What explains the result?
Dissolved salt raises water density, increasing buoyant support on the egg.
PHYSICAL SCIENCE · GRADES 4–8
Salt-water buoyancy
INVESTIGATION QUESTIONAt what salt level does the egg begin to float?
● ILLUSTRATIVE SCIENCE MODEL
ENGLISH CAPTIONS
Prepare equal water volumes. Only solution salinity should differ across the jars.
0.0 / 3.0 s
Where does this matter?
Salinity affects lake and ocean buoyancy and helps explain why people float differently in water bodies.
What should you keep in mind?
Egg age and shape vary. The model uses typical values and cannot determine whether food is safe to eat.
SALINITY · DENSITY · BUOYANT FORCE · GRADES 4–8
Make an
egg float
Increase salt concentration in a clear column and observe how the egg’s resting height changes as the liquid becomes denser.
SALINITY COLUMN · CROSS-SECTIONFRESH WATER
surfacebottom
FRESH WATEREGG RESTING HEIGHT
LIQUID DENSITY0.998 g/mLrelative model
Water + dissolved salt Egg rests where buoyancy balances weight
DENSITY & BUOYANCY NOTES
Explain what you observe
1Fresh water0 g/L illustrative condition · density 0.998 g/mL
2Lightly salted35 g/L illustrative condition · density 1.020 g/mL
3Very salty290 g/L illustrative condition · density 1.190 g/mL
Salt increases water’s mass per volume when it dissolves. Buoyant force equals the weight of displaced liquid, so denser water can support the same egg with less displaced volume. At an intermediate density an egg may hover; with still denser water it rises toward the surface.
In the real world: Ocean salinity contributes to seawater density and circulation; high-salinity water masses can sink beneath less-dense water and influence ocean mixing. A kitchen jar is a simple model, not a scale model of ocean currents.