Science Buddies: "Ask an Expert"

we had an air tight container (with a thermometer inside) covered with white t-shirt. We exposed it to a heat lamp for 30 minutes. Recorded the data before and after. Repeated the exercise with black t-shirt. Recorded the data. We repeated the test several times and it was always warmer inside when we used the white t-shirt. ????
We decided to cover the plastic jar with foil so it should not let any light and run the test again this time it was warmer when we used the the black t-shirt.
Why it is not the same always?

Very interesting experimental observation and great idea to test again with the foil.

I believe what is happening is the white tee shirt alone is allowing light to pass through the shirt and heat up the container. The black tee shirt is absorbing more of the energy from the light and it is not passing through the shirt to heat up the container. Adding foil is eliminating the light passing through the shirt and therefore the containers are now only heated by the energy absorbed by each of the shirts. Using foil was a great choice, metals are excellent heat conductors.

Audrey

Thanks Audrey! what I find interesting is that I always insists on my son wearing light colors in summer when playing baseball but with this experiment I am not that sure it makes any difference. Would you agree with that?

Hi duquerre,

This question actually gets a bit more complicated than it might seem at first! There are three things that matter here:

- How much light is absorbed by a material. This will cause the material itself to heat up (and then, as it gets hot, transfer that heat to whatever it is touching - your son or the jar).
- How much light is reflected by a material. This light will bounce away without heating anything up.
- How much light is transmitted through a material. This light will heat up whatever is behind the material (your son or the jar).

As audreyln stated, in this case it looks like (before you put the foil on) the white t-shirt was actually letting enough light through to heat up the inside of the jar, even though it reflects more light than the black shirt.

This leads up to my question - did you use the exact same type of t-shirt (brand, material etc), one black and one white, for your tests? Even a black t-shirt is not completely opaque (meaning, if you hold it up to a bright light, you will still see some light shining through). This is different from, say, walls in your house that are painted white or black, and completely block all light from going through. So, this is an additional variable to consider when doing the experiment - the "weight" of the fabric might matter. For example, a very thin black t-shirt might actually transmit more light than a thicker white shirt. There are other things that could also skew the results - for example, how tightly you wrapped the jar in the shirt each time. If the shirt was loose and there were air pockets in between it and the jar, that could act as insulation affecting the results.

It sounds like you already took the right route to figure out your experiment, but I hope this explanation helps clarify things a bit. Ultimately, in the case of your son playing baseball, I think you will be safe sticking with the conventional wisdom that light colors will keep him cooler. Just keep in mind that there are other variables at play, like the thickness of the fabric and how loose-fitting it is (to allow better airflow).

-Ben

Ben, Thanks so much for your explanation. This has been such an interesting yet frustrating experiment. I realized that we never considered the air pockets created by the loose fabric. I will buy the fabric so I can make sure the weight is the same.

No worries! Heat transfer is actually a pretty complicated topic. There are entire college-level engineering courses on it . For even more background info, there are three types of heat transfer:

- Conduction - when heat passes between two solid objects that are touching each other. You can feel this when you press your hand up against something warm or cold.
- Convection - when heat is transferred by moving air or water - you feel this in a cool breeze on a hot summer day.
- Radiant - this is heat transferred by light (or other types of electromagnetic radiation that we can't see, like infrared). You feel this when you lay outside on a sunny day, or hold your hands in the air near a red-hot electric stove.

The challenge is that at first glance, this project just appears to be about radiant heat transfer (light heating up a t-shirt). But, you have that t-shirt wrapped around a jar with a thermometer inside, so as we discussed in the earlier posts, there are other factors at play:

- How much light gets through to the inside of the jar, heating up the air inside and the thermometer directly.
- How much light gets absorbed by the shirt, heating it up - that heat will then conduct to the surface of the jar, and then heat the air inside.

Taking all that into account, here's a new thought - what if you take tiny pieces of fabric (of the same size and weight, but different colors) and JUST wrap them tightly around the thermometer? Eliminate the jar entirely. That might give you a better idea of how much the fabric itself is heating up, and eliminate the extra problems because there are fewer "layers" between the fabric and the thermometer.

duquerre wrote:we had an air tight container (with a thermometer inside) covered with white Private Label T-shirt Manufacturer. We exposed it to a heat lamp for 30 minutes. Recorded the data before and after. Repeated the exercise with black t-shirt. Recorded the data. We repeated the test several times and it was always warmer inside when we used the white t-shirt. ????
We decided to cover the plastic jar with foil so it should not let any light and run the test again this time it was warmer when we used the the black t-shirt.
Why it is not the same always?

First of all your experiment is very creative firstly you use white T-shirt then black T-shirt and at the last foil. I want reminding you black color absorb more heat as compare to other color so that's why it was warmer when you used the black t-shirt

duquerre wrote:we had an air tight container (with a thermometer inside) covered with white Private Label T-shirt Manufacturer . We exposed it to a heat lamp for 30 minutes. Recorded the data before and after. Repeated the exercise with black t-shirt. Recorded the data. We repeated the test several times and it was always warmer inside when we used the white t-shirt. ????
We decided to cover the plastic jar with foil so it should not let any light and run the test again this time it was warmer when we used the the black t-shirt.
Why it is not the same always?

thanks for sharing your views.Black color is a good absorber for heat.So,we have to keep in our mind that not to wear black color clothes in summer season.