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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
Changehttp://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
Credits: ESA
1 22
Gm mF
rwhere:
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
G is the gravitational constant
1 22
Gm mF
r
Credits: ESA
Determine the units of the gravitational constant.
1 22
Gm mF
r
Credits: ESA
2
1 2
FrG
m m
Credits: ESA
The units of the gravitational constant are N m2 kg–2.
2
1 2
FrG
m m
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.
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?
1 22
Gm mF
r
If Newton’s theory is correct, why don’t we
notice the effects in everyday life?
1 22
Gm mF
r
If Newton’s theory is correct, why don’t we
notice the effects in everyday life?
What assumptions are made in this calculation?
Credits: ESA
How does this formula link to the formula we have used connecting weight, mass and gravitational field strength?
1 22
Gm mF
r
Credits: ESA
How does gravitational force vary with distance?
1 22
Gm mF
r
Credits: ESA
The gravitational force is always attractive. Is this true of electrostatic and magnetic forces?
1 22
Gm mF
r
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?
Credits: ESA
How does this formula link to the formula we have used connecting weight, mass and gravitational field strength?
1 22
Gm mF
r
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
The theory of universal gravitation can be used in space travel.© ESA
One of the most famous lines in history…
Watch the extracts from Apollo 13© ESA
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
© NASA
Within your home group create a mind map of your knowledge and understanding of the solar system and its formation.
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
© NASA
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.
http://www.nasa.gov/images/content/162284main_image_feature_693_ys_full.jpg
© NASA
Examine this image from the Spitzer and Hubble telescopes.What information can we get from this image, and others like it?
http://www.nasa.gov/images/content/162284main_image_feature_693_ys_full.jpg
Amend your mind map to include this new information.
© NASA
Where did the moon come from?
Something more to consider:
http://www.nhm.ac.uk/nature-online/space/planets-solar-system/moon/origins/index.html
© NASA
Further sources of information:
Cloud collapse simulations (face on and edge on)
http://www.ifa.hawaii.edu/~barnes/ast110_06/quizzes/disc06.html
© NASA
Further sources of information:
http://earthobservatory.nasa.gov/Features/OrbitsHistory/
http://www.bbc.co.uk/programmes/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?
The birth (and death?) of our Sun
© ESA
© NASA
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.
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?
There is nothing new to be discovered in physics now. All that remains is more and more precise measurement.(Lord Kelvin, 1900)
Address to the British Association for the Advancement of Science, 1900
©Hunterian Museum and Art Gallery, University of Glasgow. Licensor www.scran.ac.uk.
' 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.'
Quoted in Invisible Light (1900) by George Woodward Warder
©Hunterian Museum and Art Gallery, University of Glasgow. Licensor www.scran.ac.uk.
'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.'
Presidential Address to the Institution of Electrical Engineers', 1889
©Hunterian Museum and Art Gallery, University of Glasgow. Licensor www.scran.ac.uk.