Which of the following is an example of a couple?

Analysis

A couple in physics is defined as a pair of forces that are equal in magnitude, opposite in direction, and act along parallel lines but not along the same straight line. The primary effect of a couple is to produce a turning effect (torque) without causing any linear acceleration.

Concept Explanation

To identify a couple, look for these three conditions:

1. Two forces: There must be two distinct forces acting on the object.
2. Equal and Opposite: The forces must be equal in magnitude and act in opposite directions.
3. Turning Effect: The forces must be applied at different points to create a rotation around a central pivot or axis.

Let's evaluate the examples provided:

• Screwdriver: When you twist a screwdriver, your thumb and fingers exert two equal forces in opposite directions on opposite sides of the handle to create rotation. This is a classic example of a couple.
• Cross Wrench: When loosening lug nuts, you push down on one arm of the wrench and pull up on the opposite arm. These two forces are equal, opposite, and parallel, creating a couple.
• Steering Wheel: When turning a steering wheel, your hands are placed on opposite sides of the wheel, applying equal and opposite forces to rotate it. This is also a couple.

Solution

Since the screwdriver, the cross wrench, and the steering wheel all involve two equal, opposite, and parallel forces acting to produce a turning effect, they all qualify as examples of a couple. Therefore, "All of the above" is the correct classification.

Identification of the Answer

The correct option is A.

Exam Tip

Whenever you see a question about a "couple," think of rotation. If the action involves using two hands or two points of force to turn an object (like a tap, a steering wheel, or a wrench), you are dealing with a couple!