You are waiting for your friend to give you a ride on his new motorcycle. as your friend pulls up the driveway the brakes squeal loudly. you get on, and then your friend steps on the engine. as the motorcycle accelerates, the engine roars loudly. the high-pitched squeal of the brakes was caused by sound waves, and the equally loud but low-pitched roar of the engine was caused by sound waves.

The high pitched squeal of the brakes is caused by high-frequency sounds waves, which could be as high as 20,000 Hz. The loud roar of the engine is low-frequency sound waves, which could be as low as 20 Hz. Humans can hear within that range of sounds and while the volume might be the same the pitch is different based on the frequency of the sound.

Is a  vector quantity  that refers to "the rate at which an object changes its position." imagine a person moving rapidly - one step forward and one step back - always returning to the original starting position. while this might result in a frenzy of activity, it would result in a zero velocity. because the person always returns to the original position, the motion would never result in a change in position. since velocity is defined as the rate at which the position changes, this motion results in zero velocity. if a person in motion wishes to maximize their velocity, then that person must make every effort to maximize the amount that they are displaced from their original position. every step must go into moving that person further from where he or she started. for certain, the person should never change directions and begin to return to the starting position.