In a laboratory experiment on friction, a 135-N block resting on a rough horizontal table is pulled by a horizontal wire. The pull gradually increases until the block begins to move and continues to increase thereafter. Figure E5.26 shows a graph of the friction force on this block as a function of the pull. (a) Identify the regions of the graph where static friction and kinetic friction occur.

Verified step by step guidance

1. Observe the graph and note that the friction force (f) is plotted on the y-axis and the pulling force (F) is plotted on the x-axis.
2. Identify the region where the friction force increases linearly with the pulling force. This region represents static friction, where the block is not yet moving.
3. Locate the point on the graph where the friction force reaches its maximum value. This point represents the maximum static friction force, beyond which the block starts to move.
4. Identify the region after the maximum static friction force where the friction force remains constant despite an increase in the pulling force. This region represents kinetic friction, where the block is moving.
5. Label the regions on the graph: the initial linear increase as static friction and the constant region after the peak as kinetic friction.

Key Concepts

Static Friction

Static friction is the force that prevents an object from starting to move when a force is applied. It acts in the opposite direction of the applied force and increases up to a maximum value, known as the static friction limit. In the graph, this is represented by the initial rising section where the friction force increases with the applied pull force until the block begins to move.

Kinetic Friction

Kinetic friction occurs when an object is already in motion. It is generally less than static friction and remains relatively constant regardless of the applied force, as long as the object continues to slide. In the graph, this is shown by the horizontal section after the block starts moving, indicating that the friction force stabilizes at a lower value compared to the maximum static friction.

Friction Force Graph

A friction force graph plots the relationship between the applied force and the friction force experienced by an object. The shape of the graph provides insights into the behavior of static and kinetic friction. In this case, the graph illustrates the transition from static to kinetic friction, highlighting the maximum static friction point and the constant kinetic friction force that follows.