Explanation:
Boiling water requires the input of heat energy. When heat energy is added to water, it causes the water molecules to gain energy and move faster. As a result, the water temperature increases and eventually reaches its boiling point.

Heat energy:
Heat energy is a form of energy that can be transferred from one object to another due to a temperature difference. It is the energy associated with the motion of particles within a substance. When heat energy is added to a substance, the particles within the substance gain energy and move faster.

Boiling water:
When water is heated, its temperature rises. As the temperature of the water approaches its boiling point, the heat energy causes the water molecules to move more rapidly. At the boiling point, the heat energy overcomes the forces of attraction between the water molecules, and the water begins to vaporize and turn into steam. This process is known as boiling.

Other forms of energy:
- Electric energy: Electric energy can be used to heat water. Electric kettles, for example, use electric energy to heat the water inside them. The electric energy is converted into heat energy, which raises the temperature of the water.
- Mechanical energy: Mechanical energy can also be used to heat water indirectly. For example, a mechanical device such as a water pump can be used to circulate hot water through a system, heating the water as it moves.

Conclusion:
In conclusion, boiling water requires the input of heat energy. While electric energy and mechanical energy can be used to transfer heat energy to the water, the fundamental energy required for boiling is heat energy.

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