Explain why Sliding Friction is Less Than Static Friction

Explain why Sliding Friction is Less Than Static Friction

Friction, the force that opposes motion between two surfaces in contact, is a phenomenon that affects our daily lives in numerous ways.

When discussing friction, it is crucial to understand the differences between static friction and sliding friction. 

In this article, we will delve into the intricacies of these two types of friction and explore why sliding friction is typically lower than static friction, unveiling the underlying mechanisms responsible for this intriguing phenomenon.

Why Sliding Friction is Less Than Static Friction:

Sliding friction is typically less than static friction due to surface interactions and microscopic factors.

When two surfaces are at rest, their microscopic irregularities and asperities interlock, creating a stronger bond and higher resistance to motion (static friction).

During sliding motion, these interlocking points are broken, reducing the contact area and weakening the intermolecular forces between surfaces.

This leads to lower resistance to motion and a decrease in frictional force (sliding friction). Additionally, energy considerations and velocity dependency further contribute to the lower magnitude of sliding friction compared to static friction.

1. Static Friction and Sliding Friction: Definitions and Characteristics:

Static friction is the force that prevents an object from initiating motion when an external force is applied. It comes into play when two stationary surfaces are in contact. 

On the other hand, sliding friction, also known as kinetic friction, arises when two surfaces are in relative motion against each other.

The key characteristic of static friction is that it adjusts its magnitude according to the applied force, preventing motion until the force surpasses a certain threshold. Sliding friction, however, remains relatively constant once motion is initiated.

2. Surface Interactions and Microscopic Factors:

The primary reason why sliding friction is generally lower than static friction lies in the interactions between the surfaces and microscopic factors at play.

When two stationary surfaces come into contact, their microscopic irregularities and asperities interlock, creating a substantial number of contact points.

These interlocking points generate a stronger bond, resulting in higher resistance to motion—i.e., static friction.

During sliding motion, the interlocking points are broken, and the surfaces' asperities glide over each other.

As a result, the overall contact area decreases, reducing the number of intermolecular forces acting between the surfaces.

This reduction in intermolecular forces decreases the resistance to motion, leading to a lower frictional force.

3. Energy Considerations:

To further comprehend the disparity between static and sliding friction, let's consider the energy aspects associated with these two types of friction.

In the case of static friction, energy is required to overcome the intermolecular forces and deform the surfaces slightly, allowing them to slide. This energy is stored within the system and contributes to the higher static frictional force.

During sliding friction, the energy is dissipated in the form of heat due to the constant breaking and reforming of intermolecular bonds.

As a result, the overall frictional force acting between the surfaces in relative motion decreases, leading to lower sliding friction.

4. Velocity Dependency:

Another critical factor that distinguishes static friction from sliding friction is their dependence on velocity.

Static friction remains constant until the applied force reaches its maximum limit, at which point motion is initiated.

Sliding friction, on the other hand, is relatively independent of velocity as long as the surfaces continue to slide at a constant speed.

While an increase in speed might result in a slight rise in sliding friction due to factors such as air resistance, it remains significantly lower than static friction.

This characteristic enables objects in motion to maintain a relatively constant level of frictional resistance, making it easier to sustain movement.

Conclusion:

In conclusion, the dissimilarity between static friction and sliding friction arises from the interactions between the surfaces, microscopic factors, energy considerations, and velocity dependency.

Static friction, present between stationary surfaces, is higher due to intermolecular bonding and the increased contact area.

Sliding friction, occurring during relative motion, involves reduced contact area and energy loss, leading to lower frictional force.