A presentation by Katie Luukas. #SciChallenge2017

1. GRAVITYBy Katie Luukas

2. What really is gravity?

3. Gravity has played a big part in making the universe the way it is;
•Gravity is what causes matter to come together to form planets, moons, and stars.
•Gravity is what makes planets orbit stars--like Earth orbits our star, the Sun.
•Gravity is what brings stars together in huge, swirling galaxies.
Definition;
The force that attracts a body towards the centre of
the earth,
or towards any other physical body having mass.
Gravity is the force that brings together all matter (Anything you can physically
touch). The more matter, the more gravity, so things that have a lot of matter such as
planets and moons and stars pull more strongly. Mass is the amount of matter in
something.
Gravitational force-Force of attraction between masses. This is only really
noticed when one of the masses is extremely big.
Every time you jump, you experience gravity. It pulls
you back down to the ground. Without gravity,
you'd float off into the atmosphere -- along with all
of the other matter on Earth.

4. Where does gravity come
from, and how does it
work?

5. Newton's law of universal gravitation-Published in
1687 Newton's law of universal gravitation
was the first idea that all bodies with
mass pull on each other across space.
He observed that the gravitational
force between two objects is
proportional to the masses of the two
objects and inversely proportional to
the square of the distance between
them.
1. A force is needed to change motion
2. Acceleration is proportional to the resultant force.
3. Every action has an equal and opposite reaction.
Two objects exert a force of attraction on one another
known as "gravity." Sir Isaac Newton quantified the
gravity between two objects when he formulated his
three laws of motion:

6. Matter does not pull on other matter across empty space, as Newton had imagined.
Rather matter distorts space-time and it is this distorted space-time that affects other
matter. Mass placed in a region of space will lead to a distortion of space-time. Empty
space-time is flat.
Objects warp the space-time around them , causing it to become curved, this causes
objects to experience gravitational attraction to each other.
Einstein's theory of General relativity–Published in
1916
Albert Einstein explained how gravity is more than just a force: it is a
curvature in the space-time continuum with his theory of relativity .
Einstein's theory of general relativity predicted that the space-time
around Earth would be not only warped but also twisted by the
planet's rotation.

7. How we know this theory is correct
Although instruments can neither see nor measure space-time, several of the phenomena predicted by its
warping have been confirmed, here are just some examples:
•Gravity Probe B was a satellite-based mission which launched on 20th April 2004 on a Delta II rocket. One
of its aims was to measure space-time curvature near Earth. This tested general relativity.
Initial results confirmed the expected geodetic effect (the effect of the curvature of space-time, predicted
by general relativity) to an accuracy of about 1%.
•A team of scientists announced in 2016 that they had heard and recorded the sound of two black holes
colliding a billion light-years away, this fulfilled the last prediction of Einstein’s general theory of relativity.
Physicists say, that faint rising tone, is the first direct evidence of gravitational waves, the ripples in space-
time that Einstein predicted. It completes his vision of a universe in which space and time are interwoven
and dynamic, able to stretch, shrink and jiggle.
• Irwin Shapiro proposed a test of general relativity. He predicted a time delay in the round-trip travel time
for radar signals reflecting off other planets. General relativity predicts a time delay that becomes
progressively larger when a particle passes nearer to the Sun due to the time dilation in the gravitational
potential of the Sun. Observing radar reflections from Mercury and Venus just before and after it is eclipsed
by the Sun agrees with general relativity theory at the 5% level.
•More recently, the Cassini probe has undertaken a similar experiment which gave agreement with general
relativity at the 0.002% level.

8. How gravity can
be used

9. Gravity assist
In orbital mechanics and aerospace engineering, a gravitational slingshot, gravity assist
manoeuvre, or swing-by is the use of the relative movement and gravity of a planet or
other object to change the path and speed of a spacecraft, typically to save propellant,
time, and expense. Gravity assistance can be used to accelerate a spacecraft, to increase
or decrease its speed or redirect its path. The "assist" is provided by the motion of the
gravitating body as it pulls on the spacecraft.
It was used by interplanetary probes from
Mariner 10 onwards, including the two
Voyager probes' notable flybys of Jupiter and
Saturn.

10. How humans challenge gravity

11. Artificial gravity
In space it is possible to create “artificial gravity” by
spinning your spacecraft or space station. When the
station spins, centripetal force acts to pull the
inhabitants to the outside. This process can be used
to simulate gravity.
Unlike real gravity, which pulls towards a centre of a
planet, the centripetal force pushes towards the axis
of rotation
R=Radius from centre of rotation
A=Artificial gravity
T=Orbital period

