Heavens above! - INAF -Astronomical Observatory of Padova

Heavens above!
K-8 Astronomy and Physics course
6th Module – Let’s deal with concepts
The aim of this module is to introduce an understanding of astronomical distances and of the
way in which they are measured. Moreover, it introduces students to the concept of Solar
System as a “physical system” and to the concept of (electromagnetic and gravitational)
“field”.
Users: Sixth/Seventh Grade Students. Total amount of time: 18 hours. Teaching proposal and
educational material, cards for students
Introduction
This Teaching Unit is addressed to sixth grade or seventh grade students. The expected time is around 18
hours, which can be condensed into a relative short period of time in the School year.
It is quite a simple Unit, as far as hands-on activities are concerned. On the other hand, it asks students
a big effort as far as concepts. In the first part, students are supposed to compare, to get used to and to
learn distances, units of measure and orders of magnitudes, which are essential for understanding
Astronomy. We will leave scale models behind, because outside the Solar System, it is no longer possible
to build them. The new phase is not mere calculation exercise. It is supposed to provide students with a
consolidation of the concept of “emptiness of matter” in the interplanetary space. Moreover, it is
supposed to teach them how to handle with confidence one of the fundamental parameters of the model:
the distance among bodies. However, Astronomy is that branch of Science, which goes from the infinitely
small (nuclear reactions, which feed the stars) to the infinitely large (structure of the Universe). Now,
students are asked to deal with this huge range of order of magnitudes.
The parallax method is the basic method for computing cosmic distances. The hands-on activity
developed in this T.U. is easy to carry out. Moreover, it is successful and it clearly shows the
phenomenon involved. Students are supposed to understand how the parallax is measured, at least from
a conceptual point of view. They are also supposed to understand that parallax provides the only direct
method for computing stars’ distances, which Astronomers can use. By means of the parallax, we cannot
measure far away distances. As a matter of facts, the smallest angle, which we can be measured
nowadays from the Earth’s surface, corresponds to 1/100 seconds of arc, while the smallest one from
space corresponds to 1/1000 seconds of arc. It is good to provide students with some examples of these
quantities, by some calculation development. For example, a parallax angle of 1/100 seconds of arc
corresponds to the arc, under which I see a Coke can from 4.000 km! Therefore, by means of this
method, we can compute distances of some hundreds of stars, among which, those which are the closest
to us in our Galaxy. In any case, it is important to repeat again and again and to have students
understand how important it is this direct method, which represents the base for the Distance Scale in
Astronomy. Every other measure of distance is indirect and it is based upon units of measure, which are
determined by means of parallax. In this part, we involve self-correction works, which we strongly
recommend. The purpose is to have students get used to self-evaluation and to have them develop a skill
concerning what computations are actually needed in problem solving.
In the second part, students will deal with the concept of “field”, which requires a major effort. It is also
fundamental for an understanding of distance interactions among bodies. This is an important abstraction
work, too, which starts from an analysis concerning characteristics and limits of phenomena. What makes
everything harder, is the fact that we cannot reproduce the “gravitational field” in the lab, which is what
we need now. We get to this concept, by involving other examples of central field, just like the
electrostatic one. Using more models, concerning the concept of field, is not confusing for students and it
helps them. As a matter of facts, it prevents common stereotypes from developing and it keeps children
from losing the “physical meaning”, which goes together with the theme. At the end of every hands-on
activity, we suggest to highlight the physical concepts, which constitute the basis of the activity itself and
the reasons, which led to simplification through model development.
The Night Under the Stars involves the projection of a well-know tape about order of magnitudes of
physical dimensions. It can be shown to students also during regular classes, too. Then, the Night
involves also a visit to an Astronomical Observatory. As you did for the others modules, you have better
talk with the person in charged.
