Illusion

https://www.youtube.com/watch?v=V7C318DGB38

The whole video is about an illusion which is not so obvious but probably many people have faced it at least once in their life. It is very interesting that it is only caused by the sun and shadows also it shows how accustomed we are to surrounding world. It is so that in many paintings, pictures, and even religions dark is down and light is up, this is so important that International Space Station has lights mounted on one side to make it easier for the astronauts, likewise cartographers create maps as if the sun was above them which is impossible in the real world. It shows how easy it is to twist and confuse our brains.

Convex
This polygon is convex

Concave


Dent
After the crash his car had many dents

Rain

https://www.youtube.com/watch?v=3MqYE2UuN24

The question in topic is taken from everyday life. Getting completely soaked in the rain is the situation which everyone has gone through at least once in his life. During this unpleasant time we often ask ourselves if is it better to run or to walk. This problem is explained in the video and the answer to this is not that obvious as it may seem and I think that not many people got it correct at first. I very much like the scientific way how the problem was explained, also pictures and animations used in this video were clear and helped to understand what author wanted to show.

parallelepiped (3D parallelogram)
parallelogram has 2 pairs of parallel sides which has the same length

slant
The needle must be slanted to fit properly