Question

Large green plants are called ‘green mufflers’. Why?

Answer 1

Hint: Green plants help in maintaining the proper balance of nature. Planting of trees is thus a crucial step towards curbing atmospheric pollution.

Complete Answer:
Trees act as noise barriers to reduce noise pollution through a phenomenon called sound attenuation, i.e., the damping of sound. In general, noise attenuation occurs when sound waves dissipate over longer distances until there is no energy left to vibrate in the air. Trees attenuate noise by absorbing, deflecting, refracting and masking.
Sound absorption by plants: The stems, leaves, branches, and wood of a tree absorb sound waves. Thick, rough bark and fleshy leaves are the most effective at sound absorption due to their dynamic surface area.
Sound deflection by plants: When sound waves hit massive tree trunks, they do not vibrate because of their rigidity. Sound waves are reflected off the trunks and back towards the source. Whereas when sound waves hit flexible surfaces like leaves, it will vibrate and get transformed into other forms of energy. It can also change the phase of sound waves, which causes interference and eventually reduces noise.
Sound refraction by plants: Ground covering plants, vines on the walls and green walls help in achieving refraction of sound waves.
Sound masking by plants: Trees mask annoying noise when their branches sway, leaves rustle or stems creak. Birds and squirrels on the trees help in masking noise pollution with their chirping and squeaking.
Green plants are called ‘green muffler’s’ due to their assistance in the aforementioned ways in reducing noise pollution.

Note:
Broadleaved trees are more effective in blocking noise than needle-leaf trees. A good noise barrier is a mix of trees, shrubs and ground cover plantings. Noise pollution can interfere directly or indirectly with plants and can hasten the extinction of some species in another century which makes the green mufflers even more significant.