# Questions tagged [energy]

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### What is the maximum distance for eavesdropping? [closed]

There is a closed question https://physics.stackexchange.com/questions/276667/what-is-the-maximum-distance-for-eavesdropping-sound-waves on Physics Stack Exchange and I thought this might fit better ...
5k views

### Why does "potential energy" have the word "potential" in it?

Imagine a block of mass $m$ placed on the ground. I slowly lift it up to height $h$. The work done by me on the block is $mgh$. This amount of energy is now stored in the block when it is at height $h$...
34 views

### How do you estimate the energy of an impact?

I am trying to determine the energy of elastic stress waves generated in a solid by an impact. I have a time domain waveform from a piezoelectric transducer that was placed next to the impact site, as ...
51 views

### How to convert car power into energy (MJ) used per km?

I am currently attempting to do an energy audit regarding how much energy my car uses per kilometer. I am not sure whether my approach to this is right, and it feels like I have made too many ...
41 views

### Understanding "total primary energy supply"

I am trying to wrap my head around the diagram and explanation here but can not understand completely how it is computed. https://energyeducation.ca/encyclopedia/Total_primary_energy_supply For ...
58 views

### Converting between MMBTU and MWh

a quick question: I want to convert between MMBTU and MWh to get at emission factors from energy. I have the following information: I use the data given in 40 CFR 98 (see EPA source here) by the EPA ...
93 views

### Dehumidification calculations

I'm looking at options for DIY dehumidification and am hoping to get a sanity check on some calculations, and verification that I'm using the right factors in the right way. As a reference point, I ...
86 views

### If the developing countries consumed as much energy per capita as China how much the current energy need would grow?

I recently saw this question and I immediately thought that the discussion was too limited to current energy production, it simply assumes that the amount of energy we use today is the amount of ...
140 views

### How do 3 blade turbines come so close to the Betz Limit?

I have seen many diagrams (see attached) that indicate that modern 3 blade turbines are nearly 50% efficient, which is about 80% of the Betz limit. Betz calculated his limit based on a theoretical ...
29 views

