The formula to calculate the friction force is:
\[ F = U \times N \]
Where:
Let's say the coefficient of friction (U) is 0.5 and the normal force (N) is 100 N. Using the formula:
\[ F = 0.5 \times 100 \]
We get:
\[ F = 50\, \text{N} \]
So, the friction force is 50 N.