My favorite subject is science, because I have learned a lot of scientific principles and increased my scientific knowledge. I like this course very much.

At the beginning of school, the teachers distributed a book called Science. When I got home and opened the book, I was deeply attracted by the contents. The first lesson is the air around us. Through the teacher's detailed explanation in class, I understand that almost all living things on the earth need air. Clean air is the foundation of our health, and polluted air contains a lot of harmful substances, which will endanger human health and plant growth when it is seriously polluted. For example, automobile exhaust is a serious pollution. It can paralyze people's spirit, cause hypoxia in the body, damage the brain, lead to memory loss and even lead poisoning. Therefore, the World Health Organization stipulates that September 22nd every year is car-free day, calling on people to adopt green travel mode to protect our surrounding environment. Give people a green sky. On weekends, people like to go to the suburbs to play. They go there to breathe fresh air and enjoy the green world.

Air is a very important thing in our life. It can help people breathe and keep plants and animals alive. Air is a mixture of many gases. Oxygen accounts for about 2 1% of air. Others are mainly nitrogen, accounting for about 78% of the air, and a small amount of carbon dioxide and water vapor. Under the guidance of Mr. Zhu, we did an interesting experiment in class, which proved that air is made like this. In the air, it is divided into hot air and cold air.

A long time ago, people mastered the principle that hot air rises and cold air falls, thus invented the hot air balloon. During the Three Kingdoms period, we in China invented "Kongming Lantern" based on the rising principle of hot air, and applied it to the battlefield. 1783, the French made a manned hot air balloon by using the principle of hot air rising, so that people could enjoy the journey to their heart's content.