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Belt Friction

Statics · FE Reference Handbook section

Statics
5 formulas
10 exam-style examples
~55 min
All Statics lectures

Core formulas for this FE topic

Definitions, applicability, units, assumptions and worked examples for each relation.

Worked exam-style examples

The four ways this section is written on the real exam — thoughts first, then equations, then substitution.

Example 1
Coulomb friction — solve for friction force — Belt Friction

A statics problem uses Coulomb friction. Given friction coefficient (mu) = 0.6100; normal force (N) = 1,680 lb, determine the friction force (F) in lb.

Given

  • frictioncoefficient(mu)=0.6100friction coefficient (mu) = 0.6100
  • normalforce(N)=1,680lbnormal force (N) = 1,680 lb

Find

friction force (F), in lb

Start with the thinking

  • The governing relation printed in this handbook section is Coulomb friction.
  • Everything except F is given, so isolate F symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Statics items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    F=μNF = \mu N
  2. Step 2 — Rearrange the relation so that F stands alone on the left-hand side.

  3. Step 3

    Listthegivens:frictioncoefficient(mu)=0.6100,normalforce(N)=1,680lbList the givens: friction coefficient (mu) = 0.6100, normal force (N) = 1,680 lb
  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    F=1025 lbF = 1025\ \text{lb}
  6. Step 6 — Check: returning F = 1,025 lb to

    F=μNF = \mu N

    reproduces the given quantities, and both sides carry the same units.

Answer:
F=1025 lbF = 1025\ \text{lb}

Why the other options are there

  • 2,050 — kept a factor of two that cancels in the correct rearrangement.
  • 512.4 — dropped that same factor in the other direction.
  • 1,127 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Statics → Belt Friction

Example 2
Belt friction — solve for tight side tension — Belt Friction (2)

A rope wrapped around a capstan uses belt friction to hold a load. Given slack side tension (T_2) = 104.0 lbf; coefficient of friction (mu) = 0.2500; wrap angle (beta) = 1.6500 rad, determine the tight side tension (T_1) in lbf.

Given

  • slacksidetension(T2)=104.0lbfslack side tension (T_2) = 104.0 lbf
  • coefficientoffriction(mu)=0.2500coefficient of friction (mu) = 0.2500
  • wrapangle(beta)=1.6500radwrap angle (beta) = 1.6500 rad

Find

tight side tension (T_1), in lbf

Start with the thinking

  • The governing relation printed in this handbook section is Belt friction.
  • Everything except T_1 is given, so isolate T_1 symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Belt friction relates the tight-side and slack-side tensions across a pulley through the coefficient of friction and wrap angle.
T_1T_2Pulley

Figure 2 — schematic for Belt friction — solve for tight side tension — Belt Friction (2)

Step-by-step solution

  1. Step 1 — State the governing relation:

    T1=T2eμβT_1 = T_2 e^{\mu \beta}
  2. Step 2 — Rearrange symbolically for T_1:

    T1=T2eμβT_{1} = T_2 e^{\mu \beta}
  3. Step 3 — List the givens: slack side tension (T_2) = 104.0 lbf, coefficient of friction (mu) = 0.2500, wrap angle (beta) = 1.6500 rad.

  4. Step 4 — Substitute the given values:

    T1=T2e0.25001.6500T_{1} = T_2 e^{0.2500 1.6500}
  5. Step 5 — Evaluate:

    T1=157.1 lbfT_{1} = 157.1\ \text{lbf}
  6. Step 6 — Check: returning T_1 = 157.1 lbf to

    T1=T2eμβT_1 = T_2 e^{\mu \beta}

    reproduces the given quantities, and both sides carry the same units.

Answer:
T1=157.1 lbfT_{1} = 157.1\ \text{lbf}

Why the other options are there

  • 314.2 — kept a factor of two that cancels in the correct rearrangement.
  • 78.5507 — dropped that same factor in the other direction.
  • 172.8 — rounded an intermediate value before the final step.

Reference: FE Handbook — Statics: Belt Friction

Example 3
Coulomb friction — solve for friction coefficient — Belt Friction (3)

A statics problem uses Coulomb friction. Given normal force (N) = 1,496 lb; friction force (F) = 318.0 lb, determine the friction coefficient (mu).

Given

  • normalforce(N)=1,496lbnormal force (N) = 1,496 lb
  • frictionforce(F)=318.0lbfriction force (F) = 318.0 lb

Find

friction coefficient (mu)

Start with the thinking

  • The governing relation printed in this handbook section is Coulomb friction.
  • Everything except mu is given, so isolate mu symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Statics items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    F=μNF = \mu N
  2. Step 2 — Rearrange the relation so that mu stands alone on the left-hand side.

