# What is Energy transfer: Definition and 155 Discussions

In physics, energy is the quantitative property that must be transferred to a body or physical system to perform work on the body, or to heat it. Energy is a conserved quantity; the law of conservation of energy states that energy can be converted in form, but not created or destroyed. The unit of measurement in the International System of Units (SI) of energy is the joule, which is the energy transferred to an object by the work of moving it a distance of one metre against a force of one newton.
Common forms of energy include the kinetic energy of a moving object, the potential energy stored by an object's position in a force field (gravitational, electric or magnetic), the elastic energy stored by stretching solid objects, the chemical energy released when a fuel burns, the radiant energy carried by light, and the thermal energy due to an object's temperature.
Mass and energy are closely related. Due to mass–energy equivalence, any object that has mass when stationary (called rest mass) also has an equivalent amount of energy whose form is called rest energy, and any additional energy (of any form) acquired by the object above that rest energy will increase the object's total mass just as it increases its total energy. For example, after heating an object, its increase in energy could be measured as a small increase in mass, with a sensitive enough scale.
Living organisms require energy to stay alive, such as the energy humans get from food. Human civilization requires energy to function, which it gets from energy resources such as fossil fuels, nuclear fuel, or renewable energy. The processes of Earth's climate and ecosystem are driven by the radiant energy Earth receives from the Sun and the geothermal energy contained within the earth.

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1. ### Energy transfer/loss in catapult

TL;DR Summary: In a classic catapult the arm usually meets a cross brace that stops it and helps define the exit angle. This seems a bit wasteful. I have been thinking about making a small catapult for my sons class. In a classic catapult the arm usually meets a cross brace that stops it and...
2. ### Kinetic energy transfer from a rotating body in an inelastic collision

The cylinder in question would have a moment of inertia of ~1.67kg*m² and rotational KE of 2.058J. At the point of impact also, assuming the body hits the sphere at a 90deg angle after traversing 90deg of displacement, it should(?) exert a force of 1.31N - enough to give an acceleration of...
3. ### Kinetic energy transfer from shockwave to secondary body

I would guess that by multiplying the pressure exerted by the shockwave on the body, and then the resulting force - here ~69 Newtons - per the distance the shockwave passed through when traversing body A, I could get the work done but I’m not sure if it’s that easy and whether or not I should...
4. ### Dimensional Analysis: Forster Energy Transfer equation

I'm trying to calculate Forster's Resonance Energy Transfer rate, but I just can't seem to get the units right. I'm trying to teach my students how to calculate them. Here is the (relatively) original technical note of FRET equation, made by the original author...
5. ### I Energy Transfer Between Inertia Wheels

Been 20 years since college physics. I have a problem where there are basically two inertia wheels on separate shafts coupled by a clutch. One wheel is spinning and the other is at rest. The clutch engages and connects the shafts. What's the final rpm of both wheels? I'm struggling to find a...
6. ### I Energy Transfer Through Materials

Hi and thanks for taking the time to read my question. So, if i take an element and place it on top of another element and heat it, will the heat energy pass through the first and charge the other or it'll melt both elements? Thanks!
7. ### Energy transfer and conservation cases for pendulum motion and EM wave

Let me ask a very primitive question. To and fro motion of pendulum under gravity tells us potential energy + kinetic energy = const. At the top points potential energy: max kinetic energy :0 At the bottom point potential energy: 0 kinetic energy :max EM wave is usually illustrated as...
8. ### How does mass influence energy transfer?

Summary:: How does mass influence energy transfer? Can someone help me with this question? Thanks!
9. ### Unraveling the Mystery of Work Done & Energy Transfer

I was reading the chapter kinetic energy and work where I saw a derivation in which it was proved that work done=change in kinetic energy, so i understood from this derivation that work done is energy transfer by means of force but in this book kinetic energy is introduced earlier so as to find...
10. ### B Why does energy transfer during collisions?

