Bulk Density
Content
Bulk Density Bulk density refers to the mass per unit volume of a substance under the conditions that powdery or granular materials are packed. (With pores and voids) It is defined by:
In this formula: po’’ is the bulk density (kg/m3); m is the mass under dry conditions (kg); Vo’ is the volume under packing conditions/ natural state (m3) . Bulk density (pb) is the mass of a unit volume of material in its natural state (with pores and voids) calculated as pb = M V Solid density is the mass of a unit volume of material without pores and voids. POROSITY OF A MATERIAL Porosity is a term which is used to describe an important physical property of most materials. It is the degree to which volume of the material of the material is interspersed (combined) with pores. Porosity is expressed as the ratio of the volume of pores present in a material to the bulk volume of the material expressed as a percentage. Mathematically expressed as: Porosity (%) = Volume of pores (empty space or void spaces) in a specimen X 100 Bulk volume (total volume) of specimen Solution Bulk/total volume of specimen Final level of water in the cylinder Original level of water in the cylinder Solid volume of specimen= (120 – 50) = 80ml = 120ml = 50ml = 70ml
Since, volume of pores = BULK VOLUME – SOLID VOLUME Then, volume of pores = (80 – 70)ml = 10ml
Therefore: Porosity (%) = Volume of pores (empty space or void spaces) in a specimen X 100 Bulk volume (total volume) of specimen = 10ml/80ml = 12.5% The rate of absorption of water will then depends on: a) The number of pores b) The extent to which the pores are connected The more the open and connected tiny pores are, the stronger the water absorption is; it is not easy for water to be absorbed if the pores are closed; if they are large and open, water is easy to be absorbed but is hard to be hold, and thus the water absorption is weak. Hence, for pores existing as isolated cavities absorption of water is less, since water cannot pass through the cavity walls. However, for cavities connected by fine capillary channels, water penetration is deeper into the materials. Example of materials which absorb fairly large amount of water is brick
Q2 A fluid is a substance that flows easily. Fluid pressure is the pressure at some point within a fluid, such as water or air. With the aid of a sketch, explain the process known as SIPHONAGE A siphon is a device designed to permit water to travel from a higher to a lower level, over an obstacle in between. It consists of an inverted U- tube. The bend of the tube connecting the two reservoirs must be filled with water. The atmospheric pressure (A) acts equally on the free space of the liquid in both reservoirs. The pressure at X at the top of the shorter limb, however, will be greater than that at Y , at the top of the longer limb, as a result of the difference in length of the water columns h and H.( the pressure at X is given by A-h , and the first of these is greater). Water will therefore move along the tube from X to Y, and so from the higher to the lower reservoir. This process is known as SIPHONAGE. Siphonage cannot take place until the bend of the tube is filled with liquid. 1. Once started, Siphonage will continue until air enters the shorter limb as a result of the water level in upper reservoir. 2. The levels of water in both reservoirs are the same as a result of Siphonage.
Q2d An experiment to show that pressure increases with depth. A demonstration of how water pressure increases with the depth of the water can be done with a large tin can. Punch nails holes in a vertical line up the side of the can every inch or several centimetres. Then fill the can with water. The water may just dribble out the top holes, but the increased pressure with depth causes the water to squirt out with more pressure at the bottom holes. This proves that at each point, pressure is acting horizontally and that the intensity of water increases with depth. Q3 Noise is usually defined as any perceived sound that is objectionable or damaging for a human. Noise is somewhat subjective, because one person’s ‘‘music’’ may be another person’s ‘‘noise but Sound is defined as a pressure disturbance that moves through a material at a speed which is dependent on the material. Sound is also said to be the sequence of waves of pressure that propagates through compressible media such as air or water. During propagation, these waves can be reflected, refracted, or attenuated by the medium. Acoustics is reproduction, phenomenon buildings and the science of the generation, propagation, transmission, reception, measurement and effects of sound and of the of hearing. It involves the study of sound levels both within in open air.
