A strong correlation exists between weight and gravity. The weight of an object is determined by its mass relative to that of another object. The weight of air and water is affected by objects placed in containers with just air and water. To conduct an experiment that demonstrates the relative weight of objects in air and water, place a bucket of water on a scale, followed by an empty bucket. After recording both weights, place an object in the empty bucket, and then place it in the bucket with water. The bucket with water will experience a smaller weight increase, thus demonstrating that water absorbs more of an object's weight than does air.
Water and air can be measured on a scale using balloons. To prove this, fill one balloon with air and another with water, and attach both to a scale. Observe which one pulls up the scale and which one is pushed down. The one that pulls up the scale weighs more (normally, the object that pushes its side of the scale down weighs more, but since balloons pull upward, the one that pulls its side up more weighs more).
One indicator of weight is mass. Mass is the amount of matter in an object. Weight is determined by mass, since all matter has weight, and there is no weight without matter. You can determine whether water or air has more mass per square inch by filling balloons up with either substance until they pop. The balloon that's bigger when it pops has less mass per square inch, since each square inch of mass has exerted less pressure on the balloon.
It's relatively easy to change the state of water/ice (h2o), since it has a relatively high freezing point and a relatively low boiling point. In one experiment, you compare the weight of liquid/frozen h2o to the weight of air, and record any differences you notice. Fill the balloon with water from a tap by putting the hole over the tap. Pour this water out into a bowl after weighing the balloon, leave the bowl in the freezer, then take it out when the water has turned to ice. Then, break the ice down into small pieces by putting it in a plastic bag and dropping the bag on a hard surface (e.g., cement). Put the ice particles into the balloon and then weigh the balloon. Weigh the air balloon by attaching it to a two-sided scale with a piece of string.