Mada za sehemu hiiConduct elementary scientific experimentsMada 4
- Conduct simple experiments to identify acids and bases substances in the environment
- Conduct simple experiments about machines
- Conduct simple experiments on floating or sinking
- Conduct experiments on simple electric circuits
Floating and Sinking
When we place an object in water, two forces act on it:
- Weight — the force pulling the object downward (due to gravity)
- Upthrust (buoyant force) — the force pushing the object upward (from the water)
An object floats when the upthrust from the water is strong enough to hold it up. An object sinks when its weight is stronger than the upthrust pushing it up.
A simple way to remember: objects that are light for their size tend to float, while objects that are heavy for their size tend to sink.
- Wood (like a piece of mbata or msasa)
- A balloon filled with air
- A plastic bottle
- A canoe or boat made of wood
- Leaves
- An empty plastic container
- Stones (mawe)
- Metal coins (sarafu)
- Glass
- Keys
- Nails
- A metal spoon
Follow these steps to find out which objects float and which sink:
What You Need
- A clear container or bucket filled with water
- Various objects to test (wood, stone, coin, plastic bottle, leaf, metal key)
- A towel to dry your hands
What To Do
-
Fill a container with clean water until it is about three-quarters full.
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Choose one object to test first.
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Gently place the object on the surface of the water. Do not throw it in forcefully.
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Watch carefully — does the object stay on top of the water, or does it go down?
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Record your result — write "floats" or "sinks" for each object you test.
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Repeat with all your objects.
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Compare your results. Which objects floated? Which sank?
Example Results
| Object | Floats or Sinks? |
|---|---|
| Piece of wood | Floats |
| Stone | Sinks |
| Coin | Sinks |
| Plastic bottle (empty) | Floats |
| Leaf | Floats |
| Metal key | Sinks |
Objects that float are usually less dense than water. They are light for the amount of space they take up. When placed in water, they displace (push aside) enough water to create upward force that holds them up.
Objects that sink are usually denser than water. They are heavy for their size. They push aside only a small amount of water, so the upward force is not strong enough to support them.
A hollow object like a boat can float even if it is made of metal because the air inside makes the whole object less dense than water overall.
In Tanzania, this knowledge is useful when fishing. Traditional fishermen on Lake Victoria use boats made of wood that float because wood is less dense than water. They also know that heavy fishing nets made of metal will sink, so they use floats (buoys) made of plastic or hollow containers to keep their nets floating at the right depth in the water.
Swali
What determines whether an object floats or sinks in water?
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