Air sticky frisbee

1. Content:

There is a long cylindrical transparent device set up on the booth, which contains two parallel disks that are not connected. Participants press the start button, and the motor drives the upper disc to start rotating. Observe that the lower disc is still in a stationary state. This is because the distance between the lower disc and the upper disc is too far and there is not enough viscous force, so they did not rotate accordingly; When participants adjust the height of the central axis to reduce the distance between the two discs to a certain extent, observe that the frisbee below also begins to rotate with the disc above; This is because air has viscosity, and when two disks are close together, their motion states will affect each other.

2. Principle:

Air viscosity

Air is a typical viscous fluid, and only the ideal gas we learn in textbooks belongs to the category of fluid that ignores viscosity. This is the difference between ideal gas and actual air:

The viscosity of air changes with temperature. The lower the temperature, the lower the viscosity of air, and the higher the temperature, the greater the viscosity of air (this is the opposite of liquids, where the viscosity of liquids decreases with increasing temperature). When the temperature increases, the viscosity of the liquid decreases because the viscosity of the liquid is mainly caused by the cohesion between molecules. When the temperature increases, the cohesion weakens, resulting in a decrease in viscosity. The main reason for the viscosity of the gas is the thermal motion of the gas molecules. The higher the temperature, the stronger the thermal motion, resulting in a greater viscosity.

3. Purpose:

Exhibition items utilize simple mechanical interactive devices to enable participants to understand the stickiness of air.