Answer to Question 1
The terrestrial planets Mercury, Venus, Earth, and Mars are all small and are composed of rock and metallic elements that condensed at the high temperatures of the inner solar nebula.
Answer to Question 2
The two major types of seismic waves are body waves and surface waves. Body waves travel through the solid body of Earth and are somewhat like sound waves. Surface waves travel along the ground surface or slightly under it and are analogous to undulations or waves on water surfaces.
An earthquake generates two types of body waves: P-waves and S-waves. P-waves, or primary waves are the fastest seismic waves and can travel through solids, liquids, and gases. S-waves, or secondary waves, are somewhat slower than P-waves and can travel only through solids. The velocities of P- and S-waves are determined by the density and elasticity of the materials through which they travel.
Surface waves travel along the surface of the ground, or just below it, and are slower than body waves. Surface waves generally produce a rolling or swaying motion. The two most important surface waves are Rayleigh waves and Love waves. Rayleigh waves (R-waves) are generally the slower of the two and behave like water waves. The motion of a Love wave (L-wave) is similar to that of an S-wave in that the particles of the material move only back and forth in a horizontal plane perpendicular to the direction of wave travel.
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One Module of the Primary Visual Cortex
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Graphs of Primary Trigonometric Ratios