Physics anyone? LOL

well I've got this physics assignment with some questions on it
one of them is: write up an explanation that is understandable by a 9year old of why a cup water at 30degrees mixed with another cup of water at 30degrees doesn't make the temperature to 60degrees

having trouble explaining this in simple terms... help anyone?

the second questions asks, a metal rod is heated, this rod contains copper, platinum, iron and brass. these are just stuck next to each other. the order of the metals in the rod is
|copper | Platinum|
|Iron | Brass |

we have to determine the shape it would take after its heated and the metal expands
what I would like to know is how to determine this, my friends say that it has something to do with the specific heat capacity but I don't really get it. thinking of changing subjects soon ==

Brass = 0.377kJ/kg K
Copper = 0.39kJ/kg K
Iron = 0.46kJ/kg K
Platinum = 0.13kJ/kg K

not sure if thats right or not but... is having higher specific heat capacity supposed to mean the metal expands more?

 

To increase the temperature you need to apply heat to the water, for example by putting a flame under the cup. When you mix two cups of water there is no heat being used, if anything by pouring the water from one cup into another you might even reduce the temperature.

Good luck, nine year olds are smarter then you think, and will ask the hardest questions to answer.

 

Tell the child that increasing its volume does not essentially increase its temperature. The temperature is constant.

 

The only way to explain it to a 9 year old is to completely ignore the thermodynamics behind the event, and simplify it to this:

30/1 = 30
30/1 = 30
(30+30)/(1+1) = 60/2 = 30

A 9 year old should be able to understand division and fractions. Obviously these example equations are flawed, most simple of reason being that Celsius and Fahrenheit can not be used directly in energy equations because their 0 doesn't mean zero energy. The temperature needs to be converted to K first. It's been a while since I've done any thermodynamics stuff, but I'm pretty sure if the temperature is given in K (or converted to K) you can simply do what I mentioned to find the resulting temperature of the mixture.

 

Ya, in this case with merely averaging the "energy" per unit volume, it works in Celsius too, without any problems. Celsius cannot always be used in thermodynamics equations though, so usually it's easier just to add ~273 to the value before plugging away.

 

hmmm....
how come I never learnt anything about brackets in grade 4 D: lol
but yea.. thanks you 4 but what if they ask why to all that D: haha

 

ahh okay... i understood that ;D it should be fine haha thanks ;D
i posted another question that i didn't get, theres a third question but i got that haha
its about how people are able to walk over hot coal and hot get severely burnt lol

 

In order to get this strait Potential energy is really saying that all the elements have the power to create some source of heat or thermal expansion. The objects that are receiving the output energy are being generated at the same rate until it has similar kinetic energy.

A long with the metal to absorb heat capacity it depends on the alkali of the metal because each metal has its owns properties. The transfer rates would be entirely different to each one.As soon as the metal expands and then cools off it would then have conserved its energy. Am not entirely sure but I think it would retain its original shape.??

It would likely come down to the element though since those come in three things either a solid, gaseous, or a liquid. Heat capacity then would only depend on the materials mass:
C= J/ kg x K
Is generally the main equation for solving specific heats.

I think it would depend if the metal were tightly compressed or not. I do understand that if the substance were doubled then the heat capacity would then also be doubled.

As for the person walking on the coals, once they set foot on those both of them rub enough heat on each other that does not exceed their own.

Sited sources:
http://www.wordiq.com/definition/Thermal_energy
http://physics.about.com/od/thermodynamics/p/thermodynamics.htm
http://en.wikipedia.org/wiki/Thermal_energy
http://www.britannica.com/EBchecked/topic/591388/thermal-energy
http://en.wikipedia.org/wiki/Heat_capacity

 

Algodoo, that is all I need to know about physics...
http://www.algodoo.com/wiki/Home

 

But for me, the definition of a "9 year old's understanding" can vary.

 

Personally I think that for many 9 year olds there is no way to dumb this answer down so they understand it. I mean, you'll be able to tell them the answer, but I can guarantee that most of them would walk away without understanding why. In the US, nine years old is either 4th or 5th grade. You know the basic arithmetic functions, addition, subtraction, multiplication, division. You have not been formally introduced to order of operations, negative numbers, complex numbers, etc while in the 4th grade. 5th grade may start on some of the basics, 6th grade working on them, and finally by 7th grade you will begin Algebra. Even boiling it down to the most simple equations pushes the boundary of 9 year old understanding.

As a result, I also think that any physics instructor that asks you to dumb down thermodynamics to be understood by someone who has barely even started understanding the basics of the mathematics required for simple algebra needs to be slapped.

Physics and advanced mathematics go hand in hand. Trying to separate them is a pointless task.

 

Many students don't actually begin Algebra until high school anymore in the U.S. I didn't have it until I was in the 8th grade myself, and I was a year ahead math-wise of most other people. I feel like with a proper explanation, a 9 year old could understand the concept though.

 

LOL, I couldn't agree more, if only I could slap my teacher without any penalties haha

 

As far as your second question, I'm not certain if Specific Heat and Thermal Expansion are related (I do not believe they are) but the only thing important is the thermal expansion. The metal with the greater coefficient of thermal expansion will expand more, causing the metal to curve towards the side with the metal with a smaller coefficient. So either the metal is going to look like a C, a Backwards C, an S, or a Backwards S.

It is how many analog dial-style thermometers work, the dial is attached to a long coiled strip of two metals with different coefficients. As the temperature changes slightly, the coil tightens or relaxes, causing the dial to work. Where I work, we extrude aluminum at about 1000 degrees F, and about 250 feet long. As it cools to room temperature you can watch the metal actually move. It's pretty interesting just standing there next to the metal and it looks like someone is pulling the 200+ foot bar away from you, when really it's just the metal shrinking.

Coefficients of the Thermal Expansion are a property of the metal that you'd have to look up in a table. Usually given in terms of the amount they expand, per given length of the material, per degree of temperature change. Like Inches per Inch per Degree F. Aluminum has an expansion coefficient of 0.00001244 inches per inch per F. So for every inch of aluminum, the metal will grow (or shrink) 0.00001244 inches per 1F change in temperature. So as that 250 foot bar of aluminum at work goes from 970F to 70F, it shrinks by almost 33 inches. If it were attached side by side to a metal that only shrunk 20 inches, the piece of combined metal would curve towards the aluminum side.

 

oh umm
1 other quick question i forgot to mention
its for question 3, thermal conductivity
they give me this equation of

k= Rd/(T2-T1)A

i cant find this equation through google, I'm sure that its the equation of thermal conductivity but i do not know that the other variables stand for. Help anyone? lol

 

My guess:

k = kelvins
T1 and T2 = temperature 1 and temperature 2

The Rd and A though, I'm unsure of. Hell, I'm not even 100% on what I put above.