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1. Chapter 3
Section 2, 3 and 4
Floating and Sinking
Created by: Hamdy Karim
Grade level(s): 8th grade
Subject area: Science

2. KS Standards and Activity Instructions
:Standards/Indicators
.) Use KS standards, not district standards. Include both number and standard description as well as indicator (
Grades 8-9
STANDARD 2: PHYSICAL SCIENCE- The student will apply process skills to develop an understanding of physical science including: properties, Solids, Liquids,
. and Gases
Benchmark 3: The student will investigate Floating and Sinking of different Objects
?.Indicator 2: Describes, measures, and represents data on How do they calculate the density by knowing the mass and volume of an object
:Activity Instructions
..Slide 3- Click on the numbered list 1-4 to open questions for discussion for the class related to the floating and sinking of some objects like Pepsi cans, ships......etc
.Slide 4- Continue the class discussion, click on the hidden definition of "density", and see if the new definition changes the classes answer to the first question
.Slide 5- Read slide 5 to the class
Slide 6- Read each blue card to the class. Have students hold up one finger if they think it is in motion, and two fingers if they don't think the situation is describing motion.
.Once the class is showing their answers have a student click on the box to reveal the answer
.Slide 7- Introduce the vocabulary word "reference point". Have students create a list of reference points they could use while sitting on a bus
.Slide 8- Click on the numbered list to open questions for class discussion
Slide 9- Introduce the metric system. Pass out meter sticks for students to look at. Show them each of the measurement units identified on the stick. Give students practice
. using units by completing the "Metric Inventory 2" document attached
Slide 10- Go over density formulas, emphasizing difference between constant and average speed. Practice calculating speed by completing "Bubble Gum Physics" handout
.attached

3. Floating and Sinking
struck an iceberg and divided into
two. Both pieces sank to the
bottom of the Atlantic Ocean. More *
than a thousand people died. In e pts t of the
C onc effec
April 1912, the Titanic departed Key is the ce sity
*
t r en
wha yant fo use d r an
from England on its first and only o u
?bu can yo wheth k in a
e
n
voyage. At the time, it was the How termine at or si
e o
largest ship a float nearly three to d t will fl
c
football fields long. the Titanic was obje
id
?flu
also the most technologically
advanced ship in existence. Its hull
was divided into compartments,
and it was considered to be
unsinkable. But unfortunately the
ship struck an iceberg and divided
into two pieces that sunk into the
bottom of Atlantic Ocean

4. How is it possible that huge·
ships made of steel can float
?easily in water
Yet in a few hours the same·
ship can become a sunken
.wreck like the Titanic
Why does most of an·
iceberg lie hidden beneath
?the surface of the water
To answer these questions,·
you need to find out what
makes an object float and
.what makes an object sink

5. Comparing Densities
One reason objects float or sink is
.their density
An object that is more dense than ·
the fluid in which it is immersed
.sinks
An object that is less dense than ·
the fluid in which it is immersed
.floats to the surface
If the density of an object is equal
to the density of the fluid in which
it is immersed, the object neither
rises nor sinks in the fluid; it floats
.at a constant level

6. Comparing Densities
Now you know why
lead sinks: it is
several times
. denser than water
Cork, which is less
dense than water,
.floats
Is an ice cube more
or less dense than
?water

7. Iceberg straight
! ahead
An ice cube floats in water
because the density of ice is
. less than the density of water
!But it’s just a little less
So most of a floating ice cube
.is below the surface
Since an iceberg is really a
very large ice cube, the part
that you see above water is
only a small fraction of the
. entire iceberg
This is one reason why
icebergs are so dangerous to
.ships

8. Buoyant Force
If you have ever picked up an object
under water, you know that it seems
.lighter in water than in air
Water exerts a force called buoyant
.force that acts on a submerged object
Buoyant force acts in the upward
direction, against the force of gravity,
.so it makes an object feel lighter

9. Weight vs. Buoyant Force
There is always a
downward force on a
.submerged object
That force is the weight
. of the object
If the weight of the
object is greater than the
buoyant force, the object
What can you infer about the
. will sink weight and buoyant force from
If the weight of the ?the picture
object is less than the
buoyant force, the object
will begin to float

10. Archimedes’ Principle
You know that Archimedes discovered that a submerged
object displaces, or takes the place of, a volume of fluid equal
. to its own volume
Using this idea, Archimedes came up with a principle that
relates the amount of fluid a submerged object displaces to
. the buoyant force on the object
It states that the buoyant force on an object is equal to the
.weight of the fluid displaced by the object
Therefore, the more fluid an object displaces, the more
.buoyant force it will have
The more surface area an object occupies, the more water is
. displaces
This is why it is easier to float in water when you are lying
down on your back – you take up more surface area,
displacing more water, therefore creating a greater buoyant
.force

11. Floating by changing mass
Changing the density of an object can make it
.float or sink in a given fluid
Even though you cannot change the density
of an individual substance, you can change
the overall density of things that are made of
.several materials
Submarines can change their overall mass,
and therefore their density to allow them to
. float and sink
They do this by filling or releasing water from
.their flotation tanks

12. When water is pumped out of its flotation tanks,
.the overall mass of the submarine decreases
Since the volume remains the same, its density
.decreases when its mass decreases
.So the submarine will float to the surface
What do you think a submarine does in order to
?sink
. To dive, the submarine takes in water
In this way, it increases its mass (and thus its
!density) and sinks
Most ships are also designed to alter their
.overall density
The hull (bottom part) of a ship contains a large
. volume of air
This air reduces the ship’s overall mass, and
.therefore its density, and helps it to float

13. Floating by changing volume
.Another way of changing density is to change volume
If the mass is kept the same, increasing the volume of
.a substance, will decrease its density
Increasing the surface area of a substance, will also
.increase its buoyant force
This is because the greater the volume of water
displaced, the greater the buoyant force (Archimedes
(.Principle
The shape of a ship causes it to displace a greater
volume of water than a solid piece of steel of the
. same mass because it has a greater surface area
!The more water it displaces, the easier it will float
A ship stays afloat as long as the buoyant force is
.greater than its weight

14. Pascal’ s Principle
Pascal discovered that pressure
increased
by the same amount
throughout an enclosed
or confined fluid. When force is
applied to
a confined fluid, the change in
pressure
transmitted equally to all parts
. of the fluid
This relation known as Pascal’s
.principle

15. Bernoulli’s Principle
It states as the speed of a moving fluid
increases, the pressure within the fluid
.decreases