Posts Tagged ‘Energy’

Energy and Calories

The latter is an obsolete unit for energy anyway. The SI unit is Joules. 1 J = 1 N * 1 m = 1 kg * 1 m²/s² = etc etc – see that’s the whole idea of the SI system – you don’t have any coefficients.

Yet using Calories further makes it easier to construct misconceptions like the advertisement for Hydrive energy drinks: they give you lots of energy and are healthy because they have low Calories.


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“On the internet, everybody is an expert.” “Knowledge seems to correlate inversely with confidence.” And many other one-liners proven true in a godawful blogpost. Jennifer Marohasy has been a policy advisor for the Australian government, a prominent think tank member and an invited person to talk at many places. And here she attempts to refute the greenhouse effect altogether, and manages to violate conservation of energy at the same time (due to the confusion about energy versus power, see explanation below). It’s sad that people lacking basic high school level physics knowledge post something like this and others flock to defend it. It is just plain wrong. There is no opinion in these matters of physics, the model either describes nature well or it utterly fails.

If these are the people that set the policies in the western world, the decline has already started. I wonder if the internet has actually sped up this, or will it help prevent it? Are the experts always outnumbered by the lay people? Or would most people have the education (or logic capability and the time to quickly learn) to understand that what is peddled here is completely wrong?

Ultimately, when you get deeper into any complex issue, be it science or diplomacy, it becomes impossible for the average person to understand completely what is going on, and they have to trust others on what to do, how to expend the resources. But of course, the question becomes, who to trust. This is where peer review and open science should make it trustworthy. Spreading incorrect physics does not further public policy. You can’t get the right decisions out, if the data that goes in, is wrong.

The Greenhouse Effect Explained

In an equilibrium, an object receives an energy flow, and the energy also flows out at the same rate, otherwise it would be accumulating somewhere. This is the case with Earth. Energy is measured in Joules while power is Joules per second which also has the short hand Watts.

Now, Earth is in a vacuum so energy can flow in and flow out only via radiation. Also, objects that have more energy, that is, hotter objects, radiate more of their energy per second (the radiation power is dependent on the fourth power of temperature).

So, if the power going in is increased (like the sun getting brighter), then, initially, more energy is flowing in to Earth than flowing out, and Earth starts getting hotter (accumulating energy). The temperature increases and Earth starts radiating more and more, until it reaches an equilibrium where it radiates out as much as it gets in from the sun. Then the energy flows are in balance. So the result of cranking up the sun for Earth was an equilibrium state where there is more radiation in, more radiation out and more energy on Earth.

In the greenhouse effect, energy flows in normally but the energy flow coming out is limited slightly by some factor. Because the inflow is greater than the outflow, this starts accumulating energy on the object. Again the temperature (energy level) rises and the object radiates more and more, until it radiates exactly the amount that it is getting in from the sun. Then it is in equilibrium again and doesn’t heat up anymore.

There are lots of possible analogies. Water level can be thought of as energy, and water flow as energy flow or power. Then, a bucket with lots of holes can reach an equilibrium, where the amount poured in per second is the same that comes out of the holes. You can increase the water level either by increasing the rate you pour in (crank up the sun), or blocking some of the holes (the greenhouse effect).

Also, a clear night is usually much colder than a cloudy one. That is because when the sky is clear, the warm Earth can radiate it’s energy straight into space, while when there are clouds, the warmth stays in.

Designing spacecrafts, the concepts of power, energy, heat and radiation are very important too. In the vacuum of space, computer processors produce some heat that is hard to carry away (on Earth the heat is put into ambient air which is carried away by cooling fans, but there’s no air in space). They heat and heat until they simply radiate the heat away. But if there are some spacecraft walls, they might reflect the heat back. Hence there are radiators onboard spacecraft, where you pump coolant fluid from warm stuff inside to the outside where the heat radiates into space. If you have a nuclear reactor in space, the power system requires a temperature difference. The reactor is hot and the radiator is cool. If the flow to the radiator is cut, the reactor gets hotter (there is nowhere for the energy flow to go) and hotter until it melts and breaks. Then it probably goes subcritical, and the energy flow is cut. The heat radiates from the glowing droplets that are left behind.

And of course the last analogy is sleeping with a blanket. Your body produces some heat and that heat’s flow out is hindered by the blanket, hence you stay warmer. The blanket does not produce any energy and actually the blanket stays colder than your body at all times. Also, you can’t heat up a cold passive object by just wrapping it in blanket. The power (energy rate) produced by the body is constant and hence in an equilibrium the power flow out must be the same. A blanket lets through more energy when the temperature difference is larger. Hence your body temperature (energy level) grows until the heat flowing out is the same as what your body produces. You can get too hot easily with a thick blanket.

So, on Earth, how is it possible to only limit outgoing energy but not limit the incoming at the same time? This is because the energy comes in from the sun as mostly visible light, but the warm earth radiates in infrared. The greenhouse gases block only infrared light, hence blocking outflow but not intflow.

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