IGCSE Physics - 1.7.2 Work

This section covers the concept of work in physics, focusing on the definition, the formula for calculating work done, and its relationship with energy transfer.

Definition of Work

In physics, work is defined as the transfer of energy that occurs when a force causes displacement of an object. It's not simply about applying a force; the force must actually cause movement.

The Equation for Work

The work done (W) by a constant force (F) over a distance (d) is given by the following equation:

$$W = F \times d$$

Where:

• W is the work done, measured in Joules (J).
• F is the magnitude of the force applied, measured in Newtons (N).
• d is the distance over which the force acts, measured in meters (m).

This equation assumes the force is applied in the same direction as the displacement. If the force and displacement are at an angle to each other, the calculation becomes more complex (see the next section).

Work and Change in Energy

Work done is directly related to the change in energy of an object. The work done on an object is equal to the change in its energy. This can be expressed as:

$$W = \Delta E$$

Where:

• W is the work done (in Joules).
• ΔE is the change in energy (in Joules). This could be a change in kinetic energy, potential energy, or other forms of energy.

For example, if work is done on an object, its energy increases. If work is done by an object, its energy decreases.

Work done at an angle

If the force is not applied in the same direction as the displacement, we need to consider the component of the force that is in the direction of the displacement. The work done is then:

$$W = F \times d \times \cos{\theta}$$

Where:

• θ is the angle between the force vector and the displacement vector.

If the force is in the same direction as the displacement, then θ = 0° and cos(0°) = 1, so the equation simplifies to the basic work equation: W = Fd.

Example Calculation

A student pushes a box with a force of 20 N over a distance of 5 meters. Calculate the work done by the student.

Using the equation W = Fd:

W = 20 N × 5 m = 100 J

Therefore, the student does 100 Joules of work.

Quantity	Symbol	Units
Work Done	W	Joules (J)
Force	F	Newtons (N)
Displacement	d	Meters (m)
Change in Energy	ΔE	Joules (J)

Understanding work is fundamental to understanding energy transfer in physics. It allows us to quantify how energy is moved from one form to another.