Skill: Choose appropriate units of mass

Mass tells how heavy an object is.

• Use grams (g) for lighter objects, such as a pencil, an apple, or a paper clip.
• Use kilograms (kg) for heavier objects, such as a backpack, a dog, or a bicycle.

Choose the unit that gives a sensible number.

Example: A full school backpack has a mass of $4\ \square$.

1. A backpack is fairly heavy, so kilograms are more suitable than grams.
2. Test the choices:
   • $4$ grams would be far too light for a full backpack.
   • $4$ kilograms sounds sensible.
3. Write the correct unit:

$$\boxed{4\text{ kg}}$$

So, a full school backpack has a mass of about $4$ kilograms. Remember, the same mass is shown by a larger number when using grams: $1$ kilogram is $1{,}000$ grams.