Earth pulls it downward to the gravitational force
21/12 is equal to 1 3/4 hope this helps!
The friction force is given by:

Where μ is the coefficient of friction (static or kinetic) and

is the normal force. So we say the friction force is directly proportional to the normal force with a constant of proportionality equal to the coefficient of friction.
Based on the options given, the most likely answer to this query is
B) as volume decreases, temperature decreases.
Charles' law states that when volume increase or decrease, accordingly, temperature becomes similar.
Thank you for your question. Please don't hesitate to ask in Brainly your queries.
Answer:
A modern piano has 88 keys and is tuned to twelve-tone equal temperament. It has its 49th key, the fifth A, also called A4, tuned to a frequency of 440 Hz (referred to as A440).