Floating
and
Sinking
Buoyancy
4.0 Are All Bottles of Air Created Equal?

If the bottle is filled with air before the Demo:

[1] There is ___________ air is in the bottle after the balloon

(more, less)

inflates itself.

[2] The _______ bottle has _______ air in it than the cold.

hot, Cold) (more, less)

[3] When the air is _______ some air ballast must leave to bottle (heated, cooled)

to make the bottle _________ buoyant.

(more, less)

4.11 The Myth of The Impossible Exposed.

Greg's Model Air Balloon

The things thought impossible are never tried. until someone sees the impossible as a possibility.

[1] Why does hot air make the balloon rise?

Draw in density dots to show how the hot inside is different than the cold air outside.

[2] How much lifting power does the balloon have?

(How can you measure it?)

[3] Build your own model air Balloon and improve the lifting power?

4.12 archimedes and Air Balloons

The balloon rises as the air is

heated. When air heats up it expands. Some air

ballast leaves the

balloon. Hot air has less

weight for the same size balloon. The stronger

buoyant force of the

air displaced pushes

the balloon up. The balloon rises as it

gets lighter when the

air inside gets hot.

Answers- "Archimedies and Air Balloons"

The balloon rises as the air is heated. When air heats up it expands. Some air ballast leaves the balloon. Hot air has less weight for the same size balloon. The stronger buoyant force of the air displaced pushes the balloon up. The balloon rises as it gets lighter when the air inside gets hot.

4.13 Container Dunk

Feeling the buoyant force:

You can feel the buoyant force by forcing various size sealed containers into a pail of water..

Arrange the containers from largest to smallest buoyant force.

Conclusion summary.

The buoyant force is stronger when the size is ________ is shaped to displace more water. (larger, smaller)

 
The Strength of the Buoyant Force
Buoyant force (Loss of weight by the cylinder) 

____ N 

0.25N - ___ N = ___ N

Weight of water displaced by the cylinder. 

____ N 

0.25N+ ___ N = ___ N

 
The Strength of the Buoyant Force
Weight of water displaced by the cylinder. 

____ N

Buoyant force = Displaced Water =(Loss of weight by the cylinder)
Play Archimedes. Convince to the skeptic of the strength of the buoyant force by using the following materials.


King Hiero's Crown

Question : If different metal samples have equal weight in air do they also have equal weight in the water?

Hypothesis: If two samples of metal weigh the same in air they _________________________________________

Materials: Spring scale, two metals cylinders of the same weight, an elastic,and a tub of water.

Method: Manipulated variable: Kind of metal : Brass, Aluminium. Weigh the samples in air with spring scale. Responding Variable: Weigh the samples in water with spring scale. Record the results.

Observations:
Metal Weight 

in Air (N)

Weight 

in Water (N)

Difference  (N)
Aluminium 

Brass 

Summary of observations: __________________________________________________________

__________________________________________________________

Conclusions: 4.21 Measuring the Buoyant Force:

(Make use of the pictures p109 "Explanations please")

Weighing sinkers in water
 

Conclusion: The weight of the displaced water is _____________ the buoyant force . (same as,equal to, greater than) 

You can make the buoyant force work for you and float as follows: 

[1] either change the size and shape to displace more liquid 

[2] or reduce the mass.


4.22 A bit Like greek

Have you ever pulled someone out of water and into a boat or lifted a large rock out of water? How does their weight change as you pull them out of water? Theseactivities show how strong the buoyant force of water is. Liquids have a buoyant force. The buoyant force caused by a liquid or gas depends on the size and shape of the object.

This affects the amount of liquid displaced. When an

object displaces a liquid or gas it feels lighter as the buoyant force pushes up.

Answers to cryptogram: "A bit Like greek"

A bit Like Greek

Have you ever pulled someone out of water and into a boat or lifted a large rock out of water? How does their weight change as you pull them out of water? These activities show how strong the buoyant force of water is. Liquids have a buoyant force. The buoyant force caused by a liquid or gas depends on the size and shape of the object. This affects the amount of liquid displaced. When an object displaces a liquid or gas it feels lighter as the buoyant force pushes up.

4.23 Summary:

Cryptogram Key:

a b c d e f g h i j k l m

a b c d e f g h i j k l m

n o pq r s t u v w x y z

n o p q r s t u v w x y z

Objects which are big and weigh little are good

floaters.

Floaters can be made sinkers by either adding

ballast or making their

size smaller.

adding ballast makes them heavier than

the buoyant force. The buoyant force of the

liquid pushes up on the object. When

the buoyant force is weaker than the weight the

object sinks.

Making an object smaller so they

displace less water may also

make an object sink. Making the size

smaller causes it to have less

buoyant force. The weight then

sinks it.

Sinkers can be made floaters by either removing

ballast (weight) or increasing the

size.

Removing ballast by while keeping the same

size makes the object a better floater.

Remember the air balloon is an example of this.

Keeping the same weight while increasing

the size makes the object a better floater.

Objects which are big and weigh little are

good floaters.

Summary:Answers

Objects which are big and weigh little are good floaters.

Floaters can be made sinkers by either adding ballast or making their size smaller.

adding ballast makes them heavier than the buoyant force. The buoyant force of the liquid pushes up on the object. When the buoyant force is weaker than the weight the object sinks.

Making an object smaller so they displace less water may also make an object sink. Making the size smaller causes it to have less buoyant force. The weight then sinks it.

Sinkers can be made floaters by either removing ballast (weight) or increasing the size.

Removing ballast by while keeping the same size makes the object a better floater. Remember the air balloon is an example of this.

Keeping the same weight while increasing the size makes the object a better floater. Objects which are big and weigh little are good floaters.

4.25 Crossword Review

Clues:

Water pushed out of the overflow by the wood is 1 .

Gravity pulls on a scale with a force called 2 .

A rig which can adjust the level of sinking is a 3 .

The amount of material measured in grams is 4 .

All under water (to sink) 5 .

6 water is used to sink a semisubmersible.

The 7 force pushes up on things in water.