Work
Definition of work, its SI unit, dimensional formula, and calculation of work done by a constant force.
What is Work?
The energy transferred to or from an object by the application of force along a displacement.
Key formula / rule: Work done by a constant force
Key points
- Define work in physics.
- Calculate work done by a constant force.
- Identify conditions for positive, negative, and zero work.
- State the SI unit and dimensional formula of work.
Common exam trap
Confusing work with force or displacement alone.
Definitions
- Term
Work
- Meaning
The energy transferred to or from an object by the application of force along a displacement.
- Term
Joule (J)
- Meaning
The SI unit of work and energy, defined as the work done when a force of one Newton displaces an object by one meter in the direction of the force.
Learning objectives
Define work in physics.
Calculate work done by a constant force.
Identify conditions for positive, negative, and zero work.
State the SI unit and dimensional formula of work.
Formulae
- Name
Work done by a constant force
- Note
Scalar product of force vector (F) and displacement vector (d).
- Expression
W = F ⋅ d
- Name
Work done by a constant force (magnitude form)
- Note
F is magnitude of force, d is magnitude of displacement, θ is the angle between F and d.
- Expression
W = Fd cos θ
- Name
Work done by gravity
- Note
hi is initial height, hf is final height. Positive if object falls, negative if lifted.
- Expression
Wg = mg(hi - hf)
Prerequisites
Vectors (dot product, angle between vectors)
Force and its types
Displacement
Energy
Common mistakes
Confusing work with force or displacement alone.
Forgetting to consider the angle between force and displacement.
Assuming work is always positive.
Incorrectly calculating the dot product or using vector components.
Using non-SI units without conversion.
Keywords
Work
Force
Displacement
Energy Transfer
Scalar Product
Joule
Angle
Constant Force
Practice preview
What is the SI unit of work?…
easy
A force of 5 N acts on a body and displaces it by 2 m in the direction of the force. Calculate the work done.…
easy
The dimensional formula for work is:…
easy