1
What some of the teachers, who tested this module, think about it
“The hands-on activity turned out to be very interesting. Even those students, who usually find some
difficulties and therefore never take part in anything, happened to be “lively” during the lesson. In
particular, while building the scale Solar System model, they were impressed about the large distances
between each planet and the Sun.”
“The building of a scale Solar System model gave students an important hint to think, which went beyond
the astronomical concepts, which we were dealing with. Students discussed about the meaning of the
word model, about the limits of this model, about what the model provided an understanding of. They
reviewed and found an application for math concepts and instruments. They acquired manual skills, and
they though about why it was important to have the parts of the model done with precision. They learned
what a “system” is.”
2
6th Module Scheme, First part
6TH MODULE
TEACHING UNIT
To understand that
interplanetary space is empty
as far as matter.
Let’s deal with concepts
Aims:
6.0
What a scale Solar
System model tells us
To acquire fundamental
concepts concerning
Astronomy.
To rationalize some
astronomical concepts.
To correlate different physical
quantities.
6.1
To provide students with a
first understanding of
gravitational field.
The parallax
To provide students with a
first understanding of the
dimensions of the Universe.
To develop a critical eye, in
order to correctly weight
media means information.
OBJECTIVES
To understand that the
dimensions of the Solar
System bodies are negligible if
compared to the distances
among them.
A first step outside
the Solar System
To have students get used to
rigorous definition of
problems.
6.3
The astronomical
units of distance
6.4
From the concept of
field in general to the
concept of gravitational
field
“Emptiness of matter” inside
the Solar System.
“Structure” of the Solar
System: dimension/distance
relations among its members.
Angular shift, parallax angle.
To understand how we can
use the parallax phenomenon Relations among parallax
in order to measure distances. angle-distance of the objectdistance between the
To identify the limits of the observation points.
parallax method.
Diurnal parallax, annual
parallax.
To acquire the idea that also
outside our Solar System the
space in empty as far as
matter.
6.2
CONTENTS
To provide students with an
understanding of how
important it is, to choose the
right unit of measure for
astronomical distances.
Reference system.
Distance measurements.
Scale models.
To know the different units of
measure involved in
Astronomy.
Parsec, light year.
To understand which unit of
measure is more appropriate
to measure what.
Emptiness in the Solar System
and in the Solar
neighborhood.
To start giving an answer to
the question: what “keeps
together” those systems,
which are empty as far as
matter?
Order of magnitude.
Concept of physical system.
To introduce the concept of
field.
The Night Under the Stars
3
6th Module Scheme, Second part
TEACHING UNIT
6.0 What a scale
Solar System model
tells us
EDUCATIONAL
MATERIAL
Sample card for carrying
out the activity.
MATERIAL FOR
STUDENTS
Table about scale
distances and scale
diameters of the Solar
System bodies.
EXPECTED TIME
2 hours
Sample card for carrying
out the activity.
6.1
The parallax
6.2 A first step
outside the Solar
System
6.3
4 hours
Sample card for learning
evaluation.
Sample card for carrying
out the activity.
4 hours
Table about stars in the
Solar neighborhood.
Sample card for carrying
The astronomical out the activity.
units of distance
Power Point presentation
(distances among some
celestial bodies).
6.4 From the
concept of field in
general to the concept
of gravitational field
Sample card for carrying
out the activity.
The Night Under the
Stars
Plan for the Night: “How
far?”
Summarizing table
Recording table A (cell
phone-monitor).
2 hours
3 hours
Recording table B
(electrified spheres).
3 hours
4
Teaching Unit 6.0
“What a scale Solar System model tells us”
(Catch-up Unit, concerning fundamental concepts)
It is a catch-up Unit, which allows for repeating or introducing some important concepts. Among them,
we want to remember the “emptiness of matter” inside the Solar System.
Contents
“Emptiness of matter” inside the Solar System.
“Structure” of the Solar System: dimension/distance relations among its members.
Objectives
To understand that interplanetary space is empty as far as matter.