  3. Step 3

    Listthegivens:normalforce(N)=1,496lb,frictionforce(F)=318.0lbList the givens: normal force (N) = 1,496 lb, friction force (F) = 318.0 lb
  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    μ=0.2126\mu = 0.2126
  6. Step 6 — Check: returning mu = 0.2126 to

    F=μNF = \mu N

    reproduces the given quantities, and both sides carry the same units.

Answer:
μ=0.2126\mu = 0.2126

Why the other options are there

  • 0.4251 — kept a factor of two that cancels in the correct rearrangement.
  • 0.1063 — dropped that same factor in the other direction.
  • 0.2338 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Statics → Belt Friction

Example 4
Belt friction — solve for slack side tension — Belt Friction (4)

A conveyor belt's drive pulley is checked against belt friction slip criteria. Given coefficient of friction (mu) = 0.1300; wrap angle (beta) = 3.8000 rad; tight side tension (T_1) = 1,785 lbf, determine the slack side tension (T_2) in lbf.

Given

  • coefficientoffriction(mu)=0.1300coefficient of friction (mu) = 0.1300
  • wrapangle(beta)=3.8000radwrap angle (beta) = 3.8000 rad
  • tightsidetension(T1)=1,785lbftight side tension (T_1) = 1,785 lbf

Find

slack side tension (T_2), in lbf

Start with the thinking

  • The governing relation printed in this handbook section is Belt friction.
  • Everything except T_2 is given, so isolate T_2 symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Belt friction relates the tight-side and slack-side tensions across a pulley through the coefficient of friction and wrap angle.
T_1T_2Pulley

Figure 4 — schematic for Belt friction — solve for slack side tension — Belt Friction (4)

Step-by-step solution

  1. Step 1 — State the governing relation:

    T1=T2eμβT_1 = T_2 e^{\mu \beta}
  2. Step 2 — Rearrange symbolically for T_2:

    T2=T1eμβT_{2} = \dfrac{T_1}{e^{\mu\beta}}
  3. Step 3 — List the givens: coefficient of friction (mu) = 0.1300, wrap angle (beta) = 3.8000 rad, tight side tension (T_1) = 1,785 lbf.

  4. Step 4 — Substitute the given values:

    T2=T1e0.13003.8000T_{2} = \dfrac{T_1}{e^{0.13003.8000}}
  5. Step 5 — Evaluate:

    T2=1089 lbfT_{2} = 1089\ \text{lbf}
  6. Step 6 — Check: returning T_2 = 1,089 lbf to

    T1=T2eμβT_1 = T_2 e^{\mu \beta}

    reproduces the given quantities, and both sides carry the same units.

Answer:
T2=1089 lbfT_{2} = 1089\ \text{lbf}

Why the other options are there

  • 2,178 — kept a factor of two that cancels in the correct rearrangement.
  • 544.6 — dropped that same factor in the other direction.
  • 1,198 — rounded an intermediate value before the final step.

Reference: FE Handbook — Statics: Belt Friction

Example 5
Coulomb friction — solve for normal force — Belt Friction (5)

A statics problem uses Coulomb friction. Given friction coefficient (mu) = 0.1500; friction force (F) = 367.0 lb, determine the normal force (N) in lb.

Given

  • frictioncoefficient(mu)=0.1500friction coefficient (mu) = 0.1500
  • frictionforce(F)=367.0lbfriction force (F) = 367.0 lb

Find

normal force (N), in lb

Start with the thinking

  • The governing relation printed in this handbook section is Coulomb friction.
  • Everything except N is given, so isolate N symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Statics items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    F=μNF = \mu N
  2. Step 2 — Rearrange the relation so that N stands alone on the left-hand side.

  3. Step 3

    Listthegivens:frictioncoefficient(mu)=0.1500,frictionforce(F)=367.0lbList the givens: friction coefficient (mu) = 0.1500, friction force (F) = 367.0 lb
  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    N=2447 lbN = 2447\ \text{lb}
  6. Step 6 — Check: returning N = 2,447 lb to

    F=μNF = \mu N

    reproduces the given quantities, and both sides carry the same units.

Answer:
N=2447 lbN = 2447\ \text{lb}

Why the other options are there

  • 4,893 — kept a factor of two that cancels in the correct rearrangement.
  • 1,223 — dropped that same factor in the other direction.
  • 2,691 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Statics → Belt Friction

Example 6
Belt friction — solve for coefficient of friction — Belt Friction (6)

A flat belt drive on a pulley must not slip under belt friction limits. Given slack side tension (T_2) = 128.0 lbf; wrap angle (beta) = 2.9000 rad; tight side tension (T_1) = 1,975 lbf, determine the coefficient of friction (mu).

