6. Why does a candle not produce smoke when burning, but lots of smoke when you blow it out?
There are two parts of a candle: the wax and the wick. The wick is the thread-like thing that sticks out and which we light with a match. The wax is the fuel that burns producing light through the capillary action of the wick. When the candle is burning, we do not see smoke coming out of it. When we blow it out, what we see is not smoke but vaporized paraffin wax that was acting as fuel. The candle wax is not just melting, it is also vaporizing.
The vaporized paraffin wax is to candle wax what steam is to water. When we blow out a candle, some heat due to combustion remains in the wick. This heat continues to vaporize the candle wax for a few seconds. As there is no flame, the wax doesn’t burn properly and condenses in the colder air around the wick forming the smoke which stops after a few seconds and turns solid. Try an experiment of blowing out a candle and re-lighting it through the smoke without touching the wick. It acts as a conclusive proof that the smoke is indeed vaporized candle wax. (source)
7. Why do men lose weight faster than women?
A study that was published in the journal Diabetes, Obesity and Metabolism talked about how 2,200 overweight adults from Europe, Australia, and New Zealand were put on an 800-calorie diet for eight weeks. At the end of the eight-week period, it was observed that men lost 16% more weight than women. A few other not-so-good results were observed in women including a decrease in HDL cholesterol, bone mineral density, and lean body mass, all of which can cause a slow metabolism.
The reason why men lose weight faster than women is because men are physiologically built to burn fat faster. They have a higher metabolic rate and more lean muscle mass that consumes more calories. Because men have a higher metabolic rate, they need to consume more calories. In the case of the study mentioned above, as both men and women consumed an equal amount of calories, a larger calorie deficit was created for men which resulted in the shedding of more kilograms. (source)
8. Why does our skin get darker and our hair gets lighter under the Sun?
Our hair and skin both have melanin, a pigmented polymer that serves as a protection from the ultra-violet (UV) rays of the Sun. Melanin is responsible for absorbing and scattering the UV rays, but in case of prolonged exposure, it degrades. Our skin cells react to the UV rays causing the body to produce a hormone that binds to melanin-making cells. This makes the skin produce more melanin which becomes darker as it disperses from the lower layer of the skin to its upper layer. This is what darkens our skin and causes a suntan.
In case of our hair, since the cells are dead, new melanin is not produced once the melanin that is already present is exhausted. The hair cells are comprised of structured proteins, lipids, water, and pigments which in no way help the hair retain its original color. So, the hair gets lighter under the Sun and remains that way until they are cut and new strands grow in the place of the damaged, lighter ones. (source)
9. Why don’t we recognize own voice in a recording?
It is common to not to “sound like yourself” in recordings, and there is a reason. When we hear other people talk, the sound waves travel through the air and vibrate our eardrums. The same happens when we hear our own voice in addition to one more thing. Our vocal cords vibrate when we speak, and these vibrations are a second source of sound for us. So, when we speak, what we hear is a combination of these two sounds.
When we hear a recording of our voice, the only thing we hear is the external stimulus and not the vocal cord vibrations making it sound very different to us, almost unrecognizable as we are not used to hearing it. According to a study, when people heard recordings of their own voices, only 38% were able to immediately identify their own voice. The recording of our own voice is at a higher pitch and does not have a false sense of bass like the one we have when we hear ourselves speak. (1, 2)
10. Why do our fingernails grow faster than our toenails?
Our fingernails grow two to three times faster than our toenails. There are a lot of similarities between our fingernails and toenails. Both have a distal matrix (below the cuticle) from where new nails grow. The distal matrix has epithelial cells which die over time and leave behind the protein keratin. A key enzyme called transglutaminase is mixed with keratin and other proteins and fats which then grows into a hardened nail. However, the growth patterns of the nails in the toes and the ones in the fingers are different.
One popular theory for the slower growth of toenails is that lesser blood blow reaches the feet than the hands resulting in lesser oxygen and nutrients for the growth of new cells in the toenails’ distal matrix. We also tend to cover our feet in socks and shoes reducing circulation. Another theory is that our fingernails undergo more trauma than our toenails as we use our hands more and for a variety of tasks. The trauma caused brings about an increase in the growth of the epithelial cells which results in more growth. It has also been observed that as we age, our nail growth slows down by around 30%. The growth also slows down in the winter. (source)