Some things float and some sink — Physical education, 4–6 years
Test objects in water and notice that size, shape and material can all affect what happens.
Float or sink?
An object floats when it stays at the water’s surface, and it sinks when it goes down. A large object can float, while a small one can sink. The material and the shape matter, not just how big or heavy the object looks.
Why do we compare them?
People needed boats, buckets and containers that would stay on water instead of sinking. Watching what floats and what sinks gave them a useful way to choose materials and shapes. The same simple test helps us make a prediction before placing something in water.
Make a foil boat
Scrunch a small square of foil into a tight ball and place it in water; it sinks. Take another square, shape it like a wide little boat, and place it gently on the water; it floats. Add coins one at a time until the sides dip low and water enters, then it sinks.
Big does not always mean sink
It is reasonable to think a big object must sink, because a large stone does. But a wide, hollow shape can spread its weight over more water and stay up. That is why a huge steel ship can float, while a small steel nail sinks.
Where does floating help?
Boats float so people and goods can travel across rivers, lakes and seas. Life jackets and some rescue rings float to help keep a person at the surface. Fish use their bodies and special air spaces to stay at different depths in water.
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