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How long will a ball, say a billiard ball, stop rolling on a flat surface for a given coefficient of friction? What is the formula for the ball's decreasing velocity?

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 Time to stop is  initial_speed/(mu * g)

Derivation below.

Assume the ball is moving to the right, then the free body diagram is

Mathematica graphics

The equation of motion is $$ m\ddot{x} = -\mu N $$ But \$ N = mg \$ hence $$ \ddot{x} = -\mu g $$ Using the constant acceleration kinematic equation $$ \dot{x}_{final} = \dot{x}_{initial} + \ddot{x}t = \dot{x}_{initial} - \mu gt$$ Then, by letting final speed be zero, we solve for the time for the ball to stop. $$ t= \frac{\dot{x}_{initial}}{\mu g}$$ For example, using coefficient of friction \$ \mu = 0.15 \$, initial speed of \$ \dot{x} = 15 \$ meters per second and earth's gravity \$ g=9.81 \$, then the time to stop is $$ t = \frac{15}{(0.15)(9.81)} = 10.2 s$$

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  • \$\begingroup\$ Latex is not supported. Some of the stack exchange sites support MathJax, but GDSE is not currently one of them. There's a meta post regarding adding MathJax support to GDSE. If it would have helped your question, vote accordingly. \$\endgroup\$
    – Pikalek
    Oct 10 '17 at 2:50

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