Gravity is the force responsible for the motion of a ball falling from a shelf to the floor. As the ball is released, gravity pulls it downward, causing it to accelerate towards the floor. References:
* Integrated Physical Sciences, Chapter 3: Forces and Motion

Energy is released to the surroundings during phase changes from higher energy states to lower energy states, such as from liquid to solid (freezing). When rain turns into ice upon hitting a cold surface, it undergoes freezing, a process in which the liquid water loses energy to the surroundings, releasing heat as it becomes solid ice.
References:
* Integrated Physical Sciences documents on phase changes and energy transfer.
* Thermodynamics principles in phase transitions.

* Wave propagation: Waves can travel through different mediums. Some waves, like sound and water waves, require a medium to propagate.
* Vacuum travel: Electromagnetic waves, including radio waves, can travel through a vacuum. This is because they do not require a medium; they propagate through the oscillation of electric and magnetic fields.
* Conclusion: The type of wave that can travel through a vacuum is a radio wave.
References: Integrated Physical Sciences materials on wave propagation, properties of electromagnetic waves, differences between mechanical and electromagnetic waves.

The scenario describes a geothermal energy system. Geothermal energy harnesses the heat from the Earth's interior to generate steam, which can then be used to produce electricity or provide direct heating. In this case, underground pipes circulate water that is heated by the Earth's internal heat, turning it into steam to generate heat for a building. References:
* U.S. Department of Energy (DOE) Geothermal Technologies Office
* "Geothermal Energy: Clean Power from the Earth's Heat" - National Renewable Energy Laboratory (NREL)

The statement that if the distance between a light source and an observer is doubled, the intensity of the light decreases by a factor of four, describes a consistent, repeatable observation that has been confirmed through numerous experiments. This describes a scientific law, specifically the inverse square law of light. A law summarizes a pattern found in nature, whereas a hypothesis is an untested prediction, a theory is a well-substantiated explanation, and an inference is a conclusion drawn from evidence. References:
* Integrated Physical Sciences, Chapter 4: Scientific Laws and Theories