In the air, there's nothing holding the body of the helicopter still - so the rotor blades spin one direction, but the torque applied to spin the rotors tries to spin the body of the helicopter in the opposite direction. The little rotor on the tail helps keep the body of the helicopter pointed in the same direction.

The two vectors (say A and B) of different magnitudes cannot be combined to give zero resultant since minimum value of combination is ІA-BІ which is not zero if AB.

The three vectors A, B and C of different magnitudes can be zero such that they form a closed triangle, then,

      A+B+C=0

or, C=-(A+B)

Hence, the sum of three vectors may be zero if vector sum of any two vectors is equal and opposite to the third vector.

Note: The vectors can give this result only if...

According to the Heisenberg Uncertainty Principle, it is impossible to determine the exact spin of an electron at any given moment. The Uncertainty Principle states that the more precisely we know the position of a particle, the less precisely we can know its momentum, and vice versa. Spin is a form of intrinsic angular momentum, which means it does not correspond to any specific position in space, and therefore cannot be measured precisely at the same time as its position.

However, while we...

Compounds with hydrogen bonding tend to have higher melting and boiling points because the hydrogen bonding leads to stronger intermolecular forces. Intermolecular forces are the attractive forces between molecules, and they affect the physical properties of a substance, including melting and boiling points.

Hydrogen bonding is a particularly strong type of intermolecular force that occurs when a hydrogen atom is bonded to a highly electronegative atom such as nitrogen, oxygen, or fluorine....