To understand that the dimensions of the Solar System bodies are negligible if compared to the distances
among them.
Glossary
“Empty as far as matter”.
Required time
Around two hours.
Needed material
A free space, which is big enough according to the scale factor, for a scale model (for example, a football
field, a long street, a bank…)
Plasticine or clay or whatever material, in order to build the planets and the Sun.
Procedure:
1.
2.
3.
4.
5.
Have students carry out a research in the Internet. They are supposed to look for data, which
allow them for building a scale Solar System model. These are the Sun’s dimensions, the
dimensions and the distances of the planets from the Sun (you may use the table we provided).
Choose the place, where to place the scale Solar System model (for example a large field, a
street…) and have students measure the largest distance, which they can count upon, in order to
place the planets.
Have students determine the scale dimensions and the scale distances, by taking into account
how big their space is. Have them fill in the table, which we provided, and which will be useful
later on.
Have students build the planets, according to the dimensions, which they determined. Students
are then supposed to place them on the ground, at the appropriate distances. If the field is not
big enough, you can skip the last planet (Pluto). In this case, it is important to have students find
out anyway, what would have been its position in the surrounding space.
Tell students to walk inside the scale Solar System model, in order to highlight the “emptiness of
matter”.
5
Teaching Unit 6.0: “What a scale Solar System model tells us”
Didactic-methodological suggestions
It is a fundamental T.U. for further concept acquisition. If you had already carried it out (see 5th Module,
T.U. 5.4), you could refocus students’ attention on the fundamental concepts in another way. You could
have them carry out a research in the Internet about scale Solar System models, which other classes
built, and you can have them analyze them. Some examples can be found at the Web sites:
www.lestelle.net,
www.aldini.comune.bologna.it/planetario/studenti/lulu/index.htm,
www.aldini.comune.bologna.it/8circolo/oggi/lavia.htm)
In order to consolidate these concepts, and to provide students with a first understanding of astronomical
distances, you can have them carry out the following consolidation activity. Take the Sun-Earth distance
as equal to one (in this way you start introducing the Astronomical Unit), and have students determine
the distances from the Sun of the other planets in astronomical units.
This step has to follow the previous activity, it cannot come before, otherwise we will involve two
different scales.
It is not necessary to carry out any evaluation test, since the scale model and the placing of the planets
themselves represent an evaluation test for the entire experience.
6
Teaching Unit 6.0: “What a scale Solar System model tells us”
Table about scale distances and scale diameters of the Solar System bodies
Object
Sun
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto
Diameter
(km)
Scale
diameter
(cm)
Distance from
the Sun
(km)
1.400.000
5.000
12.000
13.000
7.000
152.000
120.000
51.000
49.000
3.000
Scale
distance from
the Sun (cm)
0
58.000.000
108.000.000
150.000.000
228.000.000
778.000.000
1.427.000.000
2.870.000.000
4.497.000.000
5.900.000.000
End of Teaching Unit 6.0
7
Teaching Unit 6.1
“The parallax”
This T.U. introduces students to some concepts, each of which requires a hands-on activity. These
concepts represent essential knowledge in order to understand the parallax phenomenon and the parallax
method. Two fundamental points are highlighted: this is the only direct method in order to measure the
distances of celestial objects, and it represents the basis for building the astronomical distance scale.
Contents
Angular shift, parallax angle.
Relations among parallax angle-distance of the object-distance between the observation points.
Diurnal parallax, annual parallax.
Objectives
To understand how we can use the parallax phenomenon in order to measure distances.
To identify the limits of the parallax method.
Needed material
Students themselves, chalks, a meter, a goniometer, a window, some sheets of paper, pencils.
Required time
4 hours.
Glossary
Angular shift, parallax.
Procedure
Part A: Linear shift and angular shift
1.
