Answer: Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: Dry friction is a force that opposes the relative lateral motion of two solid surfaces in contact
It does produce 'sound' ... a compression wave traveling through the air. But your ears don't hear a sound that's vibrating less than 20 or 30 times every second. If you could swing your pendulum that fast, you could hear the sound of its vibrations pushing the air around.
Waves transmit energy without transmitting matter, This means that we can move energy or information from one place to another without moving any substance from one place to another.
Answer: it would be A
Explanation: how are we to measure the air of a square mile
To solve this problem we will apply the concepts related to the balance of Forces, the centripetal Force and Newton's second law.
I will also attach a free body diagram that allows a better understanding of the problem.
For there to be a balance between weight and normal strength, these two must be equivalent to the centripetal Force, therefore


Here,
m = Net mass
= Angular velocity
r = Radius
W = Weight
N = Normal Force

The net mass is equivalent to

Then,

Replacing we have then,

Solving to find the angular velocity we have,

Therefore the angular velocity is 0.309rad/s