An Eccentric Anomaly: Physics

Ed Davies's Blog


Pages tagged: Physics

General physical things and other non stamp collecting

Primary vs Final Energy

Here's a correction to my previous Is PV Enough? post.

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Is PV Enough?

Specifically, could photovoltaic panels alone provide all the energy needs of the human race.

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Water Vapour and Relative Humidity

It's often said that 100% relative humidity (RH) corresponds to the amount of water vapour that the air can hold at the relevant temperature. I think some people have an image of the air being like a sponge and when all the little holes become full and the air becomes saturated the rest drips out. This is wrong and, in some cases, seriously misleading but just close enough to right in common cases that the myth keeps getting repeated. Part of the problem is that the easiest way to phrase discussions reinforces the idea.

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How big are newtons and joules?

Previously I've said that a newton is about the weight of a smallish apple and a joule is the potential energy of an apple on a table. A tweet by @UnitFact reminded me to check.

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Do radiators radiate?

Specifically, do the sort of metal devices that Europeans tend to screw to their walls and run hot water through in order to heat their houses radiate much heat, as opposed to transferring it to the room by convection and conduction? Similarly, what proportion of the heat emitted by underfloor heating is in the form of thermal radiation?

Of course they radiate some heat. However, it's commonly said that they work mostly by convection and conduction. I think that's right and it's quite reasonable to call them convectors for this reason. Unfortunately, some people get a bit carried away with this and say that radiation is completely negligible. I don't think that's quite so right.

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Infrared Myths

I see a lot of confusion about infrared when it comes to interactions with buildings, astronomy and so on. Here's a bit of a brain dump to refer to in such cases which I hope will throw some light, of various wavelengths, on the matter.

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A Rant About Kilograms On Mars

The CACM have published a reasonably interesting article by Gerard J. Holzmann about verification of the software on the Curiosity Rover: Mars Code.

Near the beginning, though, it says:

On Earth, Curiosity weighed 900 kg. It weighs no more than 337.5 kg on Mars because Mars is smaller than Earth.

Nope!

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Dehumidifier Arithmetic

The Navitron forum is having a discussion on dehumidifiers in which a few opinions are given and some numbers are produced but no arithmetic is used to connect these. Here goes…

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Resistance is Stainless

A couple of weeks ago Paul at the End Of The Road was wiring up some little bus bars using aluminium and M5 stainless bolts. I commented:

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