Kinetic and Static Friction - AP Physics C: Mechanics
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If $\mu_s = 0.3$ and $\mu_k = 0.25$, which is larger?
If $\mu_s = 0.3$ and $\mu_k = 0.25$, which is larger?
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$\mu_s$. Static coefficient (0.3) exceeds kinetic coefficient (0.25).
$\mu_s$. Static coefficient (0.3) exceeds kinetic coefficient (0.25).
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Identify the unit of friction coefficients.
Identify the unit of friction coefficients.
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Unitless. Coefficients are dimensionless ratios of forces.
Unitless. Coefficients are dimensionless ratios of forces.
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If $\mu_s = 0.3$ and $\mu_k = 0.25$, which is larger?
If $\mu_s = 0.3$ and $\mu_k = 0.25$, which is larger?
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$\mu_s$. Static coefficient (0.3) exceeds kinetic coefficient (0.25).
$\mu_s$. Static coefficient (0.3) exceeds kinetic coefficient (0.25).
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What is the maximum static friction force called?
What is the maximum static friction force called?
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Limiting static friction. This is the maximum value static friction can reach.
Limiting static friction. This is the maximum value static friction can reach.
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Calculate $\mu_k$ if $f_k = 15 \text{N}$ and $F_n = 75 \text{N}$.
Calculate $\mu_k$ if $f_k = 15 \text{N}$ and $F_n = 75 \text{N}$.
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$\mu_k = 0.2$. Using $\mu_k = \frac{f_k}{F_n} = \frac{15}{75} = 0.2$.
$\mu_k = 0.2$. Using $\mu_k = \frac{f_k}{F_n} = \frac{15}{75} = 0.2$.
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Define the coefficient of static friction.
Define the coefficient of static friction.
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The ratio of maximum static friction to the normal force. It quantifies the material's resistance to starting motion.
The ratio of maximum static friction to the normal force. It quantifies the material's resistance to starting motion.
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What effect does increasing normal force have on friction?
What effect does increasing normal force have on friction?
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Increases frictional force. Friction is directly proportional to normal force.
Increases frictional force. Friction is directly proportional to normal force.
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Identify whether friction opposes or assists motion.
Identify whether friction opposes or assists motion.
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Opposes motion. Friction always acts to resist relative motion.
Opposes motion. Friction always acts to resist relative motion.
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Define the coefficient of kinetic friction.
Define the coefficient of kinetic friction.
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The ratio of kinetic friction to the normal force. It quantifies the resistance during sliding motion.
The ratio of kinetic friction to the normal force. It quantifies the resistance during sliding motion.
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For an object on a flat surface, what is the normal force equal to?
For an object on a flat surface, what is the normal force equal to?
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Equal to the gravitational force on the object. On level ground, normal force equals weight $mg$.
Equal to the gravitational force on the object. On level ground, normal force equals weight $mg$.
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Find the kinetic friction force if $\mu_k = 0.3$ and $F_n = 100 \text{N}$.
Find the kinetic friction force if $\mu_k = 0.3$ and $F_n = 100 \text{N}$.
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$f_k = 30 \text{N}$. Using $f_k = \mu_k F_n = 0.3 \times 100 = 30$ N.
$f_k = 30 \text{N}$. Using $f_k = \mu_k F_n = 0.3 \times 100 = 30$ N.
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Find $f_k$ if $\mu_k = 0.25$ and $F_n = 400 \text{N}$.
Find $f_k$ if $\mu_k = 0.25$ and $F_n = 400 \text{N}$.
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$f_k = 100 \text{N}$. Using $f_k = \mu_k F_n = 0.25 \times 400 = 100$ N.
$f_k = 100 \text{N}$. Using $f_k = \mu_k F_n = 0.25 \times 400 = 100$ N.
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Find $f_s$ if $\mu_s = 0.6$ and $F_n = 150 \text{N}$.
Find $f_s$ if $\mu_s = 0.6$ and $F_n = 150 \text{N}$.
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$f_s \leq 90 \text{N}$. Maximum static friction is $\mu_s F_n = 0.6 \times 150 = 90$ N.
$f_s \leq 90 \text{N}$. Maximum static friction is $\mu_s F_n = 0.6 \times 150 = 90$ N.
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Determine the limiting static friction if $\mu_s = 0.5$ and $F_n = 100 \text{N}$.
Determine the limiting static friction if $\mu_s = 0.5$ and $F_n = 100 \text{N}$.
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$f_s = 50 \text{N}$. Maximum static friction is $\mu_s F_n = 0.5 \times 100 = 50$ N.
