Cycle

I truly am not sure. I assume it is that because everything has inertia, an a tendency to remain in a constant state of motion, when the clothes are quickly spun around they cannot remain in a constant state of motion (of either rest or constant velocity), but the water is "pushed"/spun out of...
4. ### Academic First Law Of Thermodynamics Problem

Hi there. I have a problem solving above problem. How can I move on with my solution? It seems to me that I have proper approach but I'm just stuck with the energy equation ;/ Part of solution below:
5. ### B Question about magnetizing and the First law of Thermodynamics

I've been learning a lot about life from Internet searches and I do hope this isn't too basic of a question for you gurus. If I had two pieces of iron next to each other with a pea in-between and two pieces of cobalt with a pea in-between. Then I magnetized the four pieces of metal by brushing...
6. ### Newton's First law of motion -- Boy jumping vertically on a moving train

I'm not sure if my answer is correct but I think the answer is false. Thank you for your help :) -sun1108
7. ### B Is Newton's first law of motion applicable when walking?

Is Newton's first law of motion applicable when walking?
8. ### Question on First Law of Thermodynamics (Paramagnet)

For the first part, I have expressed it in the following differential form- dU= delta (Q) + BdM Now for the second part I am having major confusion. I know that B corresponds to P and M corresponds to V as generalised force and generalised displacement respectively for a Paramagnetic substance...
9. ### Engineering First Law ΔU = Q − W | Understanding & Math Example

Is the non flow energy equation just the first law equation Im writing about the first law i write the definition and that the first law equation ΔU = Q − W or can be written as Equation: Q - W = (U2 - U1). Then gave a math example using Equation: Q - W = (U2 - U1) to show the first law...
10. ### Finding temperature change, thermodynamics first law

So I calculated the final and initial pressures using the given eqns, ended up with the final pressure of 96629 and initial pressure of 62639. Then I used the PV=nRT eqn to calculate the final and initial temperatures. T=P*V/(n*1.5*R). I got an initial temperature of 81.79 and a final...
11. ### Engineering Why is the first law of thermodynamics useful in developing these equations?

why it is first law of thermodynamics useful in developing the non-flow energy equation and steady-flow energy equation. First Law Equation (FLE) = 1 1.1 Non-Flow Equation = 2 Steady-Flow Equation = 3 Specific Entrapy of Steady-Flow 4 Mass Flow 5 I understand (i think) but can't explain...
12. ### The first law of thermodynamics for open systems

Please see enclosed my calculations for parts 1-3. I am stuck on the final part of of a 4 part question, any help or guidance would be very much appreciated, thanks.
13. ### First law of Thermodynamics and energy conservation

Hi PF! I don't understand the sentence: on one side says the energy is preserved, and, at the end, the total energy of the system will change if ##W## or ##Q## is added: ##\Delta{U}=Q+W##. Greetings!
14. ### First Law for a Eulerian non-inertial system

Hello to everyone, I'm trying to demonstrate (a) starting from a Lagrangian system. However I have found some difficoulties so I hope you can help me. First of all, I'm going to illustrate a demonstration I found of the First Law, for a Eulerian -inertial system...
15. ### Engineering First law of a thermodynamic system

After crossing out all the variables which I think equals 0 in the equation, I was left with: ∆PE + ∆U = Qin mg (0.2) + ∆U = 300 10*9.81*0.2 - 300 = - ∆U = -280J This was the answer I derived. However, the correct answer was supposed to be 123.3J. Please can someone explain to me how to get...
16. ### First law of thermodynamics and the work done on a system

The first law of thermodynamics states that the change in the internal energy of a system equals the net heat transfer into the system minus the net work done by the system. In equation form, the first law of thermodynamics is ΔU = Q − W. in the mathematical expression of the first law of...
17. ### Newton's first law and a body on an infinite and frictionless road

Hi everyone! I have started to study physics this month and I got to the Newton's laws. According to Wikipedia, the first law is: This definition made me wonder: If there was, let's say, a fictional road, infinite long and frictionless, and a body would move in constant velocity over it, could...
18. ### Question about the first law of thermodynamics

In thermodynamics, the internal energy (U) is the function of the volume (V) and temperature (T), U = U (T). Therefore, according to the mathematics, dU = π dV + Cv dT, where π is internal pressure and Cv is the constant volume heat capacity. Meanwhile, according to the 1st law, dU = δ w + δq...
19. ### Does the First Law of Thermodynamics Allow for Heat Generation During Stirring?

