Acceleration is always in the direction of the net unbalanced force.
Explanation
The relationship between force and acceleration is defined by Newton's Second Law of Motion. It states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. The mathematical representation is given by the vector equation:
$\vec{F}_{net} = m\vec{a}$
Where $\vec{F}_{net}$ is the net force, $m$ is the mass, and $\vec{a}$ is the acceleration.
Option Analysis:
- Acceleration is always in the direction of the velocity. is Incorrect. Acceleration is not necessarily in the direction of velocity. For example, when an object slows down (retardation), acceleration is opposite to velocity. In uniform circular motion, acceleration is perpendicular to the velocity.
- Acceleration is always in the direction of the net unbalanced force. is Correct. Since mass ($m$) is a positive scalar quantity, the direction of the acceleration vector ($\vec{a}$) is always determined by and identical to the direction of the net unbalanced force vector ($\vec{F}_{net}$).
- Acceleration is inversely proportional to the force. is Incorrect. According to the formula $a = F/m$, acceleration is directly proportional to the applied force, not inversely proportional.
- Acceleration is independent of the mass of the object. is Incorrect. Acceleration is inversely proportional to the mass of the object ($a \propto 1/m$). A larger mass results in smaller acceleration for the same applied force.
Key Takeaway:
Acceleration is a vector quantity that always acts in the direction of the net unbalanced force, regardless of the direction of the object's motion (velocity).