Let’s observe the Moon, form an observation point (A) on the Earth (observer A). From here, the
Moon seems to be, let’s say, in the B position. After a little while, from the A position, we will see it in
the B’ position. Standing in A, how can I measure its shift? Students are supposed to identify the
two kinds of shifts, which can be measured. Then, they are supposed to notice that the only way for
measuring shifts in Astronomy is to measure angular shifts.
B
B'
A
Figure 6.1.1
While observing the Moon’s apparent shift in the Sky.
2.
You can have students visualize this fact by placing one of them in the A position, and another one in
the B position. Mark on the floor their positions and trace the line, which connects them. Tell the B
student to move to the B’ position. Mark the new position and trace the line, which connects him/her
to the A student.
8
B
B'
A
Figure 6.1.2
While carrying out the activity.
The A student is supposed to quantify the B student’s shift. Have students notice that two kinds of
measure are possible. The first one concerns the linear shift, while the second one concerns the angular
shift. Have them carry out both measures. Finally, have them discuss about what kind of measure can be
carried out as far as celestial objects.
Part B: An introduction to parallax
1.
Keep in mind that the only quantities, which we can measure on the celestial dome, are angular
shifts.
This easy hands-on activity allows for an understanding of “parallax angle”. At the same time, it
allows for carrying out the first measures. Have students fully extend their arm in front of them, and
have them hold their forefinger up. Have them observe the shift of their forefinger, with respect to
the background, by closing one eye at the time.
Have them graphically represent what they did (see figure 6.1.3).
Horizon, or background
D forefinger
Arm’s
length
Parallax
angle
A
B
Figure 6.1.3
Parallax angle and its measure.
2.
Tell students the right name for the ADB angle, i.e. parallax angle. The AB distance is equal to the
distance between each child’s eyes, and you can measure it. Both the DAB and the DBA angles can be
measured. What we have to determine is the DB distance (see didactic-methodological suggestions).
In this example, what moves is the observation point (i.e. the eye, from A to B), while the object (the
forefinger) is still. Introduce the concept that the same method is used for measuring distances of far
away objects, just like celestial objects.
3. Have students carry out the same activity, but with a slight change. Tell them to keep their forefinger
at different fixed distances from their eyes: 10 cm, 20 cm 30 cm…. Have them notice that the
parallax angle becomes smaller and smaller. The discussion, which follows, aims to have students
think about the necessity of testing the validity limits of this method.
9
Part C: How to measure astronomical distances by means of the parallax method
The AB distance (i.e. the distance between two observations) must be large enough, in order for the
parallax angle to be large enough to be measured. Discussions at the end of part A and part B have to be
focused on this fact.
If a Sky-object observer on the Earth waits for some hours, he/she will be able to measure the so-called
diurnal parallax. As a matter of fact, if the same person waits just some hours, he/she will be able to
determine parallax angles of celestial objects.
His/her position on the Earth changes thanks to Earth’s rotation (it is similar to the B case, see didacticmethodological suggestions). Therefore, he/she can take the arc of the circumference as basis. This arc is
exactly the one, which he/she has run meanwhile, due to Earth’s rotation.
Students are supposed to carry out a research either in the Internet or on textbooks. They are supposed
to find the values of the diurnal parallax of some bodies inside the Solar System: the Moon, the Sun,
Pluto. They are supposed to notice the fact that the further an object from the Earth, the smaller its
diurnal parallax. They are also supposed to notice that it is not possible to use this method for objects,
which are very far away from the Solar System.
In order to go further, it is necessary to take the diameter of the Earth’s orbit as the AB observation
basis. This allows for defining the annual parallax (it is the parallax measured by taking this diameter as
the basis). Have students look for some values of annual parallax: Proxima Centauri: 0.762’’ (it is in
Centaurus constellation, Southern Hemisphere); 61 Cygni: 0.293 ” (it is in Cygnus constellation, or
Northern Cross); alpha Lyrae 0.261” (it is Vega).