Consider a system composed of a gas+stirrer at state 1, Work is done on the system by a rotating shaft, the stirrer activates high speed generating a significant amount of heat. The system is undergoing a process because the set of measurable properties to define its state are changing, If I...
20. ### The Confusion of Weight and Mass in Physics Education

In material introducing Newton's First Law to students, we sometimes see a supplementary statement to this effect: in addition to changing the velocity of an object, forces can distort its shape. But surely here two different situations are being conflated: (1) the effect of a single force on...
21. ### B Black holes and the first law of thermodynamics

The first law of thermodynamics states that matter can only be transferred from one state to another, and cannot be truly destroyed. What happens to matter consumed by a black hole? What happens to it and where does it go? Does the first law still hold true?
22. ### Definition of Heat and the First Law of Thermodynamics (discrepancy?)

Zemansky defines Heat as : When a closed system whose surroundings are at a different temperature and on which diathermic work may be done undergoes a process, then the energy transferred by non mechanical means, equal to the difference between the change in internal energy and the diathermic...
23. ### Is Newton's First Law a conservation law?

I'm thinking through a few basic things - hopefully in a new way. One thing that struck me is that momentum (mv) and energy (e.g. 0.5mv^2) can be conserved but velocity is not. For one thing, velocity is relative, of course. I'm wondering whether there's a quantity a bit like velocity but not...
24. ### Energy and first law thermodynamics help

Hey guys, Have a thermodynamics exam coming in the next few days up based on the following topics. Energy and first law, Thermodynamic properties, First law: closed systems, First law: open systems/specific heat. When I have taken a look at the past exams it has been all calculations and...
25. ### 1st law of thermodynamics with chemical reaction?

##dU = dw + dq ## vs ##dU = dw + dq + µdN## Which equation do we apply to a closed system involving chemical reaction? According to textbooks, the first equation holds for any closed system in the absence of fields and kinetic energy. However, later chapters use the second equation for...
26. ### Joule's first law - kinetic energy of electrical current

Dear Sirs, If I take this explanation as being true "The heat is generated on the microscale when the conduction electrons transfer energy to the conductor's atoms by way of collisions." So a "current" must have a quantum of kinetic energy going into the conductor (resistive element) and a...
27. ### Why doesn't Q=0 instead of Q=W if T=constant in first law?

My understanding of heat is the energy transferred as a result of temperature imbalance between systems. If two systems at different temperatures are in contact with each other, a temperature change for both systems and an energy transfer Q is occurring. It is known that Q=W for a closed...
28. ### Experiment on Newtons First Law

I am wondering if anyone knows of a good resource to see Newtons first law in action. For example, a block being pulled by increasing force until it moves?
29. ### Steady Flow, Thermodynamics First Law

Homework Statement 12kg of a fluid per minute goes through a reversible steady flow process. The properties of fluid at the inlet are p1 = 1.4bar, ρ1 = 25kg/m3, C1= 120m/s and u1= 920kJ/kg and at the exit are p2= 5.6bar, ρ 2= 5 kg/m3, C2= 180m/s and u2 Homework Equations u1 + P1V1 + (C1)2/2 +...
30. ### First law of thermodynamics, mass/energy in the Universe

Ok, so just a quick question, first law of thermodynamics basically states that matter cannot be created nor destroyed aka it can only change states and turn into energy or vice versa, the second law states that, IIRC, for perfect isolated systems entropy remains constant but for our universe...
31. ### Question about thermodynamics first law

I know that dS=dQ/T for reversible process, is dU=TdS-PdV for reversible process only?
32. ### Kirchhoff's First Law to solve a circuit with 2 loops

Homework Statement I've recently watched a video which explains Kirchhoff's first law however, I'm not sure about his calculations. I got the same answer just wanting to make sure I am doing it right. the guy wrote L1: -75I2 +3V=0 ⇒ I2= -3/-75=0.04A He calculated L2 like -12V -125I3 +75I2=0 ⇒...
33. ### Newton's first law of motion and Inertial Systems

I have just begun my journey in Classical Mechanics with the book "An Introduction to Mechanics" by Kleppner and Kolenkow. I find myself stuck at Newton's first law. The book presents Newton's first law as follows: "Newton's first law is an assertion that inertial frames exist." The book also...
34. ### Mathematical model of Newton's first law

Is there a mathematic model for the first law of dynamics? If no, do you think that this law can be modellized with maths?
35. ### Newton's First Law problem -- Conceptual question about KE