I am working on Lagrangian derived high-dimensional motion equations for a robot in matrix form. The structure of such an equation is known: $M(q)\ddot{q}+C(q,\dot{q})\dot{q}+G(q)=0$ In here, $M(q)$, $... 2answers 64 views ### What are some technical problems with generating electricity using a gas turbine or combustible engine at a gas flaring site? Numerous oil and gas exploration sites practice flaring for safety and disposal of unwanted low calorific gases. However, instead of just standalone burning the gas, why can't a gas turbine or ... 1answer 243 views ### What does MM prefix mean in MMtoe? I was reading documents about energy importation and came across the following: The import was of 5,915.87 MMtoe I wonder if MMtoe =$10^6*10^6$toe =$10^{12}$toe. First time coming across a ... 1answer 97 views ### Why do monocrystalline solar cells have rounded/cropped edges? What is the meaning of this croped part? Why do they crop it, rather than let it be full square? 0answers 48 views ### Why do solar cells need to be square-shaped? There were circular solar cells 30 years ago. Why do we have square-shaped solar cells now? Why square? Furthermore, Why do monocrystalline solar cells have rounded/cropped edges? 0answers 50 views ### Why does a system with zero resultant moment turn after temporarily force-tilted? Say a beam, 3m long from end to end, has a pivot placed at its centre of mass, at half its length i.e. 1.5m. Objects with weight 200N each are placed on both ends of the beam. The system is in ... 0answers 21 views ### Why doesn't the Stress Power in the theorem of the expended mechanical power contribute to the kinetic energy? The following is the formula of the expended mechanical power:$P(t)=\frac{d}{dt}\int \frac{1}{2} \rho\ v^2 dV+\int \sigma \colon d\ dV$where$P(t)$is the mechanical power entering ... 1answer 35 views ### Half-life Unit Notations I was looking for some element's half-life, on the following website: http://nucleardata.nuclear.lu.se/toi/listnuc.asp?sql=&A1=214&A2=214&Z=88 For 214,88-Ra, the half-life is shown to be: ... 2answers 45 views ### How to determine energy dissipated from work applied on a load cell I am using a load cell to see how much force people can apply on it, to help determine their health. I am integrating the force applied on the bracket in Newtons in relationship to time, giving me the ... 1answer 27 views ### Weibull distribution Units - ENGIEQSOL I am using Engineering Equation Solver, and it has been telling me the units of my distribution are inconsistent. According to a the book I am reading, I think it should be unitless (as it is a ... 2answers 70 views ### Bernoulli equation on moving cart Let’s say I have moving cart with velocity U . And water from pipe flows at velocity V with respect to ground The question asks to use Bernoulli equation , pressure is atmospheric in the top If I use ... 1answer 50 views ### Why am I getting wrong value here? A man threw a ball with force 10 N to two displacement of 5 m and 10 m. F = ma, so let mass be 2 kg. a = 5 m/s2. Work done = 10 × 5 and 10 × 10 = 50 Nm and 100 Nm. Now, since a = 5, I assumed that ... 1answer 46 views ### Can we say kinetic energy is tangential K.E? I saw this in my textbook that$\dfrac{\text{d}K}{\text{d}t} = \dfrac{\text{d}(1/2mv^2)}{\text{d}t}= F_t v$where$F_t$is the resultant tangential force on the body. Now, let$F_t= F\cos\theta$$$\... 1answer 37 views ### What does the author mean? Turbomachinery - Reaction I am reading a book of Fundamental Energy Systems. The author describes the rate of change in head for a turbomachine as:$$ \frac{1}{2}[(V_1^2-V_2^2)+(U_1^2-U_2^2)+(V_{R2}^2-V_{R1}^2)] = H =U_1V_{u1} ... 1answer 28 views ### Statistics on energy mix in Europe [closed] Does anybody know where to find statistics on the energy mix in Europe (preferred by country)? I can only find the share of renewables. I'd like to see the whole mix with a split into energy sources (... 2answers 43 views ### Hydraulic energy recovery for high-pressure, low flow (non-steady state) conditions What would be the best way to implement hydraulic energy recovery while de-pressurizing a pressurized volume of silicone oil initially at 1500 bar. Can a piston pump be concievably repurposed as a ... 1answer 55 views ### Is oil collapsing [closed] Oil industry in permain basin is collapsing. Also, no new technology or anything to save it this time. Is this the beginning of the end for oil? 4answers 4k views ### How does turning off electric appliances save energy We all know if we use less electricity we save energy. But the energy we're getting is result of burning (not necessarily the literal meaning) the fuel. Even if we don't use that energy that fuel is ... 0answers 31 views ### How energy intensive is creating artificial islands in the IJsselmeer? The City of Amsterdam is building a series of artificial islands for new housing. One of them is Centrumeiland. Its size is 13 ha. (130,000 m2). Its creation requires 800,000 m3 of sand (Source), i.e. ... 2answers 73 views ### Why do some metals with bcc structure show ductile-brittle transition in charpy impact test? I was learning about the charpy impact test and came across the graph on this webiste that shows the impact energy for bcc and fcc structures as a function of temperature. I tried searching for an ... 2answers 149 views ### How high will a flywheel catapult launch a payload? First off, this is not a homework question or anything like that. I'm trying to build a catapult to launch a payload using a flywheel as an energy device! It goes like this: The flywheel spins up to ... 0answers 28 views ### Determine Heating costs in$/kWh for a specific location

Suppose I wanted to find the average heating price for a specific location in the US, where: heating_price: The price of equivalent unit energy intensity of heating energy source (e.g. natural gas), ...
112 views

### Capacity credit vs capacity factor

What is the difference between capacity factor and capacity credit? I know that capacity factor = annual generation / (installed capacity * 8760) but I don't understand how capacity credit is ...
53 views