Given

  • slacksidetension(T2)=128.0lbfslack side tension (T_2) = 128.0 lbf
  • wrapangle(beta)=2.9000radwrap angle (beta) = 2.9000 rad
  • tightsidetension(T1)=1,975lbftight side tension (T_1) = 1,975 lbf

Find

coefficient of friction (mu)

Start with the thinking

  • The governing relation printed in this handbook section is Belt friction.
  • Everything except mu is given, so isolate mu symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Belt friction relates the tight-side and slack-side tensions across a pulley through the coefficient of friction and wrap angle.
T_1T_2Pulley

Figure 6 — schematic for Belt friction — solve for coefficient of friction — Belt Friction (6)

Step-by-step solution

  1. Step 1 — State the governing relation:

    T1=T2eμβT_1 = T_2 e^{\mu \beta}
  2. Step 2 — Rearrange symbolically for mu:

    μ=ln⁡(T1/T2)β\mu = \dfrac{\ln(T_1/T_2)}{\beta}
  3. Step 3 — List the givens: slack side tension (T_2) = 128.0 lbf, wrap angle (beta) = 2.9000 rad, tight side tension (T_1) = 1,975 lbf.

  4. Step 4 — Substitute the given values:

    μ=ln⁡(T1/T2)2.9000\mu = \dfrac{\ln(T_1/T_2)}{2.9000}
  5. Step 5 — Evaluate:

    μ=0.9435\mu = 0.9435
  6. Step 6 — Check: returning mu = 0.9435 to

    T1=T2eμβT_1 = T_2 e^{\mu \beta}

    reproduces the given quantities, and both sides carry the same units.

Answer:
μ=0.9435\mu = 0.9435

Why the other options are there

  • 1.8871 — kept a factor of two that cancels in the correct rearrangement.
  • 0.4718 — dropped that same factor in the other direction.
  • 1.0379 — rounded an intermediate value before the final step.

Reference: FE Handbook — Statics: Belt Friction

Example 7
Coulomb friction — solve for friction force (case 2) — Belt Friction (7)

A statics problem uses Coulomb friction. Given friction coefficient (mu) = 0.2700; normal force (N) = 1,570 lb, determine the friction force (F) in lb.

Given

  • frictioncoefficient(mu)=0.2700friction coefficient (mu) = 0.2700
  • normalforce(N)=1,570lbnormal force (N) = 1,570 lb

Find

friction force (F), in lb

Start with the thinking

  • The governing relation printed in this handbook section is Coulomb friction.
  • Everything except F is given, so isolate F symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Statics items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    F=μNF = \mu N
  2. Step 2 — Rearrange the relation so that F stands alone on the left-hand side.

  3. Step 3

    Listthegivens:frictioncoefficient(mu)=0.2700,normalforce(N)=1,570lbList the givens: friction coefficient (mu) = 0.2700, normal force (N) = 1,570 lb
  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    F=423.9 lbF = 423.9\ \text{lb}
  6. Step 6 — Check: returning F = 423.9 lb to

    F=μNF = \mu N

    reproduces the given quantities, and both sides carry the same units.

Answer:
F=423.9 lbF = 423.9\ \text{lb}

Why the other options are there

  • 847.8 — kept a factor of two that cancels in the correct rearrangement.
  • 212.0 — dropped that same factor in the other direction.
  • 466.3 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Statics → Belt Friction

Example 8
Belt friction — solve for tight side tension (case 2) — Belt Friction (8)

A rope wrapped around a capstan uses belt friction to hold a load. Given slack side tension (T_2) = 68.0000 lbf; coefficient of friction (mu) = 0.4300; wrap angle (beta) = 2.9500 rad, determine the tight side tension (T_1) in lbf.

Given

  • slacksidetension(T2)=68.0000lbfslack side tension (T_2) = 68.0000 lbf
  • coefficientoffriction(mu)=0.4300coefficient of friction (mu) = 0.4300
  • wrapangle(beta)=2.9500radwrap angle (beta) = 2.9500 rad

Find

tight side tension (T_1), in lbf

Start with the thinking

  • The governing relation printed in this handbook section is Belt friction.
  • Everything except T_1 is given, so isolate T_1 symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Belt friction relates the tight-side and slack-side tensions across a pulley through the coefficient of friction and wrap angle.
T_1T_2Pulley

Figure 8 — schematic for Belt friction — solve for tight side tension (case 2) — Belt Friction (8)

Step-by-step solution

  1. Step 1 — State the governing relation:

    T1=T2eμβT_1 = T_2 e^{\mu \beta}
  2. Step 2 — Rearrange symbolically for T_1:

    T1=T2eμβT_{1} = T_2 e^{\mu \beta}
  3. Step 3 — List the givens: slack side tension (T_2) = 68.0000 lbf, coefficient of friction (mu) = 0.4300, wrap angle (beta) = 2.9500 rad.