We were doing an experiment where you put a tennis ball on top of a basket ball, and release to the floor. The tennis ball goes flying high and the basketball hardly bounces at all. We also measured the initial bounce of each independently. We're talking about impact and momentum, energy...
11. ### A One way vibrational energy transfer

https://www.sciencedaily.com/releases/2019/04/190403135011.htm Yale University folks have come up with a new technology which they say can make sound as well as heat flow in one direction only. This is done by using a "standard cavity - optomechanical interaction to produce robust nonreciprocal...
12. ### Thermodynamics Energy transfer question

Homework Statement In a frictionless piston-cylinder system, there are 3 kg of R-134a initially at 280 kPa and 15 °C. Heat is transferred to the system in the amount 120 kJ. What will the final temperature of the refrigerant be (deg C)? Homework Equations Q - W = ΔU (internal energy) Q - Wb...
13. ### Possible error sources in thermal conductivity experiment?

Hello, my name is Stephen Lanford and I am currently working on a Physics II lab. I am solving for the thermal conductivity of four materials (glass, plexiglass, pine, and sheetrock) using data from thermal conductivity experiments. The experiments consist of a steam chamber at 100 C, a block...

Many textbook, particularly Forster Resonance Energy Transfer shows a diagram where transition of a donor nonradiatively excites an acceptor in the dipole interaction scheme. When considering spectral overlap, they explain the overlap of the phonon-sidebands of the two species. This seems to me...
15. ### Algodoo and Physics Analysis of Interactions

Homework Statement [/B] I have created a very simple Rube Goldberg device in Algodoo, and I need to analyze 3 correlating steps within it, using physics descriptives and equations. My primary focus is the ball as it hits the windmill, which I need to describe and calculate its velocity at that...
16. ### A Phonon-assisted energy transfer between lanthanides

Dear all, I am not understanding well the "phonon-assisted" energy transfer between lanthanide ions and I need some clarifications. There is a theoretical work by Miyakawa and Dexter (doi:10.1143/JPSJ.32.1577) which explains how phonon plays a role in transferring energy from one (4f-state of)...
17. S

### B Is Math the Key to Understanding Energy Transfer in Waves?

How can we show mathematically that a wave transfer energy?
18. ### Dimensional analysis: Energy Transfer

Homework Statement There is a paper in 1973: T. Kushida, "Energy Transfer and Cooperative Optical Transitions in Rare-Earth Doped Inorganic Materials I. Transition Probability Calculation", J. Phys. Soc. Jpn. 1973, 34, 1318-1326. DOI: http://dx.doi.org/10.1143/JPSJ.34.1318 that explains the...
19. ### A Question about energy transfer between Rare-Earth ions

Dear all, I have a question about one of the values presented in a paper, which is crucial in calculating energy transfer probability between two Yb3+ ions. This is the paper: T. Kushida, "Energy Transfer and Cooperative Optical Transitions in Rare-Earth Doped Inorganic Materials. I...
20. ### How do i calculate the energy lost by my catapult

I Have built a catapult for a 1st year engineering assignment, I know catapult are extremely energy inefficient and my theoretical catapult calculations prove that, but i don't know how to calculate the exact energy of my projectile as it hits the ground again, I can measure the projectiles real...
21. ### Where does heat energy go when dissipated in metal?

When heat is dissipated into a piece of metal(aluminum for example), what happens to the potential energy that was stored in the heat? Does it transform into another form of energy or is it absorbed by the atoms of the metal element?
22. ### I Energy transfer during uphill vs downhill running

Hello Physics Gurus, Please critique the following logic... When a runner hikes/runs to the top of a mountain, the chemical potential energy inside the muscles transferred into the potential energy of the runner's body mass at the higher elevation (Pe = mass*gravity*height = mgh). Energy is...
23. ### B Linear energy transfer for electrons

Hi! I have a question about Linear Energy Transfer for electrons. According to the definition the linear energy transfer is equal to the energy dE which a charged particle loses at a distance dl. But what does dl mean in case of electrons? Is LET calculated per unit of full path length or per...
24. ### Help with spring stiffness calculation (k)

Hi I was given the following problem in my coursework: Homework Statement "A spring is initially compressed by 50mm when a steel ball of mass 2kg is released from just being in contact with the uncompressed spring. Determine the spring stiffness (k) of the spring." Homework Equations F = mg...
25. ### Need Some Help Calculating Energy Transfer During Impact

Hi PhysicsForums, first post! So I was wondering how much energy would be absorbed by a shock absorbing material before it hit a vulnerable object. I've made a rudimentary sketch in paint to illustrate the situation. I've calculated the Kinetic energy of the incoming object (let's call it X)...
26. ### Energy transfer in elastic collision.