$f_s = 50 \text{N}$. Maximum static friction is $\mu_s F_n = 0.5 \times 100 = 50$ N.
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Find $f_k$ if $\mu_k = 0.15$ and $F_n = 300 \text{N}$.
Find $f_k$ if $\mu_k = 0.15$ and $F_n = 300 \text{N}$.
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$f_k = 45 \text{N}$. Using $f_k = \mu_k F_n = 0.15 \times 300 = 45$ N.
$f_k = 45 \text{N}$. Using $f_k = \mu_k F_n = 0.15 \times 300 = 45$ N.
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What is the role of friction in walking?
What is the role of friction in walking?
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Prevents slipping by providing traction. Static friction between feet and ground enables forward motion.
Prevents slipping by providing traction. Static friction between feet and ground enables forward motion.
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Calculate $\mu_k$ if $f_k = 15 \text{N}$ and $F_n = 75 \text{N}$.
Calculate $\mu_k$ if $f_k = 15 \text{N}$ and $F_n = 75 \text{N}$.
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$\mu_k = 0.2$. Using $\mu_k = \frac{f_k}{F_n} = \frac{15}{75} = 0.2$.
$\mu_k = 0.2$. Using $\mu_k = \frac{f_k}{F_n} = \frac{15}{75} = 0.2$.
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What is the effect of surface area on friction?
What is the effect of surface area on friction?
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No direct effect. Friction depends only on normal force and surface properties.
No direct effect. Friction depends only on normal force and surface properties.
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What effect does increasing normal force have on friction?
What effect does increasing normal force have on friction?
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Increases frictional force. Friction is directly proportional to normal force.
Increases frictional force. Friction is directly proportional to normal force.
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Identify the direction of frictional force relative to motion.
Identify the direction of frictional force relative to motion.
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Opposite to motion or impending motion. Friction always opposes relative motion between surfaces.
Opposite to motion or impending motion. Friction always opposes relative motion between surfaces.
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What is the maximum static friction force called?
What is the maximum static friction force called?
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Limiting static friction. This is the maximum value static friction can reach.
Limiting static friction. This is the maximum value static friction can reach.
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Identify the unit of friction coefficients.
Identify the unit of friction coefficients.
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Unitless. Coefficients are dimensionless ratios of forces.
Unitless. Coefficients are dimensionless ratios of forces.
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What is the formula for kinetic frictional force?
What is the formula for kinetic frictional force?
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$f_k = \mu_k F_n$. Kinetic friction has a constant magnitude proportional to normal force.
$f_k = \mu_k F_n$. Kinetic friction has a constant magnitude proportional to normal force.
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Which is generally larger: static or kinetic friction coefficient?
Which is generally larger: static or kinetic friction coefficient?
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Static friction coefficient. It's harder to start motion than to maintain it.
Static friction coefficient. It's harder to start motion than to maintain it.
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For an object on a flat surface, what is the normal force equal to?
For an object on a flat surface, what is the normal force equal to?
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Equal to the gravitational force on the object. On level ground, normal force equals weight $mg$.
Equal to the gravitational force on the object. On level ground, normal force equals weight $mg$.
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Calculate friction if $\mu_k = 0.1$ and $F_n = 200 \text{N}$.
Calculate friction if $\mu_k = 0.1$ and $F_n = 200 \text{N}$.
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$f_k = 20 \text{N}$. Using $f_k = \mu_k F_n = 0.1 \times 200 = 20$ N.
$f_k = 20 \text{N}$. Using $f_k = \mu_k F_n = 0.1 \times 200 = 20$ N.
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What is the formula for static frictional force?
What is the formula for static frictional force?
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$f_s , \leq , \mu_s F_n$. This inequality shows static friction can range from zero up to its maximum value.
$f_s , \leq , \mu_s F_n$. This inequality shows static friction can range from zero up to its maximum value.
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What is the formula for static frictional force?
What is the formula for static frictional force?
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$f_s , \leq , \mu_s F_n$. This inequality shows static friction can range from zero up to its maximum value.
$f_s , \leq , \mu_s F_n$. This inequality shows static friction can range from zero up to its maximum value.
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Identify if kinetic friction can do work.
Identify if kinetic friction can do work.
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Yes, kinetic friction can do work. Kinetic friction acts through displacement, doing negative work.
Yes, kinetic friction can do work. Kinetic friction acts through displacement, doing negative work.
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Can static friction do work on an object?
Can static friction do work on an object?
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No, static friction does not do work. Static friction prevents motion, so displacement is zero.
No, static friction does not do work. Static friction prevents motion, so displacement is zero.
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