Weight & Density

Weight and density are measures used to describe physical properties of materials and objects. Weight refers to the force due to gravity on an object, commonly reported in kilograms or pounds. Density measures how much mass is contained in a given volume and helps predict whether an object will float or sink and how heavy it feels relative to its size.

• Weight = force (depends on gravity) — common units: kg, lb.
• Mass = amount of matter (often measured in kg) — not the same as weight.
• Density = mass / volume — common units: kg/m³, g/cm³.
• Density helps compare materials (e.g., aluminum vs steel) and is crucial for shipping, packaging, and materials selection.

Keep the concepts separate and use correct units:

• Mass is constant and measured in kilograms (kg).
• Weight is a force (mass × gravity) and often given in newtons (N) or informally in kg/lb on scales.
• Density = mass / volume. Use kg/m³ or g/cm³ for solids and liquids.

In many business contexts (shipping), 'weight' on documents means mass measured on a scale; clarify units when needed.

Learners often make predictable errors when using weight and density vocabulary. Watch for these:

• Confusing mass and weight — mass is not affected by gravity changes; weight is.
• Using incorrect units or mixing units (e.g., kg with mL without conversion).
• Forgetting to include or exclude packaging (gross vs net weight).
• Using 'weight' as a verb incorrectly (e.g., 'The box weights 10 kg' is wrong).
• Mistaking density for weight when comparing how heavy objects feel relative to size.

Always check the required unit, clarify if packaging is included, and use correct verb/noun forms.