during pure rolling where does static fric act and why does body not accelerate or decelerate.

When we talk about pure rolling motion, such as a wheel rolling on a surface without slipping, it's essential to understand the role of static friction and why the object maintains a constant velocity. Let's break this down step by step.

Understanding Pure Rolling Motion

In pure rolling, a wheel or cylinder rolls over a surface without any sliding. This means that the point of contact between the wheel and the ground is momentarily at rest relative to the ground. The key here is that static friction is what allows this type of motion to occur.

The Role of Static Friction

Static friction acts at the point of contact between the wheel and the surface. Its primary function is to prevent slipping. When a wheel rolls, the static frictional force provides the necessary torque that allows the wheel to rotate. This force arises because the wheel's center of mass moves forward while the point of contact does not slide on the surface.

• Prevention of Slipping: Static friction ensures that the wheel rolls without slipping, meaning the velocity of the center of mass of the wheel is equal to the velocity of the point of contact.
• Torque Generation: The static friction provides the torque needed for the wheel to rotate. If the friction were to be kinetic (which happens during sliding), the wheel would not roll smoothly.

Why No Acceleration or Deceleration?

In pure rolling motion, the wheel does not accelerate or decelerate because the forces acting on it are balanced. Here’s how it works:

• Net Force: If the wheel is rolling at a constant speed, the net external force acting on it is zero. This means that any forces trying to accelerate the wheel are balanced by other forces, such as friction or resistance.
• Constant Velocity: According to Newton's first law of motion, an object in motion will stay in motion at a constant velocity unless acted upon by an unbalanced force. In pure rolling, the static friction does not change the speed of the wheel; it only facilitates the rolling motion.

Example for Clarity

Imagine a bicycle tire rolling on a flat road. The tire's contact point with the road is stationary at that instant, thanks to static friction. As the bike moves forward, the tire rotates, and the static friction ensures that the tire rolls smoothly without slipping. If the cyclist maintains a steady pedaling speed, the bike continues to move forward at a constant velocity, illustrating how static friction allows for pure rolling without acceleration or deceleration.

Final Thoughts

In summary, during pure rolling, static friction acts at the contact point to prevent slipping and facilitate rotation. The absence of acceleration or deceleration is due to the balance of forces acting on the wheel, allowing it to maintain a constant velocity. This interplay of forces is crucial for understanding the dynamics of rolling objects in physics.