How do I derive the energy transfer equation in an elastic collision of two bodies of masses m and M respectively,using the energy and momentum conservation relations in the laboratory frame? $$\frac{1}{2} m_1 v_0^2 = \frac 1 2 m_1 v^2 + \frac 1 2 m_2 V^2$$ m_1 v \cos(\phi)=m_1 v_0 -m_2 V...
27. ### Physics Research in wireless energy transfer or Future space engines

Hi, i am a 2nd year B.E student in India,and a new user to this site(sorry for any mistakes :) ) .My question is i want to do research that primarily concerns these 2 areas viz.Wireless energy transfer, and future space engines(starwhisps,solar sails,etc),is there any way to achieve my dream,i...
28. ### Optimizing sound energy transfer through plastic medium

Hi everyone, I am looking to improve the transmission of sound from a small 1/2" electro-mechanical transducer through a plastic medium (about 1/4" thick). I understand plastic is not a great medium for this but I do not have the ability to change this. The defacto setup doesn't work too...
29. ### Energy Transfer and rate equation

What is the unit for energy transfer rate constant? I am confused because of the order of reaction of energy transfer. Consider the case for following energy transfer A* + C → A + C*. The star represent excited state. Then the rate equation for A* would be as follows: \frac{d[A^{*}]}{dt} =...
30. ### B Is energy transferred as a wave or particle in classical physics?

I read a line in the book "Quantum physics of atoms, molecules, solids, nuclei, and particles" by resnick The line is "in classical physics energy is either Transported by waves or by particles" I have doubt is it correct, like we say eneegy is stored in electric field, is electric field...
31. ### Energy transfer in particle collisions

Sometime ago, in my partial state of sleepiness and being awake (you could call it trance - yo!) I had a thought that during perfectly elastic collisions, it's the deformation of the colliding particles which transfer energy from one to the other. But doesn't that assume that there are empty...
32. ### What Is the Rate of Energy Transfer for a 0.050T EM Wave?

Homework Statement It is fairly easy to produce a static magnetic field of 0.050T in the lab. If an EM wave could be produced with maximum magnetic field, Bo = 0.050T a) what would be the rate of energy transfer (W/m2) ? b) what would the corresponding maximum electric field be? Note * Air...
33. ### B How does GR explain increase/decrease in speed?

OK, so my basic understanding is that GR is all about geometry of space-time. It's all geometry, no other mechanism. This explains why objects change direction due to gravity. But why does the speed increase? How does pure geometry cause a change in speed? Also, where does this kinetic...
34. ### Power: energy transfer per time, without mass displacement?

The classical definition of power is the rate of work per unit time, and the usual definition of work requires a mass to be displaced. However, power is alternatively stated as the rate of the transfer of energy. Now, suppose for example that one abstractly considers a light beam (without...
35. ### Space Shuttle, thermal energy transfer, book makes no sense

Homework Statement Space shuttle enters the atmosphere. (i) What happens to the transferred energy? (ii) how do the high temperatures generated in the shuttle enters the Earth atmosphere relate to the material used for the underside of the shuttle surface? Why is the underside not made from...
36. ### B What Is It Called When Energy Moves Between Objects Without Changing Form?

