# Why When Sawing Boards With A Circular Saw Usually

77. (Cl.) Indicate which of the following phenomena is inherent in both transverse and longitudinal waves: a) propagation in space periodic changes in physical quantities: elastic forces; acceleration, speed, displacement of particles of matter, bodies or parts thereof; b) the transfer of energy in space over time; c) lack of substance transfer; d) the emergence of an elastic force in the medium as a result of shear strain; e) existence in liquids and gases

78. (Cl.) List the general and various properties of transverse and longitudinal mechanical waves. (AnswersI. General properties: both types of waves a) are a periodic process, b) can exist in solids, c) are elastic, d) transfer energy, e) do not transfer matter. II. Various properties: f) in longitudinal waves, particle vibrations occur along the direction of wave propagation, and in transverse waves perpendicular to it; Unlike longitudinal, they cannot be excited in gaseous and liquid media.

§ 33. Wavelength. Wave velocity

79. (a, b-Cl, c-DZ.). the direction of the instantaneous velocity of one of the oscillating particles of the medium (see fig. 18, a; b; in) determine in which direction the wave moves in each of the three cases presented in the figures.

80. (a, b-Cl, c-D.Z.). In the direction of the wave velocity (see fig. 19, a; b; in) for each of the three cases, determine the direction of velocity of that of the oscillating particles, which is indicated by a point.

81 (D.Z.) Waves ran from the athlete who dived into the water. Determine their propagation speed if the wavelength is 0.5 m and the oscillation frequency is 4 Hz. (Hole 2 m / s)

82 (C) (idea: P.440 (437), ed., EMG) Tourists who camped on the shore of the lake, noticed in the distance a motor boat running parallel to their shore at a time when the boat was opposite them. After 60 s, the crest of the first wave reached the shore, and in the next 10 s, another 20 ridges located 1 m from each other. At what distance from the coast did the boat go?

§ 34. Sources of sound. Sound vibrations

83. (Cl.) What is the source of sound arising from sawing boards, logs and other materials?

84. (Cl.) Are the waves generated by the flapping of the wings of mosquitoes, flies, bumblebees and other insects longitudinal or transverse? Why do you think so?

85. (Cl.) Why do we hear the sound generated by the flapping wings of a flying bee or wasp, but not by the flapping wings of a pigeon or duck?

86. (Cl.) An ultrasonic signal emitted by a bat, propagating at a speed of 340 m / s, went the distance to the obstacle and back in 0.4 s. Determine the distance between the mouse and the obstacle, assuming that for the period of time between the radiation of the signal and the reception of the reflected signal, it did not change.

## Video: Why When Sawing Boards With A Circular Saw Usually

§ 35. Height [and timbre] sound. § 36. Sound volume

87. (Cl.) Why, when sawing a board with a circular saw, usually a much higher pitch sound occurs than when sawing the same board with a two-handed saw?

88. (Cl.) The farther we are from the sound source, the lower the volume of the sound it emits. Why?

§ 37. Propagation of sound. § 38. Sound waves. Sound speed

89. (Cl.) How does the energy of the oscillatory motion of the particles of the medium in which sound propagates change with distance from the sound source? What type of energy is it converted to?

90. (Cl.) On presented at figure 20 the graph shows how the coordinate of one of the points of the sounding string of the cello changes over time. Using the graph and knowing the speed of sound propagation in air, determine the length of the sound wave generated by the vibrations of this string.

91. (D.Z.) A female voice with a frequency range of 170-780 Hz is called contralto. What is the wavelength of the highest and lowest sounds that a contralto singer can play?

Examination No. 2 (based on the material of Chapter 2: §§ 24-26, 28-38)

º§ 39. Reflection of sound. Echo º§ 40. Sound resonance

92. (Cl.) The ultrasonic signal emitted by the echo sounder after reflection from the seabed was recorded after 0.9 s from the moment of its emission. At what speed did ultrasound propagate in water if the depth of the sea under the ship was 0.7 km?

93. (Cl.) It is known that any medium absorbs sound. Glass absorbs sound to a lesser extent than air. Nevertheless, the volume of sounds coming from the street with closed windows will be less than with open. Why?

Chapter III. Electromagnetic field

§ 42. Magnetic field and its graphic representation. § 43. Inhomogeneous and uniform magnetic field

94. (Cl.) On the figure 21 the magnetic lines of the strip magnet and the magnetic arrows 1, 2, and 3 are shown. Which arrow affects the magnetic field with the greatest force, and which with the least?

95. (Cl.) On the figure 22 Three lines of the magnetic field are shown. Is this field homogeneous or heterogeneous? At what point. A or B. will a greater force act on the magnetic needle from the side of the magnetic field? Justify the answers.

§44. The direction of the current and the direction of the lines of its magnetic field

96. (Cl.) A compass with an arrow established in the Earth’s magnetic field lies on a stage (see fig. 23). The horizontally located wires 1 and 2 are at the same distance from the arrow in the same vertical plane with it. In which direction. clockwise or counterclockwise. will the compass needle turn if we pass leftward currents through the wires and the current in the upper wire is greater than in the lower one? What will be the angle of rotation of the arrow: = 90º, > 90º, or

Thorium-234, half-life T = 24 days, the initial number of nuclei is N0