  4. Step 4 — Substitute the given values:

    T1=T2e0.43002.9500T_{1} = T_2 e^{0.4300 2.9500}
  5. Step 5 — Evaluate:

    T1=241.8 lbfT_{1} = 241.8\ \text{lbf}
  6. Step 6 — Check: returning T_1 = 241.8 lbf to

    T1=T2eμβT_1 = T_2 e^{\mu \beta}

    reproduces the given quantities, and both sides carry the same units.

Answer:
T1=241.8 lbfT_{1} = 241.8\ \text{lbf}

Why the other options are there

  • 483.6 — kept a factor of two that cancels in the correct rearrangement.
  • 120.9 — dropped that same factor in the other direction.
  • 266.0 — rounded an intermediate value before the final step.

Reference: FE Handbook — Statics: Belt Friction

Example 9
Coulomb friction — solve for friction coefficient (case 2) — Belt Friction (9)

A statics problem uses Coulomb friction. Given normal force (N) = 922.0 lb; friction force (F) = 1,123 lb, determine the friction coefficient (mu).

Given

  • normalforce(N)=922.0lbnormal force (N) = 922.0 lb
  • frictionforce(F)=1,123lbfriction force (F) = 1,123 lb

Find

friction coefficient (mu)

Start with the thinking

  • The governing relation printed in this handbook section is Coulomb friction.
  • Everything except mu is given, so isolate mu symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Statics items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    F=μNF = \mu N
  2. Step 2 — Rearrange the relation so that mu stands alone on the left-hand side.

  3. Step 3

    Listthegivens:normalforce(N)=922.0lb,frictionforce(F)=1,123lbList the givens: normal force (N) = 922.0 lb, friction force (F) = 1,123 lb
  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    μ=1.2180\mu = 1.2180
  6. Step 6 — Check: returning mu = 1.2180 to

    F=μNF = \mu N

    reproduces the given quantities, and both sides carry the same units.

Answer:
μ=1.2180\mu = 1.2180

Why the other options are there

  • 2.4360 — kept a factor of two that cancels in the correct rearrangement.
  • 0.6090 — dropped that same factor in the other direction.
  • 1.3398 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Statics → Belt Friction

Example 10
Belt friction — solve for slack side tension (case 2) — Belt Friction (10)

A conveyor belt's drive pulley is checked against belt friction slip criteria. Given coefficient of friction (mu) = 0.1700; wrap angle (beta) = 0.6000 rad; tight side tension (T_1) = 1,448 lbf, determine the slack side tension (T_2) in lbf.

Given

  • coefficientoffriction(mu)=0.1700coefficient of friction (mu) = 0.1700
  • wrapangle(beta)=0.6000radwrap angle (beta) = 0.6000 rad
  • tightsidetension(T1)=1,448lbftight side tension (T_1) = 1,448 lbf

Find

slack side tension (T_2), in lbf

Start with the thinking

  • The governing relation printed in this handbook section is Belt friction.
  • Everything except T_2 is given, so isolate T_2 symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Belt friction relates the tight-side and slack-side tensions across a pulley through the coefficient of friction and wrap angle.
T_1T_2Pulley

Figure 10 — schematic for Belt friction — solve for slack side tension (case 2) — Belt Friction (10)

Step-by-step solution

  1. Step 1 — State the governing relation:

    T1=T2eμβT_1 = T_2 e^{\mu \beta}
  2. Step 2 — Rearrange symbolically for T_2:

    T2=T1eμβT_{2} = \dfrac{T_1}{e^{\mu\beta}}
  3. Step 3 — List the givens: coefficient of friction (mu) = 0.1700, wrap angle (beta) = 0.6000 rad, tight side tension (T_1) = 1,448 lbf.

  4. Step 4 — Substitute the given values:

    T2=T1e0.17000.6000T_{2} = \dfrac{T_1}{e^{0.17000.6000}}
  5. Step 5 — Evaluate:

    T2=1308 lbfT_{2} = 1308\ \text{lbf}
  6. Step 6 — Check: returning T_2 = 1,308 lbf to

    T1=T2eμβT_1 = T_2 e^{\mu \beta}

    reproduces the given quantities, and both sides carry the same units.

Answer:
T2=1308 lbfT_{2} = 1308\ \text{lbf}

Why the other options are there

  • 2,615 — kept a factor of two that cancels in the correct rearrangement.
  • 653.8 — dropped that same factor in the other direction.
  • 1,438 — rounded an intermediate value before the final step.

Reference: FE Handbook — Statics: Belt Friction

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