Example of Negative Work Done on an Object

Introduction: In physics, work done on an object is defined as the energy transferred to or from the object by means of a force acting on it. When the force and the displacement are in the same direction, work done is considered positive, whereas when they are in opposite directions, work done is negative.

Example: Lifting an Object Upwards:

• Scenario: Imagine lifting a box off the ground to place it on a shelf.
• Force and Displacement: In this scenario, the force exerted by the person is upwards, while the displacement of the box is also upwards.
• Direction of Work: Since the force and displacement are in the same direction (upwards), the work done on the box is positive.
• Magnitude of Work: The magnitude of the work done is determined by the force exerted and the distance over which it is applied.

Example: Lowering an Object Downwards:

• Scenario: Now, consider lowering the same box back to the ground from the shelf.
• Force and Displacement: Here, the force exerted by the person is still upwards, but the displacement of the box is downwards.
• Direction of Work: The force and displacement are in opposite directions, with the force opposing the displacement.
• Negative Work: As a result, the work done on the box is negative because the force exerted by the person is against the direction of motion.
• Magnitude of Work: The magnitude of the work done is still determined by the force exerted and the distance over which it is applied, but with a negative sign to indicate the direction.

Conclusion: In conclusion, when an object is moved in a direction opposite to the force applied, the work done on the object is negative. This concept is crucial in understanding the transfer of energy and the behavior of objects under the influence of forces.

Understanding Work Done on an Object

Introduction: In the realm of physics, the concept of work done on an object holds significant importance. Work is defined as the force applied to an object over a distance, causing it to move. However, there are instances where the work done on an object is zero. Let's explore one such example.

Example: Work Done on a Stationary Object

Scenario: Consider a book resting on a table. You exert a force by pressing down on the book with your hand, but the book doesn't move.

Explanation: In this scenario, despite applying a force to the book, there is no displacement in the direction of the force. Therefore, the work done on the book is zero.

Factors Contributing to Zero Work:

• No Displacement: The book remains stationary; hence, there is no displacement along the direction of the force.
• Perpendicular Force: If the force you apply is perpendicular to the direction of potential motion, no work is done. In this case, the force of gravity pulling the book downward is balanced by the normal force exerted by the table upward, resulting in zero net force in the direction of motion.
• Magnitude of Force: Even if you apply a significant force, if it doesn't result in any displacement in the direction of the force, the work done is zero.

Conclusion: Understanding the conditions under which work done on an object is zero is crucial in grasping the concept of work in physics. In scenarios where there is no displacement or the force is perpendicular to the direction of potential motion, the work done on the object is zero.