From the discussion, it has to come out once again, that the further an object from the Earth, the smaller
its annual parallax. Somewhere, it is not possible anymore to measure any angle.
Didactic-methodological suggestions
Hands-on activities should be carried out by students divided in groups, but every student is supposed to
collect data on his/her notebook.
Part A: keep in mind that the range of time has to be short enough, so that we can say that the
observation point didn’t move. In order to widen the concept of parallax, and in order to repeat the
concept of reference system, it is important that the activity about the angular shift of the Moon is carried
out by students (divided in groups).
Part B: if children have already studied similitude, it is easy to go on. All you have to do is to build a
triangle, which is similar to the previous one, and of which we know the dimensions, and to make the
similitude.
D
E
A
H
B
Figure 6.1.5: Let’s use similar triangles
For example, take EB as equal to 1 cm; trace the parallel line to AD, which intersects AB in H; the HB
segment can be measured on the drawing, therefore we can write the following similitude: EB:DB=HB:AB
where the only unknown quantity is DB (length of the arm).
Part C: Keep in mind that the method we showed is not precisely coincident with the one, which is used
in Astronomy. As a matter of facts, we worked on a flat surface, while astronomers have to take into
account the three-dimensional nature of the problem; we assumed we knew the distance, while what
astronomers know is the parallax angle, which allows them for determining the distance. Hence the
importance of precision in celestial bodies parallax measures.
To tell the truth, it is very complex to carry out parallax measures. Just few professional men are able to
carry them out. The point of all this is that the values obtained for the distances by means of parallax are
the only direct measures, which the astronomical scale distance is based upon.
10
Teaching Unit 6.1: “The parallax”
Evaluation test
1.
Imagine there is a living creature on Mars. Deimos is one of the satellites of his planet. He wants to
determine the distance of Deimos from Mars, but he is does not know how to do it, and he asks you
for help. Circle the pieces of information, which you need, in order to help him with his calculation.
The parallax of Deimos.
The revolution period of Deimos around Mars.
The rotation period of Deimos on its axis.
The Mars’ dimensions.
The Earth’s dimensions.
2.
Circle the right answer.
Tell the living creature that the diurnal parallax of the Moon is (57’2’’.44). Following exactly what you
did for Deimos, he wants to determine the parallax of the Moon from his own observation point. He
will obtain:
the same value
3.
a bigger value
Circle the right answer.
For the living creature, who lives on Mars, the diurnal parallax of the Sun is, with respect to the one
measured from the Earth:
bigger
4.
a smaller value
smaller
Circle the right answer.
Distance between the two observation points being equal, the bigger the distance of an object from
an observer, the ……… its parallax angle.
a) bigger
b) smaller
5.
Circle the right answer.
Distance between the observer and the object being equal, the bigger the distance between the
observation points, the ……… the parallax angle.
a)
b)
bigger
smaller
End of Teaching Unit 6.1
11
Teaching Unit 6.2
“A first step outside the Solar System”
This T.U., as well as the next one, is a passageway between two worlds. The first one involves
dimensions, which students are normally used to. The second one involves dimensions, which are
necessary in order to study celestial bodies. This T.U. involves again scale models, in order to have
students understand that it is necessary to use other units of measure. Moreover, we will keep talking
about “emptiness of matter”.
Contents
Reference system.
Distance measurements.
Scale models.
Objectives
To acquire the idea that also outside our Solar System the space in empty as far as matter.
To provide students with an understanding of how important it is to choose the right unit of measure for
astronomical distances.
Needed material
Either Internet connection or some texts, in order to come up with a list, which contains 8 stars among
the closest ones to the Sun. You may make a transparency of the table, which we provided.
Required time
Around four hours.
Glossary
Galaxy, light year, parsec, astronomical unit.
Procedure
1.
2.
3.
4.
5.
6.
7.