Q. When energy transfers from one form into another it is called ENERGY TRANSFER - eg, chemical to kinetic in a car, electrical to light in a lamp – but what is it called when energy leaves one object and enters another (eg, from a warm hand into a cold hand) but the energy doesn’t change from...
37. ### The Field Model of Energy Transfer in Actual Circuits

In this paper (http://science.uniserve.edu.au/school/curric/stage6/phys/stw2002/sefton.pdf) the author describes the transfer of energy in an electrical circuit as follows: "To explain energy transfer we need to look at what is happening outside the wires. As a consequence of the surface...
38. ### Energy Transfer in a Block Sliding Down a Ramp and Hitting a Spring

Homework Statement Homework Equations KE = 1/2mv^2 f = -kx U = 1/2kx^2 Kinematic equations F = ma The Attempt at a Solution Horizontal components of the block's weight: 8.38N Compression of the spring: f = -kx 8.37 = -500x x = 0.01674 m , which is wrong and I would be grateful if someone...
39. ### Energy transfer question (Use PE=KE or SUVAT ?)

Homework Statement Object falls from a tree which is 3m above the ground, what is its velocity when it hits the ground ? Homework Equations mgΔh=1/2mv2 or s=vt-1/2at2 The Attempt at a Solution Using the idea of PE=KE, as the masses cancel out I get an answer of V=7.66ms-1 However I thought...
40. ### Energy transfer from photon to an electron

Please tell me,why can't a photon transfer it's energy completely to a free electron?
41. ### Show that the Energy Transfer is given by

Homework Statement A Photon has undergone Inverse Compton Scattering, a charged particle of rest mass m0 has relativistic energy E >> m0, collides head on with a photon of frequency v, where hv << m0. Assume the complete process takes place in one spatial dimension, say x. Using the...
42. ### How does heat transfer take place?

I'm having a problem with understanding how energy flows from one body to the other. So gases at high pressure travel towards low pressured areas. So there is a reason behind this. Since molecules of gases have the tendency to move away from each other, they travel towards low pressured areas...
43. ### Why is the smallest energy transfer in quantum measurement uncontrollable?

Dear Friends! Root cause of indeterminacy in quantum measurement process is that the smallest energy transfer happens via the emission or absorption of a single photon,an irreducible and uncontrollable process. I want to understand it more convincingly.
44. ### Energy transfer in Newton's cradle

Homework Statement Three balls of masses m1, m2 and m3 are suspended in a horizontal line by light wires and are almost touching. The mass m1 is given a horizontal velocity v so that it collides head-on with the mass m2. Find an expression for the final kinetic energy of m3? What value of m2...
45. ### Energy transfer acceleration due to large energy difference.

In a hypothetical example i have been thinking about a hot substance such as tea is sitting on the bench the air around the tea is colder than the tea so the process of thermal equilibrium is underway. If the tea is much hotter than an ordinary example does this increased difference in heat...
46. ### Specific heat capacity - heat energy transfer

Homework Statement Find the mass of water that vaporizes when 3.39 kg of mercury at 243 °C is added to 0.476 kg of water at 90.0 ° Homework Equations q=mcT, q=mL The Attempt at a Solution When vaporising T=100degC. Heat lost by mercury = heat gained by water. 3.39kg x 139J/kg/C x...
47. ### Unclear formula for radiative energy transfer

Right, so I was going over the formula sheet for my upcoming exam in thermodynamics, and I've stumbled upon this formula: q=\frac{\sigma(T^{4}_{2}-T^{4}_{1})}{\frac{1}{\epsilon_1}+\frac{1}{\epsilon_2}-1} with a description that (I think) translates as heat flux density. I'm currently...
48. ### Can you help me understand how a deer transfers energy to different objects?

I need ideas on what how a deer transfers energy to atleast 5 objects. It has to be unique, or only 2-3 types of animals eating each other. I ran out of ideas when I got to deer. I also need to know what type of transfer it is.
49. ### Neutrinos change flavor, energy transfer

I have a similar question. Since the neutrino's has a rest mass I can observe it in a SR frame where it is at rest. Now if I measure the mass (say by energy absorption inside a light trap) at one time. To the degree necessary to distinguish it's state from the other neutrino states I get a...
50. ### Wireless Energy Transfer: Just Science Fiction?

There's been some buzz about wireless energy transfer for quite some time now, but it seems really far fetched to me that we will get any significant power usage out of wireless energy transfer. What do you guys think? Does this form of energy have any significant potential at all, or is it just...