What do we know about gravity?. What is gravity? What is the force of gravity? What are the effects...

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

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

http://download.esa.int/qt/GOCE_counteracting_drag.mov





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


They also realised that the moon reflected sunlight.

© ESA


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



1 22

Gm mF

r



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.

© 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?

© 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


'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


What do we know about gravity?. What is gravity? What is the force of gravity? What are the effects...

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