Have students carry out a research either on the Internet or on textbooks, in order to find the
distances of eight stars, among the closest ones to the Sun. They are part of our system (i.e. our
Galaxy).
Take into consideration again the dimensions of the place, where you built the scale Solar System
model. With this value, have students try to develop a scale model of the Sun and of its closest stars.
Ask them if they agree to consider all these stars as having the same Sun’s dimensions. If the Sun
were a 1cm-diameter sphere, at what distance would the other stars be?
Since it is impossible to build the scale model, it is supposed to be at least set up. The aim is to reach
the conclusion that the dimensions of these stars would be negligible, if they were compared to the
distances among them.
Point out the fact, that if we scale the distances among the stars, their diameters will be scaled by
the same factor.
During the discussion, lead students to the conclusion that the space outside the Solar System is
empty as far as matter, too.
It is important to have students notice that we are still inside our Galaxy, or better in the Solar
neighborhood. Even interstellar space is empty as far as matter.
Didactic-methodological suggestions
No evaluation tests are provided, since the hands-on activity is very simple, but effective.
We suggest to have students carry out steps 1 to 4 in groups. We suggest to carry out discussions in the
end, so students can take part by reading their notes.
Just because “emptiness of matter” in our Galaxy has to come to the eyes, we suggest to give students
the freedom to choose their own scale factor. Only in a later time, have the groups compare, what each
of them came up with, and discuss about the different choices.
12
Teaching Unit 6.2: “A first step outside the Solar System”
Table about stars in the Solar neighborhood
STAR’S NAME
Alpha Centauri
Barnard Star
Alpha Canis
Majoris
Epsilon Eridani
61 Cyg A
Alpha Canis
Minoris
Epsilon Ind
Eta Cassiopeae
DISTANCE
(scale)
DISTANCE
13
4* 10
km
5.4*10 km
13
7.5*10 km
13
9.6*10 km
13
10.4* 10 km
13
10.5* 10 km
13
10.8* 10 km
13
11* 10 km
13
Every distance is measured from the Sun; remind the value of the Sun’s diameter.
Scale factor used = diameter of the ball / Sun’s diameter
End of Teaching Unit 6.2
13
Teaching Unit 6.3
“The astronomical units of distance”
By now, kilometer has been the only unit of measure, which we used. Now, we introduce the units of
measure, which are really used in Astronomy: the Astronomical Unit, the light-year and the parsec. This
lesson is supposed to be carried out either by means of a Power Point presentation or by means of a set
of transparencies. The transparencies are supposed to be overlapped one by one, in order to allow for a
quick presentation of these quantities.
Contents
Parsec, light year. Order of magnitude. Emptiness in the Solar System and in the Solar neighborhood.
Objectives
To know the different units of measure involved in Astronomy.
To understand which unit of measure is more appropriate to measure what.
Needed material
Table with distances of the closest stars to the Sun.
PowerPoint presentation (or transparencies).
A copy for each student of the summarizing table.
Required time
2 hours.
Glossary
Light years, astronomical unit, parsec.
Procedure
1.
2.
3.
4.
5.
6.
7.
This activity involves a PowerPoint presentation (or a set of transparencies) about some tables. They
allow for a comparison among the distances of some celestial bodies computed using different units of
measure.
The transparencies are supposed to be overlapped one by one. At the same time, students are
supposed to answer the question (see summarizing table). The next transparency provides students
with the correction of their previous answer.
Have students discuss upon the first table and upon the method involved in choosing its members.
Ask students to try to give a reason why there are some empty spaces in the tables. While trying to
explain, students are supposed to come up with a sort of summary of the lesson.
Introduce the parsec, as the distance to an object, which shows an annual parallax of one second of
arc. It is equal to 3.26 light years, i.e. 206.265U.A. or 30.860.000.000.000 km.
Tables have to be presented one next to the other, so that students can carry out the required
calculations and later they can check them.
