Hi all, I was puzzled by the answers offered by an assessment book on this 2 questions. Hope fellow forummers can help me out on this please. 1. A thin steel card is made to vibrate by holding it against the teeth of a cog wheel. The wheel is rotated with increasing speed. The sound wave is displayed on a cathode-ray oscilloscope. The question being asked is basically: what features of the sound will change as the steel card is hit with increasing speed. I would think that the answer is pitch (higher) and loudness (higher). But the answer offered by the book is pitch only. I am puzzled why loudness of sound is not increased. When i hit something quicker, i would think that more force is being imparted into the object. Does not an increase in speed translate to a preceding increase in force needed to make the wheel turn faster? 2. A string is suspended with a weight tied to its end. The string is then reduced to a quarter of its original length, while the attached weight is reduced to half. The question asked whether the new setup will have a higher or lower pitch sound. The answer is higher pitch. My question is, does the weight attached and the length of the string follow a direct proportion relationship? In other words, if i half the length of the string, and half the attached weight, does the pitch of the sound stay the same? Hope forummers can help out this troubled physics teacher.