Experiment 3: Kinetic and Static Friction — Worked Examples

A $1.20\,\text{kg}$ block begins to move when a horizontal spring-balance reading reaches $5.40\,\text{N}$. Determine $\mu_s$ using $g=9.80665\,\text{m/s}^2$.

The same block requires a steady horizontal pull of $4.10\,\text{N}$ to move at approximately constant velocity. Determine $\mu_k$.

A $0.300\,\text{kg}$ mass is placed on the $1.20\,\text{kg}$ block. If $\mu_k=0.348$, predict the kinetic friction force for a horizontal pull.

A dry surface pair has $\mu_s=0.459$. Determine the ideal incline angle at which the block is just about to slide.

If $\mu_k=0.348$, at what ideal incline angle would a sliding block move with zero acceleration?

A best-fit graph of measured kinetic friction $f_k$ on the vertical axis versus normal force $N$ on the horizontal axis has slope $0.372$ and intercept $0.06\,\text{N}$. Interpret the result.

A $1.00\,\text{kg}$ block moves at constant velocity while pulled by $F=4.00\,\text{N}$ at $15^\circ$ above horizontal. Determine $\mu_k$.

Two trials on the same surface give $(N,f_k)=(8.0\,\text{N},2.9\,\text{N})$ and $(14.0\,\text{N},5.1\,\text{N})$. Determine the coefficient in each trial and comment on consistency.