لخّصلي

A guardian dog rests its ears on the ground to better hear sounds, as sound travels faster through solids. Sound is heard from all directions because it spreads outwards in spheres from its source. Violinists adjust string length to alter the frequency (pitch) of the sound. Musical notes have uniform frequencies, unlike noise, which is non-uniform, making sounds like drills and loudspeakers uncomfortable. Construction workers wear silicon earplugs for noise protection. A 251 Hz tuning fork sounds rougher (lower pitch) than a 512 Hz one. Sound intensity decreases proportionally to the square of the distance; hence, front row seating is preferable. Sound intensity also decreases with decreasing amplitude of the vibrating source (as seen with a vibrating ruler), and is directly proportional to the square of the amplitude. Resonance boxes increase sound intensity by enlarging the vibrating surface area. Lutes use hollow wooden boxes for the same reason. Sound travels with greater intensity in denser mediums, like carbon dioxide compared to air. Finally, pianos and violins can sound different even with identical intensity and pitch due to differing harmonic tones accompanying the fundamental tone.

Give reasons for:

1. 
   

   The guardian dog puts its ears on the ground when it sleeps at night. Because the sound velocity through solids (the ground) is larger than that through air

   
   


2. 
   

   Sound can be heard from all surrounding directions.

   
   

Because sound travels through air as spheres of compressions and rarefactions whose centre is the sound source.

3. 
   

   The violin player changes the length of strings during his play. To change the frequency of the produced tone.

   
   


4. 
   

   The difference in frequency between the tone (note) and noise.

   
   

Because musical note (tone) is of uniform frequency, while noise is of non-uniform frequency

5. 
   

   The sound of drill and loudspeaker is uncomfortable to be heard. Because it is sound of non-uniform frequency.

   
   


6. 
   

   Some construction workmen use ear plugs made of silicon.

   
   

To protect their ears from the noise.

7. The tuning fork of frequency 251 Hz gives rougher sound than that produced by another tuning fork of 512 Hz.

Because the sound of the tuning fork of frequency 251 Hz is low pitch, while that of frequency 512 Hz is high pitch.

8. • The intensity of sound decreases four times as the distance between the ear and sound source is doubled.

• It is preferred to sit in the first rows more than sit in the back rows in lecture classes. Because the intensity of sound is inversely proportional to the square of the distance

between the ear and the sound source.

9.• The intensity of sound decreases as the amplitude of the vibrating source decreases.

• The sound intensity which produced from a vibrating ruler will be decreased with time passes.

Because the sound intensity is directly proportional to the square of the amplitude of the vibrating source.

10. The intensity of sound increases when the sound source touches a resonance box.

Due to the increase of the vibrating surface area.

11. The strings of a musical lute are fixed on a hollow wooden box.

To increase the vibrating surface area which leads to an increase in sound intensity.

12. Sound travelling in air has less intensity than that travelling in carbon dioxide.

Because the density of carbon dioxide gas is more than that of air, since sound intensit is directly proportional to the density of the medium.

13. The piano sound differs from that of the violin even if they have the same intensit and pitch.

Due to the difference in harmonic tones that associate the fundamental tone of each of them.