Energy Definition and 999 Threads

I still don't get this and most answers all over kind of miss the point and just kind of recite without really explaining. Here's the dilemma. Yes, kinetic energy grows exponentially with speed. So a 1kg object changing from 0 to 1m/s increases by .5J. And from 4 to 5m/s increases from 8J to...

Included a diagram as well... forgive me... I cannot seem to 'uninvert' the attached picture final velocity is zero if we set the lowest point that the mass reaches as zero, then the final height is zero let H be the 'extra' length that the spring reaches over and above the initial stretch...

Hi I have a problem with task c) For the Poynting vector ##\vec S## and the energy density ##\omega## I got the following: $$\vec S= \frac{1}{\mu_0} \frac{4 I_0^2}{c \varrho} \frac{t}{c^2 t^2 - \varrho^2} \Theta(ct-\varrho)^2 \vec{e}_\varrho$$ $$\omega= \frac{1}{2} \epsilon_0 \frac{4 I_0^2...

[Mentor Note: Two threads on the same basic subject have been merged into this one thread.] Dear PF Forum, It's been a long time since I logged in PF, and I hope everybody is in a good health. Recently I'd like to know what is Kardashev scale type II and III I mean, Type 1: All energy from...

TL;DR Summary: I've done a torque calculation but as I'm new to this I would appreciate if someone could confirm my answer so I know I'm doing it right. The energy it would take to rotate a 10 mm cube weighting 7.5 grams 180 degrees in 0.001 seconds. To simplify it I didn't include drag or...

How to calculate the kinetic energy of an object propelled by a magnetic field. For example I have 2 magnets face to face in opposition. Each magnet is a N42 Neodymium cube dimensions 10, 10, 10 mm they are in free space with no interference. The maximum pull strength is 4.7 kg. If I were to...

Using the above equations and the given information, I get ##k=2.48*10^-4## 2.47∗10−4max=7.56∗10−5##Vmax=7.58*10^-5## and ##total energy=8*10^-6 joules##. My answer is clearly the wrong order of magnitude. The book answer key says 400 joules. My calculation for total energy was...

Observational Assessment of Changes in Earth’s Energy Imbalance Since 2000: 2024 Added greenhouse gases are supposed to be decreasing the OLR.

Could the rotation of tires be used to generate electricity and lengthen range?

i just watched this: and now im wondering, jsut as when the atom bomb converts mass into energy and we can measure it in force and heat and electromagnetic radiation of various wavelengths, obviously just grams, but of what? what particle would we say is representing the 99% of a proton's...

In statistical physics, in a two level system, I'll give an example to show what I am talking about: situation 1) energy 0 and energy E situation 2) energy E/2 and energy -E/2 Are these two situations equivalent? Computing the partition function for both of them it seems they are different...

My thinking is that because of the law of conservation of energy, the amount of energy needed to raise an object to a certain altitude has to be at least as much as the amount of energy released by the object if it were to be dropped from that altitude and hit the ground (and all that released...

Hello All, I have some space outside my room which have sunlight all day. The room heats up to very high temperature. Is there any way I could use that heat to cool down my room without using solar panels? Just a thought.

TL;DR Summary: Need some sources for Lagrangian and Hamilton Mechanics. I was looking through some of my physics books, and in one chapter they mentioned Hamiltonian and Lagrangian Mechanics, I thought it seemed pretty useful and looked into it some more. I noticed that these mechanics were...

Physics describes energy in various forms and each with an appropriate unit of measure. I am curious as to what can be said about the 'form' of energy in the universe's first seconds. Online references locate the Big Bang singularity at an estimated 13.787±0.020 billion years ago with the...

I asked Chat GPT this but could'nt get a satisfactory answer. I felt he was making it up as he went along. In principle it should be possible to set up two lasers emitting the same frequency and synchronize them so they are perfectly out of phase so that both beams destructively interfere. I...

