Final answer:
The gravitational force of the Sun on Earth is stronger in December than in June due to Earth's elliptical orbit bringing it closer to the Sun in early January. However, the Earth's axial tilt, not its distance from the Sun, causes the seasons.
Step-by-step explanation:
The force of gravity exerted by the Sun on the Earth in December compared to June is slightly stronger because Earth is closer to the Sun in early January and thus also in December. Newton's law of universal gravitation states that the force of gravity is inversely proportional to the square of the distance between two objects. Since the Earth's orbit is elliptical, we are about 3% closer to the Sun in January, and by extension in December, resulting in a slightly stronger gravitational pull.
It is a common misconception that the changing distance between the Earth and the Sun causes the seasons; however, the actual cause of the seasons is the 23.5° tilt of the Earth's axis. This tilt results in varying angles of sunlight and lengths of daylight, which create the seasons. Despite the closer proximity to the Sun in December for the Northern Hemisphere, it is winter because the hemisphere is tilted away from direct sunlight.