Gravity Gravitation English Presentation Tugas Fisika Tugas Bahasa Inggris oleh : Kelas 12 IPA 6 SMA Negeri 1 Yogyakarta tahun 2014 Semangat!!!!!!! SUKSES

1. Gravity
XII IPA 6

2. Group 2
• Fita Aliftariasa (08)
• Kartikya Ishlah Utami (10)
• Rifda Latifa (16)
• Shinta Sigit Agustina (19)
• Muhammad Fauzi Dharmawan (23)
• Muhammad Ramadhani S. (25)

3. FORCES IN THE UNIVERSE

4. 1. Gravity
2. Electromagnetism
* magnetism
* electrostatic forces
3. Weak Nuclear Force
4. Strong Nuclear Force
Increasing
Strength
Kinds of Forces

5. Do you know what is Gravity?

6. • Gravitation, or gravity, is a natural phenomenon
which all physical bodies attract each other.
• It is most commonly experienced as the agent that
gives weight to objects with mass and causes them
to fall to the ground when dropped.

7. GRAVITY keeps the moon orbiting
Earth
It holds stars
together . . .
Prevents
planets
from losing
their
atmospheres . . .
And binds galaxies together
for billions of years . . .

8. FALLING BODIES

9. Falling objects accelerate at a
constant rate (Galileo):
Speed is gained at a constant rate:
9.8 m/sec/sec
“Acceleration due to gravity”
Ball
Earthp. 82

10. Time (sec) Speed (m/sec)
1 9.8
2 19.6
3 29.4
4 39.2
6 58.8
8 78.4
10 98
0
20
40
60
80
100
120
0 2 4 6 8 10 12
Speed (m/sec)
Time (sec)
Acceleration is same for ALL OBJECTS,
regardless of mass!

11. • Newton’s 2nd
law ⇒ force (F) is acting on
falling ball (mass = m)
• All masses have same acceleration
. . . so more mass means more force
needed:
mF ∝
F
m
Ball
Earth

12. F
• Newton’s 3rd
law ⇒ ball pulls on Earth
Ball
F
Does Earth accelerate?
Earth

13. UNIVERSAL GRAVITATION

14. All bits of matter attract all other bits of matter . . .
M1 M2
d
F F
“Inverse square law”
d
1
F2.
MMF1.
2
21
∝
∝
p. 92

15. 1. ⇒ Increase one or both masses, and force increases.
2. ⇒ Force decreases as distance increases.
Force Distance
400 N 10 m
100 N 20 m
25 N 40 m
16 N 50 m
4 N 100 m
d
M1 M2F F
4
400
2
400
100 2
==

16. Force Distance
400 10
178 15
100 20
44.4 30
25 40
16 50
11.1 60
8.2 70
6.25 80
4 100
0
20
40
60
80
100
120
0 100 200 300 400 500
Distance
Force
Force never becomes
zero.

17. Putting the two parts of the force law together . . .
2
21
d
MGM
F = (G = gravitational constant)
• Acts through empty space
“action at a distance”
• Explains how gravity behaves – but not why

18. WEIGHT

19. p. 83

20. Weight
• Measure of gravitational attraction of Earth
(or any other planet) for you.
Earth
R
F
m
M
Weight
2
R
GMm
FW ==

21. Other planets: M and R change, so your
weight must change
Mars: R = 0.53 x Earth’s radius
M = 0.11 x Earth’s mass
Earth Mars
Weight 150 lbs 59 lbs
A real planet . . .

22. “Weight” can be
made to apparently
increase . . .
p. 83
upward acceleration

23. . . . or decrease!
downward
acceleration
“Weightlessness”
9.8 m/s/s
Free-fall

24. EARTH’S MASS

25. 2
R
GMm
W =
your weight
your mass
Earth’s radius
Earth’s mass
M = 6 x 1024
kg

26. HOW DO THE PLANETS GO?

27. Planets appear
‘star-like’

28. Planets move, relative to the stars.

29. Planets reside
near Ecliptic.

31. [SkyGlobe]

32. Sun
Earth
Venus
Mars
Alien’s eye view . . .
Complicated!

33. Yet, patterns may be discerned . . .
• Planets remain near ecliptic – within Zodiac.
• Brightness changes in a regular pattern.
• Mercury & Venus always appear near Sun in sky.
• Mars, Jupiter & Saturn may be near Sun, but needn’t be.
• Planets travel eastward relative to stars most of the time,
but sometimes they reverse direction & go west!

34. Jupiter & Venus
are currently
“in”
Gemini.

35. Ancient
Greek
geocentric
solar
system

36. Motionless Earth
* Earth too heavy to be moved
* If Earth moved, wouldn’t we notice?
> Relative motion argument
> Parallax argument
Earth at center of Universe
* This is Earth’s ‘natural place’
> Heavy stuff sinks
* This is the natural place of humankind
> We’re most important (?)