The answer says it decreases but shouldn't it increase? according to the kinetic model, KE accounts for particle vibrations. PE accounts for the attractive forces between particles. Since condensation means gas -> liquid, it means the particles become closer and hence the attractive forces...

Hi all, I hope someone can help me with this: I am working with wien2wannier to obtain Wannier functions from wien2k calculations, but I am struggling to define the energy window needed for the init_w2w. The outputfind file shows emin = -999.00 eV, emax = 999.00 eV, and efermi = 0.6124 Ry...

Hi For a personal project, I am seeking papers or information on the energy level diagrams (where the y-axis is energy (eV)) for Lithium Nitrite (LiNO2) and di-oxygen (O2). I tried the internet and science direct (www.sciencedirect.com) but to no avail. Any help in this matter would be...

[Mentors’ note: No template because this post was moved from the technical forums. Everything that the template asks for seems to be present in the body of the post] Suppose there is a spring-mass system arranged as shown in my crude drawing. This occurs on a frictionless surface. The spring...

My approach to the problem was to try using Q = cmΔt by rearranging it to solve for Δt=Q/cm. Since the power per person is 70 W, there are 1800 people in the concert hall, and the problem asks for the temperature rise over two hours, I multiplied 70 W×1800 people × (3600 sec × 2) which gave me...

I'm 64. My background prior to 2001 - Aviation, experimental aircraft and aerodynamics, robotics, mechanical and software engineering, disaster recovery. Since 2001 - Human sustainability and global recovery, researching every related sector in depth in order to understand what can now be proven...

no clues

In nature how and where is energy converted to matter, where do the necessary conditions exist, is the process well understood, pure theory, or not understood at all?

For the right hand side I expressed each of the quantities in SI units, $$C \cdot \frac{kg}{A \cdot s^{2}} \cdot m$$ Then substitute newtons in as ##N = kg \cdot ms^{-2}## and we get, $$C \cdot \frac{N}{A \cdot m} \cdot m$$ Using the definition of work as ##J = N \cdot m## and Amperes as...

I am not sure what the context of the question is. I am thinking this question is about light bulb emitting different colour at different temperature. The higher the temperature, the lower the wavelength hence the higher the energy emitted by the bulb so the energy consumption will also be...

Imagine an electric field between two charged plates that is so intense that its energy density is enough to produce real electron-positron pairs. These electron-positron pairs annihilate to produce photons that radiate away. Does the electric field between the charged plates regenerate so...

Hello All, I'm trying to simulate in MCNP the energy response of a PIN diode. To do this, I have modelled a "slab" of silicon in an epoxy case at 2cm away from the source and with the F8 tally set to 25keV bin increments to 1MeV, I do as follows: Set the source energy to 33keV Run the...

When there is a probability involved with an energy state, e.g. with partition function, why is total energy the same as average energy (if it is). Just want to make sure - is this just a definition? Thanks

Energy required to evaporate water. Given 3 evaporating scenarios: 1. Glass filled with 50cc of water at 20C; the water is heated to 60C 2. Glass filled with 50cc of water at 20C; the water is heated to 100C 3. 50cc of water at 20C wiped over a large plate to create 50micron thickness layer...

I've mentioned the problem that i'm facing in the question that I've posted. Kindly go through it.

The following is what is written in the book I am reading. The energy required to "push" the mass into the system is $$F\delta z=PA\delta z=PV\tag{1}$$ in which ##V## is the molar volume of the closed system, ##F## is the acting force, ##A## is the cross-sectional area, and ##\delta z## is...

Imagine a projectile with density p, initial velocity v0 and initial stagnation pressure = 0.5p{v0}^2 being fired into the gas chamber with a final gas pressure given by Pg = nkT, for n being the final number density before (at max pressure of gas) and T the corresponding temperature of the gas...

I have a thought experiment in mind. Crudely speaking, the second law of thermodynamics implies that there is only a finite amount of change possible in the universe. Once this limit is reached, no more change can occur. The key thing here though is reversibility. If changes were reversible...

