In pure rolling, the bottommost point has zero velocity wrt ground...and as there is no relative motion between the ground and the point, no friction acts..but that point has a tendency to move ahead and let another point take its place...so that means static friction must act right?

That's a thoughtful observation about pure rolling motion! Let's break it down to clarify how static friction operates in this scenario.

Understanding Pure Rolling Motion

In pure rolling, an object, like a wheel or a ball, rolls without slipping. This means that the point of contact with the ground does not slide; instead, it momentarily comes to rest as it touches the surface. The bottommost point of the rolling object indeed has zero velocity relative to the ground at that instant.

The Role of Static Friction

Now, regarding static friction, it's essential to recognize its function in rolling motion. While the bottom point of the wheel is not moving relative to the ground, the wheel itself is rotating. This rotation creates a tendency for the wheel to continue moving forward, which you correctly noted. However, because the bottom point is stationary with respect to the ground, static friction is what prevents slipping from occurring.

• Static Friction Prevents Slipping: Static friction acts at the point of contact to ensure that the wheel rolls smoothly without sliding. If there were no static friction, the wheel would slip instead of rolling.
• Forward Motion: As the wheel rolls, the static friction force acts in the direction opposite to the wheel's tendency to slide backward. This force allows the wheel to accelerate forward.
• Energy Transfer: Static friction also plays a crucial role in transferring energy from the ground to the wheel, enabling it to roll forward effectively.

Illustrative Example

Imagine a bicycle wheel rolling down a hill. At the point where the tire meets the ground, the tire is not sliding; it's momentarily at rest. However, as the wheel rotates, the next point on the tire takes its place at the bottom. Static friction ensures that this transition happens smoothly, allowing the wheel to continue rolling without losing grip.

Conclusion on Static Friction in Rolling

In summary, while the bottommost point of a rolling object has zero velocity relative to the ground, static friction is indeed at play. It acts to prevent slipping and facilitates the rolling motion. Without static friction, the wheel would not be able to roll effectively, and instead, it would slide. So, your reasoning about the necessity of static friction in this context is spot on!