Answer to Question 1
Answer: An echo is reflected sound. Because sound from a small source spreads out via the inverse-square law, sound intensity per unit area decreases with distance to the reflecting surface, and when reflected continues to decrease with distance. Hence, the echo you hear is weaker than the original sound.
Answer to Question 2
Answer: Resonance is the response of any system when a forcing frequency matches its natural frequencyproducing an increase of amplitude. An example is someone pushing another person on a swing. When the pushes are in rhythm with the natural swing motion, the swing soon is high in the air with little effort by the person doing the pushing. Other examples are the sounding of a tuning fork by the vibrations of another nearby tuning fork of matched frequency and the destruction of a bridge when small pushes, stepping or gusts of wind, are applied in rhythm with the natural frequency of the bridge.
The original Neandertal remains from the Neander Valley, Germany.
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Original Horizontality