### Fluid Mechanics Question

I am preparing for GATE(Chemical). I need the answer of this question part 2 (question 54) as I am not able to find the mistake in my logic. I have applied the logic here as: Initial energy stored in ...
81 views

### How much time to melt marshmallow under heat lamp?

Using the Specific Heat Formula, I found that I need to apply 612J of heat to melt 18g of marshmallow. Marshmallow has a specific heat of 2 J/(g*C), melting point of 98.6°F, and a starting room ...
32 views

### Why Do Airborne Wind Energy Systems Use Kites And Not Balloons?

Title says it all, Why are AWE-companies like Makani spending years and millions of dollars developing drones, rather than simply using a balloon-based design? Wouldn't it be easier and faster to get ...
61 views

### Kinetic energy of a rigid body

A homogeneous disk with radius $R$ and mass $m$ rolls without sliding on a horizontal fixed plane. Peripheral point $A$ has velocity $v$. Determine the kinetic force of the disk. In my textbook they ...
32 views

### Clothoid Curve / Euler Spiral Energy Transfer

I've seen in an advertisement that Clothoid curves–also known as Euler Spirals–"transfer maximum energy" to a ball bearing that is rolled down it. Firstly, I was wondering if that might be ...
59 views

### calculating energy usage with measuring the temperature

I am an electrical engineer working on a project. My goal of this project is to make an IoT solution where I continuously measure the temperature of room in a building. I want to calculate the amount ...
32 views

### Why is the functional of an elastic system equal to it's total potential energy and why is it stationary at it's minimum?

Okay this was even quite difficult to formulate but let's start with some statement's in my FEM book: Elastic continuum has a functional which is equal to it's total potential energy Elastic system ...
64 views

### Understanding the total energy in a AA battery

AA batteries have about 4 watt-hours (14400 joules, 10620.9 pound-feet). Ignoring losses, does that mean a AA battery could theoretically lift 10,620.9 pounds, 1 foot high? You'd need an electric ...
24 views

### How do I correctly model this system of torsion springs?

I am currently designing a symmetric parallel mechanism that can be modeled as follows: Here, $\tau^j$ denotes actuator moments and $k_i$ are torsion springs constants. For a specific point in the ...
48 views

### What are the key technical challenges to development of traveling wave reactors?

I recently learned about traveling wave reactors (TWRs) on the Netflix Bill Gates special, as an example of a cutting-edge technology Gates is funding which has the potential solve several ...
715 views

### Calculation of the stored energy for a heat storage tank

There is a heat storage tank that is directly loaded from the top and the heat is also taken from the top. The colder water from the heating circuit return flow enters the heat storage tank at the ...
33 views

### Question about flow temperature and storage temperature in a cogeneration plant

Let's assume I have a cogeneration plant that produces heat with a nominal output. The heat is given into a heat storage tank, which is filled from above. The maximum flow temperature of the ...
132 views

### Calculation of the specific CO2 emission of a cogeneration plant for the produced electricity

Suppose I have a cogeneration plant that runs on natural gas and produces heat and electricity. The heat effeicieny is $\eta_{th} = 0.4$ and the electricity efficiency is $\eta_{el} = 0.4$. The ...
33 views

### Uses of orifice in Water Jet Cutting?

I wonder whats the usage of orifice/orifice plate in Water Jet Cutting Machines. To increase pressure(due to a smaller diameter with respect to the entrance cross-sectional area) or to convert to ...
49 views

### How to estimate wind generation using power curve?

I am trying to verify windfarmer generation estimates manually. To do so I am trying to manually calculate the estimated energy production (kWh) of a wind turbine. The information I have available is ...
49 views

### Clutch role in a micro hydropower

I've recently visited an old (about 60 years old) micro hydroelectric standalone installation. Total electric power is about 3 kW A/C. A local told me between generator + fly-wheel and turbine there ...
If we have a closed cylinder filled with a gas and we heat it, by $1^{st}$ law we have: $\Delta q=\Delta U$ (?) since $\Delta V$ = 0. But $\Delta H= \Delta U+ V. \Delta P$. What does that difference ...