Sinking and Floating!
Buoyancy: The Science of Why Objects Float or Sink
Buoyancy is an incredibly important part of the natural world. Buoyancy affects all objects in the water, from HUGE cruise and cargo ships, all the way down to the smallest duckling.
In this experiment, your child will predict and observe which of the household items you have collected will sink and float. Consider the following properties when making your hypotheses:
How HEAVY is the object? The heavier the object is, the more likely it is to sink!
How BIG is the object? Larger objects tend to displace more water, an important factor for an object’s buoyancy.
Is this object POROUS? Objects that contain pockets of air such as sponges, wood tend to float because air is so light!
Suggested Materials:
Tub with water
Rubber Duck
Egg
Tin foil
Sponge
Pencil
Bottle Cap
Salt
Directions:
Fill a tub with water
Place an object in the middle of the tub and observe whether the object sinks or floats.
Separate the objects by whether they sink or float.
Record your observations!
Examining the Experiment: Breaking Down Buoyancy
Buoyancy is the upward force exerted by a fluid. There are two main types of buoyancy:
Positive Buoyancy- this occurs when the density of the object is lighter than the density of the liquid it is placed in. When this happens, the object will FLOAT.
Negative Buoyancy- this occurs when the density of the object is heavier than the liquid it is placed in. When this happens, the object will SINK.
Science Extension: Water Density and Buoyancy
Did you know that water density affects whether an object will sink or float? When water has a high density that means there are a lot of molecules packed tightly together. When it has a low density, that means the molecules are fewer and looser. You can increase the density of your water by adding salt. Increasing the density of your water might mean that some of the objects you just tested might be lighter than the water now. Re-test your objects to see if any of the objects that sank, now float!
