why can we see dust particles in the air in bright light and what is keeping them up
We can see dust particles in the air in bright light for two main reasons: the scattering of light and our visual perception.
When light encounters small particles, such as dust, in the air, it scatters in all directions. This scattering process causes the light to disperse and reach our eyes from different directions. This scattering of light is called the Tyndall effect. Dust particles are usually larger than the wavelength of visible light, which is why they can scatter light effectively.
The second reason we can see dust particles is our visual perception. Our eyes are sensitive to changes in light intensity, and dust particles in the air can reflect or scatter light, creating tiny bright spots in our field of vision. Since these particles are floating in the air, they appear to be moving or floating themselves.
As for what keeps the dust particles up in the air, it is mainly due to their small size and the presence of air currents. Dust particles are usually very small, ranging from a few micrometers to several tens of micrometers in diameter. Because of their small size, they are subject to the random movements caused by the constantly circulating air currents. These air currents can be caused by natural factors such as convection currents or movement of people, or by mechanical factors such as fans or air conditioning systems.
The combination of the dust particles being light enough to be carried by air currents and the constant movement of air keeps the particles suspended in the air for extended periods of time. However, eventually, gravity will cause the dust particles to settle down on surfaces or be removed through various cleaning methods.