How does a change in frequency or amplitude change the sound we hear?

Here, Amplitude mainly describes the intensity of sound we hear, They are directly proportional to each other. In other words, If Amplitude of the sound in greater, then you'll hear loud sound, vice-versa.

Frequency is the pitch of a sound. Change in frequency will change the pitch, and particularly for intensity, it doesn't affect loudness of the sound

Hope this helps!

The troposphere gets warmer as altitude increases.

When the ball is rising up, it gains kinetic energy. when the ball reaches the very top, it will have all potential energy, until it falls back down and gains it kinetic energy. finally when you catch the ball or it falls back down, it would have gained its potential energy back.