If a moving with a constant velocity, there will be zero acceleration , according to 2nd law F=ma,

Now a= 0

F=m×0

F=0

If the force will be zero than, how can body in motion?

It's a common misconception to think that if an object is in motion and has zero acceleration, it must mean that no forces are acting on it. Let's break this down to clarify how motion and forces interact, especially in the context of Newton's laws of motion.

Understanding Motion and Forces

According to Newton's first law of motion, an object will remain at rest or in uniform motion in a straight line unless acted upon by a net external force. This means that if an object is moving at a constant velocity, it is not accelerating, but that doesn't imply that there are no forces acting on it.

Constant Velocity and Forces

When an object moves with constant velocity, it means that its speed and direction are not changing. In this case, the acceleration (a) is indeed zero. However, this does not mean that the net force (F) acting on the object is zero. Instead, it indicates that all the forces acting on the object are balanced.

• Balanced Forces: If an object is moving at a constant velocity, the forces acting on it are equal in magnitude but opposite in direction. For example, if a car is cruising at a steady speed on a flat road, the forward force from the engine is balanced by the resistive forces such as friction and air resistance.
• Net Force: The net force is the vector sum of all the forces acting on an object. If these forces balance out, the net force is zero, leading to no acceleration. However, this does not prevent the object from moving.

Example: A Car on the Highway

Consider a car driving on a straight highway at a constant speed of 60 km/h. The engine generates a forward force to propel the car. At the same time, friction from the tires on the road and air resistance oppose this motion. If the forward force from the engine equals the sum of the opposing forces, the net force is zero, and the car continues to move at that constant speed.

Applying Newton's Second Law

Newton's second law, expressed as F = ma, tells us that the net force acting on an object is equal to the mass of the object multiplied by its acceleration. When acceleration is zero (a = 0), it follows that:

F = m × 0 = 0

This equation indicates that the net force is zero, but it does not mean that all forces are absent. Instead, it confirms that the forces are balanced, allowing the object to maintain its state of motion.

Real-World Implications

This principle is crucial in various real-world applications, such as in engineering and physics. For instance, when designing vehicles, engineers must account for forces like drag and friction to ensure that the vehicle can maintain a desired speed without accelerating or decelerating.

Final Thoughts

In summary, an object can be in motion with zero acceleration when the forces acting on it are balanced. The presence of forces does not necessarily result in acceleration; it depends on whether those forces are balanced or unbalanced. Understanding this concept is key to grasping the fundamentals of dynamics and motion in physics.