What do we know about gravity?
What is gravity?
What is the force of gravity?
What are the effects of gravity?
What do we know about gravity?
How can we make use of gravity?
Mapping the gravitational field
© ESA
© ESA
GOCE flies at only 254.9 km.
What difficulty might this cause?
© ESA
GOCE experiences air
resistance or drag. It therefore
requires a propulsion system
to counteract the effects of
drag.
© ESA
What is GOCE’s mission?
Is this worth funding?
© ESA
Pair and share
GOCE Measurements Crucial to Understanding the Impact of Climate
Change
http://www.ipy.org/news-a-announcements/item/2180-goce-measurements-crucial-to-understanding-the-impact-of-climate-change
GOCE Satellite Views Earth’s Gravity in High Definition
http://news.bbc.co.uk/1/hi/8767763.stm
GOCE : listen to Professor Reiner Rummel, Chairman of the GOCE
Scientific Consortium, explain the benefits and uses of the data gathered
by GOCE http://news.bbc.co.uk/1/hi/8767763.stm
GOCE Facts and figures: http://www.esa.int/SPECIALS/GOCE/SEMDU2VHJCF_0.html
UK Space Agency: http://www.ukspaceagency.bis.gov.uk/18874.aspx
The 'standard'
acceleration due to
gravity at the Earth's
surface is 9.8 m s–2.
In reality the figure
varies from 9.788 m s–2
(minimum) at the
equator to 9.838 m s–2
(maximum) at the
poles.
GOCE measures this
using sensitive
gradiometers built
using six
accelerometers.
The resolution is 1 cm
in 100 km. That means
that for every 100 km
measured, the
measurement will be
accurate to within
1 cm. That’s accurate
to 1 in 1,000,000.
How does this compare
to the sensitivity and
experimental
uncertainties in our
gravitational field
strength
measurement?
Earth’s natural satellite
Greek philosophers
understood that the moon is a
sphere in orbit around the
Earth.
© ESA
Earth’s natural satellite
They also realised that the
moon reflected sunlight.
© ESA
Earth’s natural satellite
About 1850 years ago,
Ptolemy (90–168)
hypothesised that the
moon and the Sun
orbited the Earth.
What evidence was
there to support this
view?
© ESA
It was not until almost
1300 years later that
this view changed, with
the work of Copernicus
(1473–1543).
© ESA
Kepler (1571–1630)
developed three laws
which predicted that the
orbits of the planets are
elliptical, with the Sun at
the focus.
What evidence is there to
support this?
© ESA
Why does the moon
remain in orbit around
the Earth?
© ESA
Because of the force of
gravity – the weakest
of the four fundamental
forces and yet it keeps
the universe in shape!
© ESA
Newton (1642–1747)
developed the theory of
universal gravitation.
This was a very important
piece of work – not least
because he proposed it to
be 'universal‘, ie all parts of
the universe obey the same
laws of nature.
© ESA
Newton’s theory proposed
that the moon stays in place
as a result of the same force
that causes an apple to fall
from a tree.
© ESA
What evidence do we now
have to support this theory?
© ESA
Newton’s theory also
proposed that each body
with mass will exert a force
on each other body with
mass.
It said that the force of
gravitational attraction is
dependent on the masses of
both objects and inversely
proportional to the square of
the distance that separates
them.
© ESA
But Newton remained
uncertain. He was not
convinced that there could
be action at such a distance
without some medium, ie he
was concerned about the
distances over which this
force acts and the fact that
space is a vacuum.
© ESA
How would this theory be
written mathematically?
© ESA
Gm1m2
F
2
r
where:
F is force in newtons (N)
m1 and m2 are the two masses measured in kilograms (kg)
r is the distance between them (m).
Credits: ESA
Gm1m2
F
2
r
G is the gravitational constant
Credits: ESA
Gm1m2
F
2
r
Determine the units of the gravitational constant.
Credits: ESA
2
Fr
G
m1m2
Credits: ESA
2
Fr
G
m1m2
The units of the gravitational constant are N m2 kg–2.
Credits: ESA
The value of the gravitational constant
was determined by Cavendish (1731–
1810) in the late 1700s.
It was another hundred years before
Boys (1855–1944) improved on its
accuracy.
Credits: ESA
G = 6.67428 × 10–11 N m2 kg–2
as determined in 1895 by Boys.
G remains one of the most difficult
constant to measure with accuracy. In
2007 a further value was published
which suggested an improvement on
the accuracy.
Credits: ESA
G = 6.67 × 10–11 N m2 kg–2
is the value that we will use for
calculations in Higher Physics.
Credits: ESA
If Newton’s theory is correct, why don’t we
notice the effects in everyday life?
© NASA
If Newton’s theory is correct, why don’t we
notice the effects in everyday life?
Gm1m2
F
2
r
If Newton’s theory is correct, why don’t we
notice the effects in everyday life?
Gm1m2
F
2
r
If Newton’s theory is correct, why don’t we
notice the effects in everyday life?
What assumptions are made in this calculation?
Gm1m2
F
2
r
How does this formula link to the formula we
have used connecting weight, mass and
gravitational field strength?
Credits: ESA
Gm1m2
F
2
r
How does gravitational force vary with distance?
Credits: ESA
Gm1m2
F
2
r
The gravitational force is always attractive. Is
this true of electrostatic and magnetic forces?
Credits: ESA
How does the
gravitational
force affect
objects on an
atomic scale?
