Torque

Torque creates rotational acceleration when a force is applied to a lever.  Follow examples on this StickMan Physics page.

Clockwise Counterclockwise

Torque (τ) is the rotational equivalent of force and creates a rotational acceleration. Therefore torque occurs around a fulcrum or pivot point which is the center of rotation.  A triangle can represent the fulcrum with a rotation either clockwise (CW) or counterclockwise (CCW).  Clockwise is the direction a clocks handle rotates and can be seen in the picture.

Torque occurs when you apply a force with a perpendicular component to a lever or length away from a rotating point.  See torque equation variables and standard units below.

Clockwise Clock

Torque Variables

Name Variable Unit Unit Abbreviation
Torque Ƭ Newton times meter N∙m
Perpendicular Force F Newton N
Distance d Meters m

Torque Equation (τ =Fd)

Torque increases as distance away from the fulcrum a perpendicular force is applied.  It also increased when the force itself increases.  So perpendicular force and distance directly relate to torque.  Therefore, an increase either perpendicular force or distance torque, keeping everything else the same, torque would go up.

increasing torque

Example Problems:

1. How much torque do you create with a 100 N perpendicular force placed 0.45 meters from the fulcrum?

Torque
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2. How much force would Joe have to apply perpendicular to create 550 Nm of torque 0.20 meters away from the bolt he is trying to loosen?

Torque2
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Perpendicular Force Gives the Most Torque and Parallel None

Any force other than one applied parallel can have a perpendicular component seen by the red arrow in the animation.  The blue arrow is the actual force applied and the green arrow is the wasted parallel component of force that does not create torque.  Torque decreases as force at an angle away from the perpendicular direction increases.  90 degrees is the furthest away from the perpendicular and would be parallel.  Therefore, you produce no torque when force is parallel.

Maximum Torque

Example Problems:

3. What torque results from a 250 N force 30° from perpendicular on a wrench 0.28 meters away from the bolt?

torque3 picture

Torque 3
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Multiple Torques

You add multiple torques after accounting for direction.  Any clockwise force will be positive mathematically and counterclockwise negative.

Balanced Systems

When you have a balanced system, for example, two kids on a teeter-totter, the sum of the forces is equal to zero.  You can rewrite the equation with all of the counterclockwise (CCW) forces written on the left of the equals and all the clockwise forces written on the right.  Since all the counterclockwise forces will be negative on the right side of the equation, they will be positive when added to both sides.  The result is the bottom balanced torques equation (… + F1d1= F2d2 + …).  When more torques are in a system, you add them to their corresponding clockwise or counterclockwise side and renumber.

 

Torque Equations

Standard Balancing Torques Equation

In the picture, there are two stickmen on a teeter-totter.  The blue stickman on the left creates a counterclockwise (CCW) rotation and the red on the right creates a clockwise (CW) one.    They balance each other (zero sum of torques) resulting in the equation below them (F1d1 = F2d2).  If there was an additional person on the left (counterclockwise torque) this would become (F1d1 + F2 d2 = F3d3).  If there was an additional person on the right "instead" it would become (F1 d1 = F2d2 + F3d3).  The … in the equations above mean you add as many individual distances and forces to that rotational side.

Balanced Torques

Example Problem

Sum of Torques

4. What is the sum of all torques in the system above?

Sum of torques solution
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balanced Torque Example

5. Where should you place a 19.6 N weight to balance a 9.8 N weight 0.4 meters on the right?

balanced torques answer
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(Click Here for All the Torque Problems and Solutions)

Torque Practice Quiz

Torque Quiz

Do you know your torque?

increasing torque

Find out by taking this quiz.

1 / 9

What is the term for a pivot point where rotation can occur?

2 / 9

What is the term for the bar or arm attached to a pivot where a rotation can occur?

3 / 9

What happens to torque if you increase the distance a perpendicular force is applied on a lever from a fulcrum?

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What happens to torque if you increase the distance a parallel force is applied on a lever from a fulcrum?

5 / 9

Which would give the most torque if all forces applied at point A, B, C, and D were the same?

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6 / 9

Which would give the least torque if all forces applied at point A, B, C, and D were the same?

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Forces on a Wrench

How much torque would be provided by a 15N force the direction of A above if it was 0.10 meters away from the bolt?

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How far away should a 0.50 kg mass be placed on the left side of a fulcrum to balance a 2.0 kg mass 0.50 m on the right side of a fulcrum?

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How far away should you place a 0.50 kg mass on the left side of a fulcrum to balance a 0.50 kg mass 0.10 meters and another 2.0 kg mass 0.50 m both on the right side of a fulcrum?

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