Weight is a concept that can be explored easily as you and your child go about the routine tasks of the day. If your child goes with you to the supermarket try turning the trip into an opportunity to learn about heavy and light, and all the variations in between.
This is also a chance to introduce mathematical language as you use words like heavier, heaviest, lighter, and lightest. It's easy to do this, by simply asking your child to pick the things off the shelf as you select them, asking questions like "Does the bag of potatoes feel heavy or light?" "What about the lettuce?"
As your child gets practice with this game, start to make comparisons between different objects: "Is the cucumber heavier or lighter than the grapefruit?"
The supermarket is also a great place to introduce your child to the concept of a scale, since she can see the needle move up as she places more things in. Make comparisons to other scales she may have seen, like a bathroom scale. Don't forget to thank her for all the help with shopping!