Noise is usually defined as any perceived sound that is offensive (unpleasant) or damaging for a human. Noise is somewhat subjective, because one person’s ‘‘music’’ may be another person’s ‘‘noise.’’ Noise can generally be defined as unwanted sound. Therefore what is sound? Sound is mechanical energy transmitted by pressure waves in a compressible medium such as air. OR Sound can also be defined as a pressure disturbance that moves through a material at a speed which is dependent on the material that describe the rate of oscillation(wavering) of sound waves, the distance between successive troughs or crests, the speed of propagation, and the pressure level or energy content of a given sound wave. Some sounds that could be classified as noise, such as the warning whistle on a train, are actually beneficial by warning people of potential dangerous situations. The unit of sound pressure in relation to the faintest sound detectable by a keen human ear is called a decibel (dB).
Noise Control in the Transmission Path Modifying the path through which the noise is propagated is often used when modification of the noise source is not possible, not practical, or not economically feasible. For noise sources located outdoors, one simple approach for noise control would be to move the sound source farther away from the receiver, i.e. make the noise path longer. For noise sources located outdoors or indoors, the transmission path may be modified by placing a wall or barrier between the source and receiver. Reduction of traffic noise from vehicles on freeways passing near residential areas and hospitals has been achieved by installation of acoustic barriers along the roadway. The use of a barrier will not be effective in noise reduction indoors when the sound transmitted directly from the source to receiver is much less significant than the sound transmitted indirectly to the receiver through reflections on the room surfaces. For this case, the noise may be reduced by applying acoustic absorbing materials on the walls of the room or by placing additional acoustic absorbing surfaces in the room. SOUND INTENSITY The energy transmitted per unit time and area by a sound wave OR Sound Intensity is the Acoustic or Sound Power (W) per unit area. The SI-units for Sound Intensity are W/m2. The difference in intensity of 10-8 watts/m2 and 10-4 watts/m2 (10,000 units) can be calculated in decibels as ΔLI = 10 log [(10-4 watts/m2) / (10-12 watts/m2) ] - 10 log[ ( 10-8 watts/m2) / ( 10-12 watts/m2)] = 40 dB Sound absorption describes the amount of reverberation within a room and its effect on sound quality and intelligibility (Intelligibility is a measure of how comprehendible speech is, or the degree to which speech can be understood.) Sound insulation describes the actual reduction in sound travelling from one area to another through a wall, floor or ceiling. Sound transmission in buildings results from both airborne and impact noise
In this formula: po’’ is the bulk density (kg/m3); m is the mass under dry conditions (kg); Vo’ is the volume under packing conditions/ natural state (m3) . Bulk density (pb) is the mass of a unit volume of material in its natural state (with pores and voids) calculated as pb = M V Solid density is the mass of a unit volume of material without pores and voids. POROSITY OF A MATERIAL Porosity is a term which is used to describe an important physical property of most materials. It is the degree to which volume of the material of the material is interspersed (combined) with pores. Porosity is expressed as the ratio of the volume of pores present in a material to the bulk volume of the material expressed as a percentage. Mathematically expressed as: Porosity (%) = Volume of pores (empty space or void spaces) in a specimen X 100 Bulk volume (total volume) of specimen Solution Bulk/total volume of specimen Final level of water in the cylinder Original level of water in the cylinder Solid volume of specimen= (120 – 50) = 80ml = 120ml = 50ml = 70ml
Since, volume of pores = BULK VOLUME – SOLID VOLUME Then, volume of pores = (80 – 70)ml = 10ml
Therefore: Porosity (%) = Volume of pores (empty space or void spaces) in a specimen X 100 Bulk volume (total volume) of specimen = 10ml/80ml = 12.5% The rate of absorption of water will then depends on: a) The number of pores b) The extent to which the pores are connected The more the open and connected tiny pores are, the stronger the water absorption is; it is not easy for water to be absorbed if the pores are closed; if they are large and open, water is easy to be absorbed but is hard to be hold, and thus the water absorption is weak. Hence, for pores existing as isolated cavities absorption of water is less, since water cannot pass through the cavity walls. However, for cavities connected by fine capillary channels, water penetration is deeper into the materials. Example of materials which absorb fairly large amount of water is brick
Q2 A fluid is a substance that flows easily. Fluid pressure is the pressure at some point within a fluid, such as water or air. With the aid of a sketch, explain the process known as SIPHONAGE A siphon is a device designed to permit water to travel from a higher to a lower level, over an obstacle in between. It consists of an inverted U- tube. The bend of the tube connecting the two reservoirs must be filled with water. The atmospheric pressure (A) acts equally on the free space of the liquid in both reservoirs. The pressure at X at the top of the shorter limb, however, will be greater than that at Y , at the top of the longer limb, as a result of the difference in length of the water columns h and H.( the pressure at X is given by A-h , and the first of these is greater). Water will therefore move along the tube from X to Y, and so from the higher to the lower reservoir. This process is known as SIPHONAGE. Siphonage cannot take place until the bend of the tube is filled with liquid. 1. Once started, Siphonage will continue until air enters the shorter limb as a result of the water level in upper reservoir. 2. The levels of water in both reservoirs are the same as a result of Siphonage.
