# A block of mass m lies on a horizontal table. The coefficient of static friction between the...

## Question:

A block of mass m lies on a horizontal table. The coefficient of static friction between the block and the table is mus. The coefficient of kinetic friction is {eq}\mu_k {/eq}, with {eq}\mu_k < \mu_s {/eq}.

a. If the block is at rest (and the only forces acting on the block are the force due to gravity and the normal force from the table), what is the magnitude of the force due to friction?

b. Suppose you want to move the block, but you want to push it with the least force possible to get it moving. With what force F must you be pushing the block just before the block beings to move?

c. Suppose you push horizontally with precisely enough force to just make the block move. What is the magnitude of the friction force?

d. Suppose you push horizontally with precisely enough force to make the block start to move, and you continue to apply the same amount of force even after it starts moving. Find the acceleration of the block after it begins to move.

## Static and Dynamic Friction:

Static friction is the friction of a body that resists motion. Kinetic friction is the friction of a body that retards motion. The two are differentiated by their different coefficients.

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#### Part (a)

{eq}F = \boxed{\mu_s mg} {/eq}

When the body is at rest, the friction we are concerned about is static friction.

#### Part (b)

{eq}F =... Coefficient of Friction: Definition, Formula & Examples

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Chapter 11 / Lesson 21
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The concept of coefficient of friction may be confusing, but don't fret. Come inside to discover what the coefficient of friction is, how it is calculated, and to see some examples of this coefficient for a few common surfaces.