Q6CQ - College Physics (Urone)

Question

 Why can we neglect forces such as those holding a body together when we apply Newton’s second law of motion?

Step-by-Step Solution

Answer

Internal forces acting on a body are equal and opposite in direction, so their sum must be zero. Therefore, there can be no net force from the internal forces.

Step 1: Concept of Newton’s second law of motion

Newton’s second law of motion states that the acceleration of a system is directly proportional to the net external force acting on the system and is inversely proportional to the mass of the system. Mathematically,

$F_{net} =ma$

Here${}^{F_{net}}$ is the net force,${}^m$is the mass, and${}^a$is the acceleration.

Step 2: Explanation for neglecting the internal forces

According to Newton’s first law, the change in motion is due to the net external force. Internal forces are responsible for holding together a given body. The internal forces do not affect the motion of a body. The motion of a body is affected only by external forces.

Internal forces acting on a body are equal and opposite in direction, so their sum must be zero. Therefore, there can be no net force from the internal forces.