Q2d An experiment to show that pressure increases with depth. A demonstration of how water pressure increases with the depth of the water can be done with a large tin can. Punch nails holes in a vertical line up the side of the can every inch or several centimetres. Then fill the can with water. The water may just dribble out the top holes, but the increased pressure with depth causes the water to squirt out with more pressure at the bottom holes. This proves that at each point, pressure is acting horizontally and that the intensity of water increases with depth. Q3 Noise is usually defined as any perceived sound that is objectionable or damaging for a human. Noise is somewhat subjective, because one person’s ‘‘music’’ may be another person’s ‘‘noise but Sound is defined as a pressure disturbance that moves through a material at a speed which is dependent on the material. Sound is also said to be the sequence of waves of pressure that propagates through compressible media such as air or water. During propagation, these waves can be reflected, refracted, or attenuated by the medium. Acoustics is reproduction, phenomenon buildings and the science of the generation, propagation, transmission, reception, measurement and effects of sound and of the of hearing. It involves the study of sound levels both within in open air.
Noise is usually defined as any perceived sound that is offensive (unpleasant) or damaging for a human. Noise is somewhat subjective, because one person’s ‘‘music’’ may be another person’s ‘‘noise.’’ Noise can generally be defined as unwanted sound. Therefore what is sound? Sound is mechanical energy transmitted by pressure waves in a compressible medium such as air. OR Sound can also be defined as a pressure disturbance that moves through a material at a speed which is dependent on the material that describe the rate of oscillation(wavering) of sound waves, the distance between successive troughs or crests, the speed of propagation, and the pressure level or energy content of a given sound wave. Some sounds that could be classified as noise, such as the warning whistle on a train, are actually beneficial by warning people of potential dangerous situations. The unit of sound pressure in relation to the faintest sound detectable by a keen human ear is called a decibel (dB).
Noise Control in the Transmission Path Modifying the path through which the noise is propagated is often used when modification of the noise source is not possible, not practical, or not economically feasible. For noise sources located outdoors, one simple approach for noise control would be to move the sound source farther away from the receiver, i.e. make the noise path longer. For noise sources located outdoors or indoors, the transmission path may be modified by placing a wall or barrier between the source and receiver. Reduction of traffic noise from vehicles on freeways passing near residential areas and hospitals has been achieved by installation of acoustic barriers along the roadway. The use of a barrier will not be effective in noise reduction indoors when the sound transmitted directly from the source to receiver is much less significant than the sound transmitted indirectly to the receiver through reflections on the room surfaces. For this case, the noise may be reduced by applying acoustic absorbing materials on the walls of the room or by placing additional acoustic absorbing surfaces in the room. SOUND INTENSITY The energy transmitted per unit time and area by a sound wave OR Sound Intensity is the Acoustic or Sound Power (W) per unit area. The SI-units for Sound Intensity are W/m2. The difference in intensity of 10-8 watts/m2 and 10-4 watts/m2 (10,000 units) can be calculated in decibels as ΔLI = 10 log [(10-4 watts/m2) / (10-12 watts/m2) ] - 10 log[ ( 10-8 watts/m2) / ( 10-12 watts/m2)] = 40 dB Sound absorption describes the amount of reverberation within a room and its effect on sound quality and intelligibility (Intelligibility is a measure of how comprehendible speech is, or the degree to which speech can be understood.) Sound insulation describes the actual reduction in sound travelling from one area to another through a wall, floor or ceiling. Sound transmission in buildings results from both airborne and impact noise