By means of direct trigonometric parallax, we can measure distances up to 500 parsecs. Therefore
we can come up with an approximate value of how many objects there are in a 500-parsec-diameter
spherical volume centered on the observation point.
Here, the Earth is considered as the point, from which distances are measured. Keep in mind that the
same thing can be carried out from whatever position, and that the Sun-Earth distance is negligible if
compared to distances among stars.
Didactic-methodological suggestions
No written evaluation tests are provided: students are supposed to fill in just a summarizing card. This
card allows for self-correction of the answers. It is important, because it allows for an immediate selfevaluation.
The concept of light year has to be passed on to students as a simple definition: it is the distance, which
the light runs in a year at almost 300.000 km/sec. The light year is a unit, which is not that used by
Astronomers, but among popularizers. That’s the reason why children know it. Be careful at the fact that,
often students confuse distance and time, because the word “year” is misleading.
It is important to keep in mind that here the Earth is considered to be in a central position, but this idea
could allow for misconceptions about the Earth’s position in the Universe.
14
Teaching Unit 6.3: “The astronomical units of distance”
Summarizing table
(to be given to students, who have to fill it in during the lesson, and who need it for answering
to teacher’s questions)
Determine the order of magnitude of the distance of the celestial bodies from the Earth, which you see in
the first column on the left side in the PowerPoint presentation. Write the values here.
Compare them to the values, which are now provided in the presentation and correct the wrong ones
with a different color.
Now, let’s consider the Astronomical Unit. What is an Astronomical Unit? Write your answer.
Now, let’s observe the light-year values. Explain why the squares of the first five stars are empty.
Now, it the parsec time. What can you say, about the values, which are written in the last table? Would
you leave them as they are, or how would you modify them?
End of Teaching Unit 6.3
15
Teaching Unit 6.4
“From the concept of field in general to the concept
of gravitational field”
In this T.U. students will be provided with a general and qualitative approach to the concept of field.
Then, they will be introduced to the concept of gravitational field. This concept is important for a better
understanding of the Solar System.
Contents
Concept of physical system.
Objectives
To start giving an answer to the question: what “keeps together” those systems, which are empty as far
as matter?
To introduce the concept of field.
Required time
Around 3 hours.
Needed material
A computer, a cell-phone, a meter.
Glossary
Gravitational attraction.
Field.
Gravitational field.
Procedure
1.
2.
3.
4.
5.
6.
7.
8.
Put a cell-phone close to a computer monitor and have students notice what happens when the cellphone is not working.
Have students notice what happens when the cell-phone rings, by pointing its antenna towards the
monitor.
Measure the distance, from which effects are produced on the monitor.
Direct the antenna of the cell-phone towards other directions. Again, have students notice the effects
and find out the distance. Data have to be collected and plotted in a graph (recording card A).
Discussion about data. Students are supposed to notice that there is an interaction between the cellphone (considered as a system: antenna+software+display), and the computer system
(monitor+computer+software). The interaction is caused by something, which our senses cannot
perceive. Tell students, that according to a physical model, this interaction is considered as due to an
intermediary. It is called “electromagnetic field”. It is generated by a source, which transmits (field
source). According to the model, there is “something”, which we cannot see, which allows for
distance interaction between two systems, the cell-phone and the computer. Be careful at students’
materialization of this “something”. The field is a characteristic of the space, which is due to the field
source, and which is noticed when a “testing body” is introduced (a mass in a gravitational field, an
electrified sphere in an electrostatic field).
Ask students if they know other kinds of interactions among complex systems or among objects.
Have them analyze differences and analogies among the different interactions (TV remote control and
the like, radios, satellite TV, etc.). What students are supposed to highlight are the directional nature
of all these interactions and the fact that the bigger the distance, the weaker the effect (not linear
relation).
In any case, introduce the concept of interaction in an operational way. You can do that by means of
simple activities, such as showing students the electrostatic interaction, which is present between two
electrified spheres, which hang from the ceiling (recording table B).
