复旦大学：《大学物理》课程教学资源（PPT课件，英文）Chapter 18 Wave Motion

Chapter 18 Wave motion

Chapter 18 Wave Motion

18-1 Mechanical waves eIn this chapter, we consider only mechanical waves such as sound waves. water waves and the waves transmitting in a guitars strings. Elastic mediums are needed for the travel of mechanical waves Mechanical waves can appear when an initial disturbance is made to the mediums On a microscopic level, the forces between atoms in the mediums are responsible for the propagation of the waves

18-1 Mechanical waves In this chapter, we consider only mechanical waves, such as sound waves, water waves, and the waves transmitting in a guitar’s strings. • Elastic mediums are needed for the travel of mechanical waves. • Mechanical waves can appear when an initial disturbance is made to the mediums. On a microscopic level, the forces between atoms in the mediums are responsible for the propagation of the waves

The particles of the medium do not experience any net displacement in the direction of the wave-as the wave passes, the particles simply move back and forth through small distance about their equilibrium position What is a wave? It is the process of propagating oscillation in space What are transmitted by a wave? Energy, momentum, phase., but the particles are not

•The particles of the medium do not experience any net displacement in the direction of the wave-as the wave passes, the particles simply move back and forth through small distance about their equilibrium position. What is a wave? It is the process of propagating oscillation in space. What are transmitted by a wave? Energy, momentum, phase…, but the particles are not

.18-2 Types of waves Waves can be classified according to their properties as following 1.According to direction of particle motion (a)" Transverse waves(横波)”: If the motion of the particle is perpendicular to the direction of propagation of the waves itself (b)“ Longitudinal wave(纵波)”: f the motion of the particle e is parallel to the direction of propagation of the waves See动画库\波动与光学夹\2-01波的产生23

18-2 Types of waves Waves can be classified according to their properties as following. 1.According to direction of particle motion (a)“Transverse waves(横波)”: If the motion of the particle is perpendicular to the direction of propagation of the waves itself. (b)“Longitudinal wave(纵波)”: If the motion of the particle is parallel to the direction of propagation of the waves. See动画库\波动与光学夹\2-01波的产生 2 3

2. According to number of dimensions 1-D Waves moving along the string or spring 2-D Surface waves or ripple on water 3-D Waves traveling radially outward from a small source, such as sound waves and light waves 3 According to periodicity pulse waves or periodic wave The simplest periodic wave is a"simple harmonic wave" in which each particle undergoes simple harmonic motion

2. According to number of dimensions 1-D Waves moving along the string or spring 2-D Surface waves or ripple on water 3-D Waves traveling radially outward from a small source, such as sound waves and light waves. 3 According to periodicity pulse waves or periodic wave. The simplest periodic wave is a “simple harmonic wave’’ in which each particle undergoes simple harmonic motion

The simplest periodic wave O Other kinds of periodic waves Square wave Triangle wave modulated wave Sawtoothed wave

y x o The simplest periodic wave Other kinds of periodic waves: Square wave Triangle wave modulated wave Sawtoothed wave

4. According to shape of wavefronts (a) The definitions of wave surface'(波面或同相面and wavefront(波前或波阵面? See动画库\波动与光学夹\2-02波的描述1 (b) The definition of a ray(s a line normal to the wavefronts, indicating the direction of motion of the waves Wavefronts are always l direction of Ray

4. According to shape of wavefronts (a) The definitions of ‘wave surface’ (波面或同相面)and ‘wavefront’(波前或波阵面)? See动画库\波动与光学夹\2-02波的描述 1 (b) The definition of ‘a ray’(波线): A line normal to the wavefronts, indicating the direction of motion of the waves. Wavefronts are always ⊥ direction of Ray

x Two different types of wavefronts Plane waves Spherical waves Plane wave: The wavefronts are planes, and the rays are parallel straight lines Spherical wave: The wavefronts are spherical and the rays are radial lines leaving the point source in all directions

Plane wave: The wavefronts are planes, and the rays are parallel straight lines. Spherical wave: The wavefronts are spherical, and the rays are radial lines leaving the point source in all directions. ★ Two different types of wavefronts: Plane waves Spherical waves

Ray(波线) Wave surface(波面) Wavefront(波前) 波前 波面 Spherical wave ray Plane wave

Ray(波线) Wave surface(波面) Wavefront(波前) *   Spherical wave Plane wave 波前 波面 ray

5. Waves in different fields in physics sound waves water waves earthquake waves light waves electromagnetic waves gravitational waves matter waves lattice waves

5. Waves in different fields in physics sound waves water waves earthquake waves light waves electromagnetic waves gravitational waves matter waves lattice waves