Question

A stone is tied to a string and whirled such that the stone performs horizontal circular motion. It can be seen that the string is NEVER horizontal.

Answer 1

The string is never horizontal because the stone has weight mg acting vertically downward.

For the stone to move in a horizontal circle, the tension T in the string must have:

Vertical component: Balances the weight of the stone,

T cos θ = mg

Horizontal component provides the centripetal force,

T sin θ = `(m v^2)/r`

Therefore, the string must remain inclined to the vertical. If it became horizontal, tension would have no upward component to balance the weight, so horizontal circular motion would not be possible.