Tidal forces are the gravitational effects that one celestial body exerts on another, causing changes in shape and movement. These forces are most commonly observed between the Earth and the Moon, where the Moon's gravity pulls on the Earth's oceans, creating high and low tides. The strength of tidal forces depends on the distance between the two bodies and their masses. When the Sun is also considered, its gravitational pull can enhance or diminish the tides, leading to spring tides (higher high tides) and neap tides (lower high tides) depending on the alignment of the Earth, Moon, and Sun.