37. Ptolemy
(85 – 165 AD)

39. Results: • Planet-Earth distance changes
• Planet sometimes goes backward

40. Nicolaus Copernicus (1473 – 1543)
• First modern
heliocentric (sun-
centered) model of
solar system
• Founder of modern
astronomy
• Not first astronomer!

41. Copernicus’
heliocentric
model,
simplified

42. Galileo Galilei
1564 - 1642

43. Galileo observes
Jupiter’s
four largest moons
Telescopic
View

44. Jupiter’s moons
in motion.
Allowed
possibility
that there
are many
centers of
motion –
not just Earth.

45. Venus shows a full set of phases –
like the moon’s

46. Venus’ motion according to . . .
Ptolemy
(new & crescent phases)
Copernicus
(full set of phases)

47. ORBITS

48. • Any motion controlled only by gravity is an orbit
Without gravity
With gravity
NEWTON: Gravity explains how planets (and
moons & satellites & etc.) go.
Sun

49. Several trajectories are possible. . .
Object is effectively
continuously falling
toward the sun . . .
. . . But never gets
there!
Circle
F

50. Imagine launching a
ball sideways near
Earth . . .

51. Possible trajectories:
• Circle
• Ellipse
• Parabola
• Hyperbola v
Which one you get depends on speed (v)!
“Escape”

52. Trajectories are
conics
These are only
possible orbits for
inverse square
law force.

53. • Circles & Ellipses: “Bound” orbits
• Parabolas & Hyperbolas: “Escape” orbits
v
v ≅ 5 mi/sec
v > 5 mi/sec
Escape:
v ≥ 7 mi/sec
Earth

54. KEPLER’S LAWS

55. Johannes
Kepler
(1571 – 1630)

56. “By the study of the orbit of Mars, we must either
arrive at the secrets of astronomy or forever remain
in ignorance of them.”
- J. Kepler
Tycho Brahe

57. 1. Planets move in elliptical orbits with the sun
at one focus
X
Sun (Focus)
Focus
Semi-major axis (a)
c

58. PerihelionAphelion
Earth: a = 1.00 AU = 92, 980.000 mi
aphelion = 1.0167 AU = 94,530,000 mi
perihelion = 0.9833 AU = 91,420,000 mi
67,000 mi/hr

59. Eccentricity (e): Measure of shape of ellipse
e = c/a a = semi-major axis
c = dist center to focus
0 < e < 1

60. a e
Earth 1.0 AU 0.0167
Mars 1.52 0.0934
Pluto 39.5 0.250
Halley’s Comet 17.8 0.967
A few objects orbiting the sun . . . . . .
Semi-major axis, or mean distance
between planet & sun

61. 2. A line drawn from planet to sun sweeps out
equal areas in equal times
2nd
Law
Demo

62. 3. The cube of the mean planet-sun distance
is
directly proportional to the square of the
planet’s orbit period
a3
= P2
a: AU
P: years
Or,
a3
/ P2
= 1 3rd
Law
Demo

63. P a P2
a3
P2
/a3
Mercury 0.241 0.387 0.058 0.058 1
Venus 0.615 0.723 0.378 0.378 1
Earth 1 1 1 1 1
Mars 1.881 1.524 3.538 3.538 1
Jupiter 11.86 5.203 140.7 140.8 0.999
Saturn 29.46 9.539 867.8 867.9 1
Uranus 84.01 19.19 7058 7068 0.998
Neptune 164.8 30.06 27156 27165 1
Pluto 248.5 39.53 61752 61768 1
0
10000
20000
30000
40000
50000
60000
70000
0 10000 20000 30000 40000 50000 60000 70000
Cube of semi-major axis
Squareofperiod
Solar System:

64. Newton modified Kepler’s 3rd
Law:
M
m
2
3
P
a
1 =
2
3
P
a
mM =+
units of the
Sun’s mass

65. SUN’S MASS

66. 3
2
2
a
m)G(M
4
P 





+
=
π
Mass of the Sun
1 yr
1 AU
Earth’s massSun’s Mass
M = 2 x 1030
kg ≅ 330,000 Earth masses (!)

67. CENTER OF MASS ORBITS

68. Finally (at last ) . . . the true story of orbits
We left something out . . .
Sun
Planet
Sun pulls on planet . . . planet pulls on sun
⇒ Sun moves a little, too!
Yikes!

69. Exaggerated view:
X
S
P
X = center of
both orbits
Circular orbits

70. Consider Jupiter & the Sun . . .
X
5.2 AU0.0052 AU
⇒ Sun’s motion is small!
Center of Mass
Gravitational
Orbits
Animation

71. Earth & Moon:
X
2900 mi 235,500 mi
2900 mi < Earth’s radius!
Gravitational
Orbits
Animation

72. Discovery of Neptune
1846: Presence of Neptune predicted
from irregularities in Uranus’ orbit.
(J. C. Adams & U. J. J. Leverrier)

73. Uranus
Neptune
Speeds up
Slows down