16 Why does water appear white while going over a waterfall?

We all know that water is colorless, but why does it appear white while going over a waterfall? Water that is flowing in canals and rivers appears muddy, however, it turns white as the water gets aerated when falling from a greater height. The flow of water changes from a laminar flow to a turbulent flow. Turbulent flow is usually rapid and is a non-uniform flow.

Water falling from greater height moves at very high speeds and contains trapped air that creates bubbles with dissolved oxygen. The rapid water movement causes dissolved oxygen to evaporate releasing oxygen in its gaseous form. Thus, these aerated bubbles make the waterfall appear white when falling from greater heights. (source)

17 Why do airlines have ashtrays in the toilets when you can’t smoke?

Planes have a strict “No Smoking” policy in place, but why then do they have ashtrays in their toilets? Smoking in planes was banned in the 1980s, but seeing ashtrays in toilets raises a concern of safety. One might tend to think that the planes might be old as they still contain these ashtrays. However, this may not be a reason for concern as it is mandated by law to place them in airplanes.

Ashtrays are placed in planes to diminish the chances of a fire breaking out in the plane. Despite, smoking being legally banned, a few mischievous passengers tend to light up a cigarette in the plane’s toilets despite warning signs.

If these ashtrays were absent, there are chances of the butts being thrown into the dustbin possibly causing a fire. The airlines help ensure the safety of their passengers by providing them a safe place to discard their cigarette butts. (source)

18 Why can’t bots check “I am not a robot” checkboxes?

Google’s reCaptcha system prompts us to manually check the checkboxes to identify our human validity every time. Why are bots incapable of carrying out this simple task? Basically, Google’s reCaptcha system is a predictive model.

This model is trained by mouse movements made by both humans and bots. As a human, when you manually check the checkbox, your mouse movement is recorded against a set of sample recorded data. If these movements match, you are proved to be a human.

However, in the case of bots, they have to perform an Optical Character Recognition to read the prompt image.

The OCR process is tedious and the bots are capable of bypassing the validation check. But the mouse movements tend to identify them. Human-controlled mouse movements are usually jerky, whereas the movements made by bots are very smooth and precise.

This technique of comparing the live mouse movements against sample data ensures that bots are not granted access to the page. If it fails, the reCaptcha system generates a difficult captcha that requires more recognition of the context of some displayed scenes. (source)

19 Why is it so difficult to type or move your fingers quickly when your hands are very cold?

During cold weather, we all notice that our fingers tend to move slowly. Why does this occur? All physiological functions in the human body tend to be reduced at lower temperatures. Body parts like fingers and toes are located at the extremities and tend to be affected first when compared to other body parts.

The small blood vessels that are present in our fingers constrict when the temperature drops to preserve heat. Due to this constriction of blood vessels, the nerves in our fingers become less responsive, and the fingers turn numb.

Due to the cold, the chemical reactions needed for contacts take a hit as well. This feeling of numbness decreases finger agility making it difficult to type or do other activities. (1, 2)

20 Do donated organs age according to the donor´s age, or do they adapt to the age of the new body?

This is a really tricky question as there are no set age regulations that exist for organ donation. During the time of donation, the donor’s organs are evaluated to determine their suitability. It was presumed that the success rate depends on the health of the organs and not on the age of the donor.

However, a recent study suggests that the donor’s age during the graft is crucial and varies significantly for each organ. The human body tends to attack the transplanted organ thinking it to be a foreign body. The patient has to be put under immuno-suppressants to ensure that organ rejection does not take place.

In kidney transplantation, the age was considered to be within the third decade of the donor. For heart transplants, the negative effects are noted if the age of the donor is above 40 years. For liver transplants, it was determined to range between 30 and 50 years.

For lung transplants, the negative effect was noticed over the age of 50 years. Thus, the donated organs age according to the donor’s age rather than the receiver’s age. Furthermore, irrespective of the age of the donor, transplanted organs tend to be little weaker and proper care has to be taken to ensure its survival rate. (source)