12. How gravity has shaped our universe

13. •The gravitational attraction during the formation of stars and planets caused them to take
on spherical shapes, which is the most efficient shape for evenly distributing the
gravitational force among the object's mass.
•Gravitation keeps the Moon in orbit around the Earth.
Since the Law of Inertia states that objects in motion tend to go in a straight line, the force
of gravitation between the Earth and the Moon prevents the Moon from continuing in a
straight path.
 It is somewhat like the effect of a string on a weight that you swing around you. Once
you let go, the weight no longer goes in a circular path but instead flies out away from you.
•Likewise, the Earth and other planets are in orbit around the Sun, and the Sun is in orbit
around the centre of the Milky Way galaxy.
•Objects in space are constant motion.
Besides causing quantities of matter to gather
together to form suns, planets and moons,
gravitation also causes these moving bodies
to interact with each other. If the paths of
two speeding objects in space intersect,
they will collide or spiral into each other.
Some of what gravity does

14. Gravity in Black holes
•A Black hole is a region of space having a gravitational field so intense that no matter or
radiation can escape-not even electromagnetic waves such as light.
•General relativity tells us that a sufficiently compact mass can deform space-time to form a
black hole.
•The gravity is so strong because lots of matter has been squeezed into a tiny space.
•As all this matter spirals into the black hole , friction between the particles(dust ,moons ,
planets, and even stars) creates massive heat and light like a ring of extreme light around
the black hole which helps astronomers detect them.
•Black holes can be big or small, scientists think that the smallest black holes are as small as
just one atom.
These black holes are very tiny but have the mass of a large mountain.

15. Albert Einstein first predicted black holes in 1916 with his general theory of
relativity. The term "black hole" was coined in 1967 by American astronomer
John Wheeler, and the first one was discovered in 1971. There are three
types: stellar black holes, super massive black holes and intermediate black
holes.
The discovery of Black holes

16. Gravity's Role in Making Stars
•When a clump of gas and dust is small and dense
enough, gravity plays a significant role in turning
that material into a new star.
•Stars form in cold, dense regions of space called
molecular clouds. When the force of gravity pulling in on the cloud is greater than the strength
of internal pressure pushing out, the cloud collapses into a protostar.
•Once started, the collapse of the solar nebula continues because the force of gravity exerted
on the cloud grows stronger as the cloud shrinks in size.
•Astronomers do not yet know, but how stars form is a puzzle of great interest to them, and
not only because we live around one.
•Young stars hold the clues to many cosmic wonders, from the production and dispersal of
new elements to the illumination of distant galaxies whose properties trace cosmic history.

17. What if there was no
gravity?
(Physics is adamant that this
could never actually happen)

18. •The most important things held to the Earth by gravity are the atmosphere and our water.
•Without gravity, earth's atmosphere and its oceans, rivers and lakes would be one of the first
things to drift away into space.
• If the Earth's gravity were ever to change significantly, it would have a huge effect on nearly
everything because so many things are designed around the current state of gravity
•Earth itself would most likely break apart and float off into space.
•Eventually there would be no clumps of
matter, like stars or planets, anywhere in
the Universe. There would just be a
diffuse soup of atoms and molecules,
drifting around not doing much.
•Without the force of gravity to hold the sun
together, the intense pressures at its core would
cause it to burst open in a titanic explosion.
•The same thing would happen to all the other
stars in the Universe.
What would happen to our universe?

19. •That is just what happens after a short visit to space. If you were to grow up without
gravity, all of the systems that depend on gravity like your muscles, or your balance system,
or your heart and blood vessels would develop differently.
•If gravity was not around for our hearts, muscles and bones to respond to, our organs
would almost certainly develop in different ways.
•Realistically, we would all die
What would happen to you;
•Our bodies are adapted to an Earth-like gravitational
environment. If we spend time living where gravity is
different, such as on board a space station, our bodies
change.
•It is now an established fact that astronauts lose bone
mass and muscle strength during stints in space, and
their sense of balance changes.
•An absence of gravity brings other problems. For reasons not entirely clear, our red blood
cell count falls, bringing on a form of "space anaemia". Wounds take longer to heal and
the immune system loses its strength.
•Even sleep is disturbed if gravity is weak or absent

20. What questions we have on gravity ,
and how they could be answered.

21. •If gravity is a force that causes all matter to be attracted to all other matter, why
are atoms mostly empty space inside?
•How are the forces that hold atoms together different from gravity?
•How can anything really stay hollow and not be pulled together into one mass by
gravity?
•These are big questions that scientists have wondered about these things for a
long time.
•What role does gravity play in shaping larger clouds of gas and dust, the ones that
have not yet formed such dense cores?
What we don't know:

22. •Fundamental Physics hopes
to discover and explore
fundamental physical laws
governing matter, space,
and time and to discover
and understand the basic
rules nature uses to build
the structures we see
around us.
•Scientists and engineers have developed new technologies and
instruments that will help us understand more about nature.
•These new instruments can be taken into space and do experiments
where the forces of gravity are very small, so scientists can do very
delicate experiments to see what single atoms do under special
conditions.
Fundamental physics

23. •Astronomers do not yet know, What role gravity plays in shaping larger clouds of
gas and dust that have not yet formed dense cores, but how stars form is a
puzzle of great interest to astronomers.
•Young stars hold the clues to many cosmic wonders, from the production and
dispersal of new elements to the illumination of distant galaxies whose
properties trace cosmic history.
Young stars

24. Thank you for watching this
PowerPoint.