Buoyancy: How can a ship made of iron that weighs about 200 million pounds float?

FOIL SHAPE PREDICTION OBSERVATION EXPLANATION

Boat Sink or Float Sink or Float

Ball Sink or Float Sink or Float

Block Sink or Float Sink or Float

Aluminum Foil Boats

• Objective: To design/build two different aluminum foil boats that will hold as many pennies as possible without sinking.

• Procedure1. Obtain two 20cmx20cm pieces of aluminum foil. 2. Build your boats.3. Test them by adding pennies until they sink.4. Dry the pennies off and return them.5. Which boat in the class won? Why?

Shape and density determine if something will float.

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Buoyant Force: When an object displaces water the water pushes back on it.

What happens to the weight of an object when placed in water?

Intro to Forces: PHET Sim

• Force: a push or a pull (unit: Newtons)

• If Force are balanced an object will not move or change its motion!

• Unbalanced forces lead to changes in motion.

https://phet.colorado.edu/en/simulation/forces-and-motion-basics

Buoyant Force (upward push of water)

Weight Force (heaviness of object)

1. If Weight is greater than Buoyant Force an object sinks.

2. If Buoyant Force is greater than weight the object rises and then floats.

3. When Buoyant Force equals weight the object floats or suspends.

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Which is greater: the Weight or Buoyant Force?

Floating: Buoyant Force = Weight

F = 100N

F = 100N

If a 100N boat is floating the water must be pushing on it

with a force of 100N

If we add weight (50N) to the boat it will sink down deeper and the

buoyant force will increase.

F = 150N

F = 150N

Buoyant Force (upward push of water)

Weight Force (heaviness of object)

Archimedes Principle: Buoyant force is equal to the weight of the liquid displaced .

The more water an object displaces the more buoyant force pushing on it.

This is why a block of aluminum sinks but an aluminum foil boat floats.

Shape is important!

If you were to hold a basketball under water it will push back very

hard and would fly upwards if your were to release it.

Buoyant Force > Weight

If you were to hold a basketball under water it will push back very

hard and would fly upwards if your were to release it.

Buoyant Force > Weight

When floating the buoyant force on ball

equals its weight.

Why is it easier to lift a person in water?

50N

50N

Weight (force)

Lift (force)

Why is it easier to lift a person in water?

50N

50N

Weight (force)

Lift (force)

Weight (force)

Lift (force)Buoyant (force)

The water helps you!

Concrete Boats

• Heavy iron ships can float because they are shaped to displace a large amount of water and being hollow and filled with air reduces their overall density.

• Its easier to pick someone up in water because the water helps you (buoyant force).