You can say, that we can express interaction in two ways: a) every sphere is under a force, which is
due to the other one; b) every sphere is under the control of something, which we cannot see, which
is due to the other sphere, and which we call “electrostatic field”. Specify that, in every case but the
cell-phone one, the origin of the field is supposed to be chosen depending upon the reference system
(for example, I can say that the sphere B is in the field, which is generated by the sphere A, or the
other way around).
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9.
Have students start thinking about gravitational attraction, by letting an object fall down (it must not
bounce!). Discussion. Students are supposed to notice that its falling down is once more directional,
towards the center of the Earth (see didactic-methodological suggestions) and that attraction is
involved again. Introduce the concept of gravitational force and gravitational field (of a well specified
object) as a central field.
10. Have students determine how long it would take to the Moon to fall on the Earth, if there were just
the gravitational attraction (i.e. the gravitational attraction force between the Earth and the Moon).
Have students start thinking about the fact that what allows for equilibrium in stellar systems could
be the gravitational field.
Didactic-methodological suggestions
It is a qualitative hands-on activity, but nonetheless, it allows for focusing students’ attention on the
concept of field. It is important to have students understand, that the further we move from the object,
which generates the field (the one considered as the field source), the more the effects of the field itself
diminishes. Even if the electromagnetic field and the gravitational field are very different, we chose
anyway to use cell-phones in order to introduce the concept of field. The reason is because it is very
common to hear (Italian) people say “there is no field” when the cell-phone does not transmit and when
it does not receive.
If you want to show students other examples concerning fields, remember that they should have the
same characteristics of the previous one. In particular, they should not be visible in every day
experience, so that their detection in the lab makes the activity be more affective. You can replace the
monitor with a regular telephone: if you talk on the phone and if you make a near-by cell-phone ring, you
will obtain the same effect. Or you can listen to the radio, and you can make a near-by cell-phone ring.
If you want to use two magnets, you have to be careful. What you want to pass on to students is the
concept of central field, while with magnets, the field is always generated by a dipole (magnets have to
poles, it is not like the electric charge).
Just because there are qualitative activities, we provide no evaluation tests.
Concept consolidation activity
1.
As a final activity, you can show short movies about gravitational attraction. In particular, we mean
movies, which concern with space lunches. Or you can tell students how scientists found out the way
to send space shuttles in the space, against the gravitational attraction.
2.
Historical researches about the discovery of the universal gravitational law.
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Teaching Unit 6.4: “From the concept of field in general to the concept of gravitational field”
Recording table A
(step 4 of the procedure)
Distance between cellphone and monitor (in
cm)
Description of the effects (video vibration, image swaying,
noise…)
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Teaching Unit 6.4: “From the concept of field in general to the concept of gravitational field”
Recording table B
(step 8 of the procedure)
Distance between the
electrified spheres (in cm)
Description of the visible interaction between the spheres
End of Teaching Unit 6.4
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Teaching Unit 6.4: “The Night Under the Stars”
How far?
(Plan for the Night Under the Stars)
We suggest to split the Night into two parts, which can take place on two different days. The first part is
about the showing and the discussion of the video “Potenze di Dieci” (“Powers of ten”) (Zanichelli
publishing). The purpose is to study in depth and to consolidate the basis of stellar distances, which have
already been acquired while carrying out this module.
The second part can concern a visit to a professional Astronomical Observatory. It is necessary to tell the
director, what you want children to observe, i.e. planets, which might be visible at that time, some stars
having different colors, double systems, etc. If it is possible, references to the distances of these bodies
should be made.
It is better not to talk to children about galaxies, about the Universe, etc. They will study such themes in
the next year. Instead, it would be a good thing, if they could have some explanations and
demonstrations, about how instruments work.
For further explanations, about how to set up the visit or about what observatories you can visit, e-mail
to [email protected]
End of 6th Module
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