When the plane flies in the air, whether it can fly smoothly is closely related to the airflow. There are some irregularities such as local fluctuation and vortex in the airflow. This kind of irregular air movement phenomenon is called disturbed airflow in meteorology, also called turbulence and turbulence.
There are several reasons why the plane bumps in the strong airflow: crossing the area where the wind direction and speed of the high-altitude jet stream change rapidly, such as near the thunderstorm, and flying through the clouds. Low-altitude areas with unstable airflow due to uneven surface heating, windy areas caused by topography, turbulent areas caused by surface buildings, and wake areas that enter when following the plane in front.
The classification of masses is generally divided into mild, moderate and severe masses. 1-5 is a slight bump, so the crew doesn't need to take any measures, just inform the passengers to fasten their seat belts.
Never open the luggage rack when it is bumpy, lest the luggage hurt yourself. Don't sleep on the floor on intercontinental flights or night flights. Adult passengers should do a good job of monitoring children and baby passengers, and they should not wear seat belts because they are unwilling or crying. Pregnant women travelers can fasten their seat belts at the root of their thighs and put a soft thing in the middle, such as a small pillow.
In short, as long as you sit on the plane and fasten your seat belt, you can safely pass through the bumpy area and protect yourself.