I have come up with a bit of a problem in my head regarding Newton's first law. If any of you could help me solve it that would be much appreciated. So if you throw a tennis ball (or any object really), and you throw it into an infinite expanse of nothing but void, it will travel forever, or...
36. ### Why do we have Newton's first law

Hey guy! I know how Newton's first law said but i can't understand why. So can you pleas help and tell me why. Thank you!
37. ### Confusion regarding the First Law of Thermodynamics

Is forcing a closed system to expand (e.g. by pulling out a piston), causing it to cool, work done to the system or work done by the system? I assume it was work done to the system, but that means the first law of thermodynamics formula no longer balances if you assume an adiabatic change...
38. ### A Non-locality and The First Law of Thermodynamics

I'm sure I read somewhere in my physics books that non-locality is required in order to maintain the integrity of the 1st Law of Thermodynamics. Is that correct? If so, that seems to require one or more additional spatial dimensions via which the total amount of energy is maintained. What...
39. ### How to apply the First Law of Thermodynamics to this problem?

Homework Statement A spring (k = 500 N/m) supports a 400 g mass which is immersed in 900 g of water. The specific heat of the mass is 450 J/kg and of water is 4184 J/kg. The spring is now stretched 15 cm and, after thermal equilibrium is reached, the mass is released so it vibrates up and...
40. ### Rearrangement of the First Law of Thermodynamics

For class we have been asked to show how the first law of thermodynamics dU=dQ+dW can be shown to be dQ=(CV/R)*VdP +(Cp/R)*PdV I have an answer, but am hesitant to say it is a final answer. I will admit that while doing the problem I had trouble following what I was doing. Hence my...
41. ### First law of thermodynamics: why some equations can't be used

Homework Statement A cylinder fitted with a frictionless piston contains 5.0×10-4m3 of an ideal gas at a pressure of 1.0×105 Pa and temperature of 300K. The gas is then (i) heated at constant pressure to 450K, and then (ii) cooled at constant volume to the original temperature of 300K. The...
42. ### Kepler's first law for any body

I was just wondering, what if an object is placed in our solar system, will it revolve around the sun? If yes, will it have a centripetal acceleration too?
43. ### Calculating Final Temperature of Two Solids in Thermal Contact

Homework Statement 55. Solid A, with mass M, is at its melting point TA. It is placed in thermal contact with solid B, with heat capacity CB and initially at temperature TB (TB > TA). The combination is thermally isolated. A has latent heat of fusion L and when it has melted has heat capacity...
44. ### Does Newton's or Galileo's first law depend on gravity?

Does Newton's or galileo's first law depends on gravity ? Galileo said that ball rolling on a downward sloping plane speeds up while ball rolling on upward sloping plane slows down therefore he concluded that ball remains with constant velocity(unaccelarated) on a horizontal plane here...
45. ### Frame of reference in which Newton's first law is not valid

Newtons first law of motion depends on frame of reference So what are some examples , which shows that in this frame of reference F = 0, but a is not equal to zero or vice versa.
46. ### Mathematical Proof of Kepler's First Law of Orbits

Hello friends (I hope :biggrin:), For a maths project I am working on, I need to be able to prove the equation for an elliptical orbit, related to Kepler's first law: and p = a(1-e2) (or should be as p can be replaced by that value) Where: r = distance from sun to any point on the orbit p =...
47. ### Newton's First law: Barrier on large transport trucks

Homework Statement Explain why large transport trucks have a hard steel barrier between the load and the driver's cab. Consider Newton's first law in your answer. Homework Equations no equations required.The Attempt at a Solution According to Newton’s first law, if no net force acts on an...
48. ### Understanding Newton's First Law & Safety Measures for Roller Coaster Rides

Homework Statement Homework Equations no formula's required The Attempt at a Solution please explain if these answers are correct, thanks 34. Large transport trucks have a hard steel barrier between the load and the driver’s cab In order to protect the driver and prevent injury. According...
49. ### Thermodynamics First law ideal gas question

Homework Statement We have 0.0008 Kmol of an ideal gas are expanded from V1 to V2 v2=3V1 process is reversible and T/V=Constant if the work obtained by this expansion is 9.4 KJ find the initial temperature R=8.314 KJ Kmol-1 Homework Equations PV=nRT possibly T/V = T/V The Attempt at a...
50. ### Newton's first law, forces, charges

Homework Statement Two uniform masses of .260kg are fixed at points A and B. Find the magnitude and direction of the initial acceleration of a uniform sphere with mass 0.01kg released from rest at point P that is acted on the gravitational forces of attraction from spheres A and B. The diagram...