Download Buoyancy - United States Sailing Association

Buoyancy
How does this boat float?
Module 2: Chapter 2
Level
Summary
Standards
Middle School
Subject Areas
Students investigate the concepts of
buoyancy, density, and water
displacement.
Click Here for a list of aligned Next
Generation and Common Core
Standards
Engineering, Mathematics,
Science, and Technology
Objectives
Duration
Lesson Time :
Part I: 40 Minutes
Part II: 40 minutes
Part III: 60 - 100 minutes
Setting
Indoor/Outdoor/On the
water
Skills
Predict, test, explain
Vocabulary
Gravity, Weight, Mass,
Displacement, Buoyancy,
Density, Center of Gravity
Students will:
 Predict whether an object will sink
or float when placed in salt and
fresh water.
 Identify factors that affect the
ability of an object to float.
 Explain the relationship of
buoyancy and density.
 Explain how both sailboats and
tankers can float even though they
are so heavy.
 Feel safer on a boat and encourage
kids to wear PFDs.
Materials
 US Sailing – Learn Sailing Right!
Beginner Chapter 2
 Student sheet 1
 One half stick (about 2 ounces) of
modeling clay (non-hardening) per
student
 One tub of water, at least six inches
deep, per four or five students
 One hundred large washers, e.g.,
1.5" fender washers (available from
hardware stores)
 Paper towels
 Ten objects that sink or float
 String and a float for testing objects
 Life jackets
Background
Buoyancy is the upward force
exerted on an object by the
surrounding fluid (in most case water)
in which the object is immersed.
Buoyancy acts against the force of
gravity.
Density
* If the density of an object is
greater than that of the surrounding
fluid, the object sinks.
Density of Object > Surrounding Fluid
= Object Sinks
*If the densities are equal, the
object is neutrally buoyant and hovers
in the fluid.
Density of Object = Surrounding Fluid
= Hovers
*If the density of the object is less
than that of surrounding fluid, the
object floats.
Density of Object < Surrounding Fluid
= Object Floats
Visit density and
buoyancy Interactive Simulations at
the University of Colorado to explore
the density and buoyancy of a variety
of objects and fluids.
Density is defined as the mass per
unit volume of an object. D=M/V.
Remind students that mass is not the
same as weight. Different fluids have
different densities. Since oil is less
dense than water, it floats on water.
Procedure
Part I (Classroom)
40 minutes
1. Ask students, “Do sailboats
float or sink?” Get several
responses to engage students
and explain their responses. The
interesting fact is sometimes
they sink and sometimes they
float.
6. Ask students, “why do sailboats
float? Does it make a difference if
they are in salt water or freshwater?
Let’s investigate.
7. Ask students, “what happens to
the water level in a bath tub when
you get in it?” (It rises) “Why?”
(when an object is placed in water it
takes up space, water is displaced
forcing the water level to rise - Water
Displacement.)
2. Tell students, “today we are
going to investigate why some
objects float and why some
sink?” “When we go sailing what
are some things that we think
will float? And some things that
may sink.”
3. Ask students to list things on
a sailboat or a motor boat that
may fall in the water while
sailing (ring dings, sunglasses,
hats, shoes, lifejackets, tools,
whistles, sails, tiller extensions,
rudders, motor, throw cushions
fishing poles, etc)
4. Ask students to predict
whether these objects will float
or sink and why. Categorize the
objects in the appropriate
columns.
That is, if an object weighs less
than the amount of water it
displaces then it floats otherwise it
sinks.
10. Have students investigate what
sinks and what floats using
Student Sheet 1. Students will
make a prediction and then they
will test the objects with their tub
of water in groups of four. Try to
keep objects sailing related.
8. Demonstrate this with two glasses
of water and an object that sinks.
9. Ask Students, “what forces are
effecting the object?” (there are two
primary forces acting on it, gravity
pushing down, and buoyancy
pushing up.)
11. Review the test results with
the class as a group.
Part II (Indoor Classroom)
40 minutes
1. Write on the board, "Create an
object out of clay that will float."
Give each student a half stick (2
oz.) of clay, and have several tubs
of water placed throughout the
classroom. Let them know they
5. This is an ideal time to tell
Note: The gravitational force is
can test their objects as often as
students about the body of
determined by the object's weight,
they like. (The paper towels can be
water they will be sailing on. Is it and the buoyancy force is
used to pat the clay dry before
fresh or salt water? How deep is determined by the weight of the
shaping into new designs). This
it? How much water the boats
water displaced by the object when it
should take no more than 5
require to go sailing?
is placed in water. If the gravitational
minutes.
force is less than the buoyancy force
then the object floats (a boat),
otherwise it sinks (a rock).
2. As students successfully
complete step 1, challenge them
with a new goal. Write on the
board, "Design an object out of
clay that can carry the largest
load of washers possible." Show
students the washers that will be
used to make up the load
(weight).
(Allow about 15-20 minutes)
3. As students work, encourage
them to continue making
improvements every time their
boats sink.
4. Show the best designed clay
boats to the class and ask them
what characteristics about these
designs carry a heavier load or
more weight.
5. So how do sailboats float? In
the 3rd century BC, the Greek
Mathematician Archimedes
realized that when he got into
the bathtub, his body displaced
the water making the water level
rise. His discovery led to two
laws of buoyancy that are still
the basis of shipbuilding today.
Law 1 states that any floating
object displaces a volume of
water whose mass is equal to
the mass of the object. Law 2
describes the effect the boat’s
shape has on how well it floats.
Part III (On the water)
60-100 minutes
1. Have students investigate the
hull shapes of the different boats
at your sailing center.
Show them the load/ safety
information on the boats. Ask them
to draw a few conclusions.
2. Have students rig the boats and go
sailing with an instructor at the helm.
While aboard discuss the hull shape
of the safety boat vs. the sail boat.
3. If time allows another addition to
this module is to test the objects the
students listed on the board from
part one. Tie a string and a float to
each object and toss it in the water
to see if it floats or sinks. This is a
great lesson about what to bring on
board for a day of sailing. (show wet
hats sink, sunglasses with croakies
float, and those without sink, and
most shoes sink.
Resources
1. This lesson was created from a
combination of The BRIDGE Ocean
Education Teacher Resource
Center Buoyancy: Don’t Even Sink
About It! and the Clay Boat Activity
from the Center for inquiry based
Learning.
2.Interactive Simulations at the
University of Colorado: Buoyancy
Simulator
Extension Activities
The Rutgers University Coastal
Ocean Observation Laboratory
(COOL) utilizes a fleet of
autonomous underwater vehicles
(AUVs) called gliders that fly
through the water column in a zig
zag pattern (up and down)
recording data such as salinity,
temperature, chlorophyll, sound
velocity, and more.
Intel Education: Float the boat –
Inquiry based learning exercises to
investigate buoyancy.
Student Sheet 1 Module 2
Name: __________________________
Date: __________________________
Sink or Float?
Object
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Prediction:
Actual: