# science help: Help me with physics? - Help.com

## Help me with physics?

I’m REVISING for a REALLY important exam in January, and I don’t understand anything.
And this is one of the non-resitable exams that counts towards 40% of my science GCSE.

What the hell is a U-Value (Something to do with insulation?) and if a flooring material had a low U-Value would it be better for homes, or would a higher U-Value be a better for floor heating?

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### Replies (10)

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U-value is a measure of how quickly a wall loses heat. It has unit of W per square metre per kelvin. The lower the U-value the slower the heat transfer; and less energy is needed to keep the building warm.

Help me with: Insignificance.

fractal.scatter wrote:
U-value is a measure of how quickly a wall loses heat. It has unit of W per square metre per kelvin. The lower the U-value the slower the heat transfer; and less energy is needed to keep the building warm.

Okay thankyou, so what about flooring? would you want it to have a slow heat transfer?

From: http://www.combustionresearch.com/Inf…
“U” Value is the coefficient of transmission, i.e., the transmission of heat through the materials, which compose the building’s “envelope,” or outer shell.

“U” Value has an inverse relationship to “R” Value. For example, a building with material with an “R” Value of R-11 converts to an “U” Value of 0.09 ( 1/R or 1/11 = 0.09).

If you are going to build heat strips into the floor you want it to transfer that heat into the room quickly. So the material you use as flooring material should have a high U-value and a low U-value under it so that the heat is pushed up into the room.

have you tried bbc bitesize? I suck at science and that just about pulled me through!

lizzybug7 wrote:
have you tried bbc bitesize? I suck at science and that just about pulled me through!

I’m on there now, but It’s talking about things I know we haven’t learnt yet! I’m ridiculously confused.

becky(: wrote:

lizzybug7 wrote:
have you tried bbc bitesize? I suck at science and that just about pulled me through!

I’m on there now, but It’s talking about things I know we haven’t learnt yet! I’m ridiculously confused.

:/ well hope it all goes ok, I found this too http://physicsnet.co.uk/gcse-physics/… if that’s any help, the whole thing is completely over my head lol!

Same here, haha!
Biology is much simpler. We did quick exam similar to what we will sit for the real exams, and I didn’t revise for biology and got an A*
I revised for Physics and got a C! :/

becky(: wrote:
Same here, haha!
Biology is much simpler. We did quick exam similar to what we will sit for the real exams, and I didn’t revise for biology and got an A*
I revised for Physics and got a C! :/

physics is very hard though I mean at AS level only three people at my college out of a class of thirty passed physics and even then they where D/E grades so I wouldn’t worry about it seems few people are brilliant at physics a C sounds pretty good to me!

Scroll down to ‘understanding U values’

source wrote:
U-value is a term used to describe the amount of heat loss that occurs through an element of construction such as a wall or window. The lower the U-value the less energy is lost and the better is its insulating characteristics: a wall with a U-value of 0.3 W/m².K is twice as well insulated as a wall with a U-value of 0.6 W/m².K.

U-values allow regulators to set values which are neither material nor system specific but can be achieved by different combinations.

U-values are also a first guide for a designer and architect in setting the thermal performance of the building envelope. Practice has taught us that modifying these dimensions at a later stage in the building process is difficult and costly. Therefore U-values for building components are important parameters in the design process.

There you have it. :) Lower U value = higher energy savings (less heat loss/slower transfer)

Another site to look at: http://theyellowhouse.org.uk/themes/i…
Scroll down to INSULATION: THE JARGON OF INSULATION and you will find

article wrote:
The world of insulation has its own arcane jargon that needs to be mastered when specifying the most efficient materials and fittings. There are three ratings used for estimating heat loss: the k rating, the R rating, and the u value. (More information on k, R, u values below: what they mean, how they are calculated, and how to use them to assess your house’s energy loss.)

However, even if you do not have a head for maths, you may still need to know what these ratings mean in practical terms. Any manufacturer of building products and external fixtures such as doors and windows should know the R or u of their products. If you are looking for the lowest heat loss, all you need to know is:

R value - the higher the better
u value - the lower the better

Armed with this information, you can make direct comparisons between different products and materials. For example, normal off the shelf double glazing with aluminium frames has a u-value of 3.5. The high perfomance double glazing we used has a u-value of 1.6, half the level of heat loss.

The difference in thermal performance between seemingly similar products can be dramatic, which is why it’s so important to keep an eye on the R and u values. Normal 75mm concrete blocks have an R of 0.07. Solar concrete blocks have an R of 1.36. A wall built of normal concrete blocks will therefore lose nearly 20 times as much heat as a wall built of solar blocks.

Any good builder should be able to calculate the R and u values for you and can advise you about the relative costs of different insulation options for achieving the lowest heat loss.

I hope this helps you. :) Best of luck with your studies.

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