Let me start by saying the idea isn't mine at all. It's actually somewhat usual within Science Fiction works. Maybe one of the most popular appearances of the concept is the videogame Stellaris where there is commerce with aliens so a universal currency is very convenient. In economics, money...

The answer from the textbook is: Use energy conservation ## \frac{1}{2}mv^2 + \frac{1}{2}I_{cyl}w^2 = mgh_{cyl} ## ## \frac{1}{2}mv^2 + \frac{1}{2}I_{sph}w^2 = mgh_{sph} ## Subtracting the two equations, eliminating the initial translational energy, we have: ## h_{cyl} = \frac{v^2}{g}...

Is it possible to solve this without knowing the radius of the cylinder? My initial thoughts were that the energy required to stop it would be the sum of its rotational and translation kinetic energy, but I'm not sure it can be calculated without knowing the radius.

Hi, I love the lectures by David Tong. Usually I can follow his calculations (but I am not yet so far into the lectures...). But one that I just cannot do is the derivation of the energy in (4.16), the expression being ##E = \frac {mk^2} {2 l^2} (e^2 - 1)##, where l is the constant angular...

I'm not quite sure how to apply conservation of string to this problem, so guidance would be appreciated. Normally as long as there isn't a "sub-pulley" I can do the problem fairly easily but this one tricks me up. Thanks

What does it mean to say that Planck's constant is an energy oscillator composed of imaginary and real numbers? This is an expression I saw in a book.

Proof of kinetic energy work done equals a change in kinetic energy in a mechanical system. δW = F.ds W = ∫F.ds W = m∫a.ds W = m∫(dv/dt).ds W = m∫v.dv here if v and dv are in the same direction the change in kinetic energy will be the usual equation. what happens if both are in different...

I was taught to solve this problem by first finding the velocity of the body (of mass ##m ##) relative to the block of mass ##M ##. One way of doing this is as follows: first write $$ {v _{m _{B }}}^{2 }={v _{mx _{B }}}^{2 }+{v _{my }}^{2 } (I)...

I think the angular velocity keep increasing on the plane with friction and the translational velocity keep decreasing due to friction while the total kinetic energy is conserved. When it moves to the frictionless plane, all energy converts to translational kinetic energy and it stop rolling...

Can someone help me by taking a look at the attachment and figuring out where I am making a bad assumption? It's driving me nuts.

I've found some sound and not so sound answers so far. The most interesting is one saying that work is simply one form of energy. The answer used math to support it, but I haven't checked the math yet. Adult ADD, I believe, prompted me to move on instead. Maybe I just have no patience. Idk…

I initially thought about the different forms of energy present at each of the points: Total energy at starting point: PEA+ KEA= mgH at point D: KE_D = 1/2mv2f PED= mgD Energy at point D: PED+ KED D = mgD + 1/2 mv2f because EA= ED mgH = mgD = 1/2 mv2f mg(H-D) = 1/2 mv2f g(H-D) = 1/2...

It is known that while the electric current flows along the wire the energy propagates through the field near that wire (and not by means of electron gas kinetic energy) and the electrons' velocity is equal approximately to 10^[-3] m/s. Meanwhile, the electrons' velocity during the gas...

PF should keep up with the times https://www.livescience.com/planet-earth/nuclear-energy/physicists-solve-nuclear-fusion-mystery-with-mayonnaise :wink:

Q 1) In electric currents, in a battery, the positive charge starts at the negative terminal and gains energy through emf which forces the charge to go to the positive terminal of the battery, with plenty of energy. This voltage is the energy difference between the terminals. For the charges to...

>-Atomic orbitals must be at the similar energy levels to combine as molecular orbitals, said Wikipedia. This is unclear. How do you quantify how "similar" means? I heard electronegative is tied to atomic radius is tied to atomic orbital energy. What are two atoms that would in theory form...