Density
Density is how tightly packed the stuff inside something is.
A bowling ball and a basketball are about the same size. Pick them both up — the bowling ball is way heavier. Same size, more stuff packed in. That is higher density.
In your experiment...
When you drop a raisin in fizzy water, it sinks because the raisin is denser than the liquid. Gas bubbles stick to its surface, making it float back up. At the top, the bubbles pop, and the raisin sinks again.
Projects that explore density
Explaining density by grade level
K–2nd grade
Heavy things can be small. Light things can be big. A rock is small but heavy. When something is packed tight, we say it has high density.
3rd–5th grade
Density means how much mass fits in a certain volume. A golf ball and a ping-pong ball are the same size, but the golf ball has more mass packed in — higher density.
6th–8th grade
Density is the ratio of mass to volume: d = m / v. Units are typically g/cm³ or kg/m³. Temperature affects density — warm water is less dense than cold water.
High school
Density is an intensive property — it does not depend on the amount of substance. It connects to buoyancy through Archimedes principle.