The force is extremely weak due to the small value of $G$.
Explanation
According to Newton's Law of Universal Gravitation, the force ($F$) of attraction between two objects is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. The equation is expressed as:
$F = G \frac{m_1 m_2}{r^2}$
Here, $G$ represents the Universal Gravitational Constant.
Option Analysis
- The force is repulsive. is Incorrect: Gravitational force is inherently attractive. It never acts as a repulsive force.
- The force is extremely weak due to the small value of $G$. is Correct: The value of the Universal Gravitational Constant ($G$) is extremely small, approximately $6.67 \times 10^{-11} \, \text{Nm}^2/\text{kg}^2$. When calculating the force between ordinary objects (like two people), the product of their masses is relatively small. When this product is multiplied by the tiny value of $G$, the resulting force is negligible (on the order of $10^{-7}$ Newtons). This magnitude is too small to be perceived by human senses or to overcome everyday resistive forces.
- Friction cancels it out. is Incorrect: While static friction often prevents the motion that this weak force might cause, it is not the fundamental reason the force is imperceptible. The imperceptibility stems from the magnitude of the force itself.
- Atmospheric pressure cancels it out. is Incorrect: Atmospheric pressure acts uniformly on objects but does not negate or cancel the gravitational attraction between two distinct masses.
Key Takeaway: Gravitation is the weakest of the four fundamental forces. Its effects are only perceptible or significant when at least one of the masses involved is astronomical in scale (e.g., Earth), due to the extremely low value of the gravitational constant $G$.