Newton’s theory suggests that gravitational
force acts over enormous distance. It is
suggested that it is the reason that the moon
remains in orbit around the Earth but what
about the effect of the moon on the Earth?
Gm1m2
F
2
r
How does this formula link to the formula we
have used connecting weight, mass and
gravitational field strength?
Credits: ESA
A short challenge: a simple model
Your challenge is to develop a simple model to
demonstrate to P7/S1 students the importance
of gravity in our solar system.
You must:
• use resources typically found in an ordinary
science laboratory
• be able to explain what your model
demonstrates
Gravity assist and slingshot
© ESA
The theory of universal
gravitation can be used
in space travel.
One of the most famous lines in history…
© ESA
Watch the extracts from Apollo 13
The principles of the gravity assist
method?
The advantages of it?
© ESA
We have explored the effects of the force of
gravity on a small scale, its importance in
satellite motion and its use in space flight.
We have discussed some of the historical
story associated with our understanding of
gravitational force, but we have yet to discuss
a very significant impact of the gravitational
force.
What do you
know about the
solar system?
What do you
know about its
formation?
© NASA
Within your home group
create a mind map of
your knowledge and
understanding of the
solar system and its
formation.
© NASA
Expert groups
Using identified web resources, you will each
work within an expert group to research one
area associated with the formation of the solar
system.
You will return to your home group and teach
others about your learning.
Expert groups
The purpose of the task is to:
• understand the development of theories
relating to the formation of the solar system,
and the evidence to support or refute the
theories
• consider the evidence for the role of
gravitational force in the formation of the
solar system.
University of Texas McDonald Observatory
website, StarDate Online.
http://stardate.org/astro-guide
Group Hubble: The Inner Planets & Exploring our own Backyard
Group Newton: The Outer Planets & the Realm of the Giants
Group Herschel: Minor Bodies & Remnants from the Beginning
Group Kepler: The Sun & The Solar System: Home Sweet Home
Return to your home group
and explain your expert
learning to your group.
As you go along, adapt
your mind map.
Add new information and
delete any information you
now know to be incorrect.
© NASA
© NASA
http://www.nasa.gov/images/content/16
2284main_image_feature_693_ys_full.j
pg
Examine this image from the Spitzer and Hubble telescopes.
What information can we get from this image, and others like it?
© NASA
http://www.nasa.gov/images/content/16
2284main_image_feature_693_ys_full.j
pg
Amend your mind map to include this new information.
Where did the moon come from?
Something more to consider:
http://www.nhm.ac.uk/natureonline/space/planets-solarsystem/moon/origins/index.html
Further sources of information:
Cloud collapse simulations
(face on and edge on)
http://www.ifa.hawaii.edu/~barne
s/ast110_06/quizzes/disc06.html
© NASA
Further sources of information:
http://earthobservatory.nasa.gov
/Features/OrbitsHistory/
http://www.bbc.co.uk/programm
es/p006t1ks
Watch BBC Wonders of the Solar System Episode 1
Empire of the Sun and Episode 2 Wonder out of Chaos
© NASA
Communicating science!
What would be the most
appropriate way to summarise
on an individual basis your
understanding of the
hypotheses on the formation of
the solar system and the
scientific evidence to support
these hypotheses?
© NASA
The birth (and death?) of our Sun
© ESA
This image shows a planetary
nebula. A sun-like star has
undergone 'death tremors' at the
end of its life. The star had difficulty
in getting enough fuel to keep up its
nuclear furnace, and has now shed
off some of its surface material in
two directions.
© NASA
Have we answered any or all of
these questions?
What is gravity?
What is the force of gravity?
What are the effects of gravity?
What do we know about gravity?
How can we make use of gravity?
Unanswered…
• Gravity as a property of space–time.
• The graviton as the exchange particle
of gravitational fields.
• The nature of mass.
• Black holes (and white holes?)
• What is the universe made of?
• Why does the gravitational mass of the
galaxy exceed the mass of the known
matter? Is there something else there?
Or do we not really understand gravity at
all?
• When were the first stars formed? What
were they like?
• Do gravitational waves exist?
• Why do the four fundamental forces have
the strengths they have?
• Is there a single unifying theory which
links gravitational force to the other much
better understood forces?
Address to the British Association for the
Advancement of Science, 1900
There is nothing new to
be discovered in physics
now. All that remains is
more and more precise
measurement.
(Lord Kelvin, 1900)
©Hunterian Museum and Art Gallery, University of Glasgow. Licensor www.scran.ac.uk.
Quoted in Invisible Light (1900) by George
Woodward Warder
' When asked if he leaned toward
the acceptance of any particular
theory of gravitation: 'No, no, no,
I accept neither theory, I accept
no theory of gravitation. Present
science has no right to attempt to
explain gravitation. We know
nothing about it. We simply know
nothing about it.'
©Hunterian Museum and Art Gallery, University of Glasgow. Licensor www.scran.ac.uk.
Presidential Address to the Institution of
Electrical Engineers', 1889
'This time next year,—this time ten
years,—this time one hundred
years,—probably it will be just as easy
as we think it is to understand that
glass of water, which now seems so
plain and simple. I cannot doubt but
that these things, which now seem to
us so mysterious, will be no mysteries
at all; that the scales will fall from our
eyes; that we shall learn to look on
things in a different way—when that
which is now a difficulty will be the only
commonsense and intelligible way of
looking at the subject.'
©Hunterian Museum and Art Gallery, University of Glasgow. Licensor www.scran.ac.uk.