Absorption

• (acoustics)

1. The property of a material that changes acoustic energy into (usually) heat energy. A material or surface that absorbs sound waves does not reflect them. Absorption of a given material is frequency dependent as well as being affected by the size, shape, location, and mounting method used. Source: Church Audio & Acoustics Glossary
2. In acoustics, the changing of sound energy to heat. Source: http://www.owenscorning.com/around/sound/glossary.asp
3. The opposite of reflection. Sound absorption results from the conversion of sound energy into another form, usually heat or motion, when passing through an acoustical medium. When a sound wave encounters resistance, absorption occurs. Absorption is measured in sabins (after Wallace Clement Sabine). One sabin is the amount of absorption offered by one square foot of open air. Glossary of Acoustic Terms
4. Absorption in the context of sound refers to the process of reducing the sound energy by converting it into heat energy. Sound absorbing materials such as foam, carpet, or fabric-covered panels are used to reduce echo and reverberation in a room or other enclosed space, which makes the sound clearer and more intelligible.
   
   Sound absorption is measured using a coefficient (alpha) which ranges from 0 (no absorption) to 1 (total absorption). The sound absorbing materials with high coefficient value such as open-cell foam or mineral wool are considered to be the most efficient at reducing sound energy.
   
   Absorption is the opposite of reflection. When sound waves hit a surface that is reflective, such as a hard wall, a significant portion of the sound energy is reflected back into the room, which can cause echoes and reverberation. Absorption helps to reduce the amount of sound energy that is reflected, which in turn improves the acoustics of the space.
   
   The absorption coefficient is frequency dependent and different materials have different properties at different frequencies. Some materials like foam, mineral wool, and some porous materials are more efficient in absorbing high frequency sounds, while others like heavy curtains, carpets, and upholstered furniture are more efficient in absorbing lower frequency sounds.
   
   In addition, the thickness and the coverage area of the material also affect the sound absorption. In general, thicker materials and larger coverage area provide more sound absorption.

• (biology) the taking up of substances or their passage through the walls of cells Source: Noland, George B. 1983. General Biology, 11th Edition. St. Louis, MO. C. V. Mosby
• (biotechnology) The process of absorbing; specifically:

1. In physiology, it refers to the movement of liquids and solutes into cells by way of diffusion or osmosis.
2. In chemistry, it refers to the drawing of a gas or liquid into the pores of a permeable solid.
3. In immunology, it refers to a process in which an antigen or antibody is used to pull an analogous antigen or antibody out of a solution.

• (environment) The uptake of water, other fluids, or dissolved chemicals by a cell or an organism (as tree roots absorb dissolved nutrients in soil.) Source: Terms of the Environment
• (geology)

1. The phenomenon observed when a pleochroic mineral is rotated in plane polarized light. In certain positions, the mineral is darker than in others, owing to the absorption of light.
2. In hydrology, a term applied to the entrance of surface water into the lithosphere by all methods. AGI
3. The reduction of light intensity in transmission through an absorbing substance or in reflection from a surface. In crystals, the absorption may vary with the wavelength and with the electric vector of the transmitted light with respect to crystallographic directions.
4. Any mechanism by which energy, e.g., electromagnetic or seismic, is converted into heat.
5. Taking up, assimilation, or incorporation, e.g., of liquids in solids or of gases in liquids. CF: adsorption
6. The entrance of surface water into the lithosphere by any method.
   Source: Dictionary of Mining, Mineral, and Related Terms

Compare adsorption.