A movement along the labour supply curve happens only when the wage rate changes. This change leads to a different quantity of labour supplied. It is important to note that this movement is caused only by wage changes, not by other external factors.

The movement works in two ways:

• When the wage rises, workers provide more labour, leading to an extension along the curve. This happens because more people choose to work or current workers choose to work more hours.
• When the wage falls, workers provide less labour, leading to a contraction along the curve.

This concept is different from a shift of the entire supply curve, which happens when factors like population size, immigration, or social changes occur.

The curve slopes upwards because of two main reasons: the substitution effect (higher wages make working more rewarding than leisure time) and the income effect.