Table of Contents
What is Work?
Consider a guy doing certain activities like washing dishes, writing a letter and brushing his teeth. Now, it is quite interesting to note that in terms of physics all these activities are not considered as work.
Work, in physics, measures the energy transfer that occurs when an object is moved over a distance by an external force at least part of which is applied in the direction of the displacement.
There are certain conditions that are required to be fulfilled for a work to be done.
What are the necessary conditions for work to be done?
There are 2 requirements that should be met for work to be done:
- A force needs to be applied on the object.
- The object needs to be displaced.
The direction of application of force and direction of displacement of the object plays a very important part in calculating work done.
The formula to calculate work is
Work (W) = Force (F) × Displacement (d) × cos θ
Where:
Work (W) is measured in joules (J), which is the unit of energy.
Force (F) is the magnitude of the force applied to the object, measured in Newton (N).
Distance (d) is the displacement of the object caused by the force, measured in meters (m).
θ is the angle between the direction of the force and the direction of the displacement. The cosine of this angle is used to account for any component of the force that is not aligned with the displacement.
It’s important to note that this formula assumes that the force and the displacement are in the same direction. If the force is applied at an angle to the displacement, only the component of the force that is in the same direction as the displacement contributes to the work done.
If the displacement is in the direction of force θ is 0o, and hence cosθ will be 1. Therefore, the formula of work can be given as:
Work (W) = Force (F) × Distance (d)
Unit of work
The unit of work is the joule (J). The joule is derived from basic SI units, representing the amount of energy transferred when a force of one newton is applied to an object and displaces it by one meter in the direction of the force.
1 J= 1N.m
Positive and Negative Work
Work can be positive or negative, depending on the angle between the force and the displacement. When the force and displacement are in the same direction, the work is positive, indicating that energy is being transferred to the object. On the other hand, if the force and displacement are in opposite directions, the work is negative, indicating that energy is being taken away from the object.
Is Work a scalar quantity or a vector quantity?
Work is a physical quantity that has magnitude but no direction. Thus, work is a scalar quantity.
Solved examples on Work Formula
Example 1: Suppose you exert a vertical force of 50N to lift a box vertically upward by a distance of 2 meters. Assuming there is no angle between the force and displacement find the work done on the box.
Solution: Since the displacement is in the direction of the applied force, we can write the formula for work as:
Work (W) = Force (F) × Displacement (d)
W = 50 N × 2 m ×
W = 100 J
Therefore, work done on the box will be 100 J.
Example 2: A weight of 500 newtons is lifted using a pulley system. The pulley is attached to a rope that is pulled over a distance of 10 meters with a force of 100 newtons. Calculate the work done.
Solution:
In this scenario, the force and displacement are not in the same direction, so we need to find the component of the force acting in the direction of the displacement. This can be done using the following equation:
cos θ = force in direction of displacement / applied force
Force in direction of displacement = applied force × cos θ
Since the angle between the force and displacement is not given, we assume it is 180 degrees (opposite direction). Thus, cos 180° = -1, and the force in the direction of the displacement is:
Force in direction of displacement = 100 N × (-1)
Force in direction of displacement = -100 N
Now we can calculate the work done using the formula:
Work (W) = Force (F) × Distance (d) × cosθ
W = (-100 N) × 10 m × cos 180°
W = (-1000 J)
The negative sign indicates that the work done is negative, which means that work is done against the gravitational force on the weight, resulting in a decrease in potential energy. Therefore, the work done in this case is 1000 joules in the opposite direction of the applied force.
Frequently asked questions on Work Formula
What is work in physics?
Work in physics refers to the transfer of energy that occurs when a force is applied to an object, causing it to move a certain distance in the direction of the force. It is a measure of the amount of energy transferred or expended in performing a task.
What is the unit of work?
The unit of work is the joule (J). It represents the amount of energy transferred when a force of one newton is applied to an object and displaces it by one meter in the direction of the force.
How is work calculated?
Work is calculated using the formula: Work (W) = Force (F) × Distance (d) × cosθ, where F is the magnitude of the force applied, d is the displacement of the object, and θ is the angle between the force and displacement vectors. The cosine of the angle accounts for any component of the force not aligned with the displacement.
What is the difference between work and power?
Work and power are related but distinct concepts. Work measures the amount of energy transferred or expended in performing a task, while power represents the rate at which work is done or energy is transferred. Power is calculated by dividing the amount of work done by the time taken to do it.
Can work be negative?
Yes, work can be negative. When the force and displacement are in opposite directions, the work done is negative, indicating that energy is being taken away from the object or system. Conversely, when the force and displacement are in the same direction, the work is positive, indicating energy transfer to the object or system.
What are some examples of work in everyday life?
There are numerous examples of work in everyday life, such as lifting objects, pushing a car, climbing stairs, or even walking. Any activity that involves applying a force to move an object or exerting effort over a distance requires work to be done.
Can work be zero?
Yes, work can be zero. Work is zero when there is no displacement occurring despite the presence of a force or when the force and displacement vectors are perpendicular to each other. In these cases, although a force may be applied, there is no movement along the direction of the force.
Is work a scalar or vector quantity?
Work is a scalar quantity since it only has magnitude and no specific direction. However, it is important to note that the force and displacement vectors involved in calculating work are vector quantities.
