Chapter 29: Our Solar System - Crewes'n Science!



Chapter 29: Our Solar System

Motion and Forces

• Force – a push or pull one body exerts on another. Obvious or not, they are all around

• Balanced Forces – forces that equal in size and opposite in direction (Tug of war, gravity and normal force)

• Net Force – An unbalanced force that always changes the velocity of the object

- Tug of war when one force is more powerful than the other

- Will change its speed, direction or both

• Inertia – the tendency of an object to resist any change in its motion

- If an object is moving, it will keep moving at the same speed and in the same direction unless an unbalanced force acts on it

- If an object is at rest, it tends to remain at rest

- Bowling ball or ping-pong ball has greater inertia?

➢ The one with more mass will have more inertia. Speed or velocity is not a factor

➢ Basketball and a wiffle-ball bat

• Newton’s first law of motion (Law of Inertia) – An object moving at a constant velocity keeps moving at that velocity unless a net force acts on it, AND an object at rest, will stay at rest, unless a net force acts on it

• Friction - The force that opposes motion between two surfaces that are touching each other.

- Depends on the kinds of surfaces in contact and the forces pressing them together

- W/O friction: no walking, no holding things, no shoes, no clothes

Gravity

• Gravity – the attractive force that every object in the universe exerts on one another.

o Depends on two things: Mass and distance

▪ The larger the mass the greater the force between two objects (Earth, ball, and hand)

▪ The closer the objects are to each other the greater the attractive forces (satellite)

• Weight – The measure of the force of gravity on an object

- Not the same as mass

- Weight changes with the gravitational force, mass cannot change

- Mass measured in grams (g) and kilograms (kg) and weight is measured in newton (N)

- A 1 kg mass weighs about 9.8 newtons on Earth

- An average apple is about 4 newton

• When measuring weight, a scale is used. The weight is placed on the scale and gravity pulls it down. That weight is then balanced by a internal spring and a representative weight is given.

• Mass is measured by a scale also, but that scale is calibrated using known masses and is not balanced by a spring.

Accelerated motion

• Newton’s Second Law of motion – A net force acting on an object causes the object to accelerate in the direction of the force – Larger force means larger acceleration – a larger mass would require greater force than a smaller mass would require to achieve the same acceleration

- Also written as F = ma (force is equal to mass x acceleration)

- Mass is expressed in kg and acceleration in m/s2, so 1 kgm/s2 is equal to a Newton (N)

• Falling objects fall at the same rate, independent of mass

• Acceleration due to gravity is 9.8 m/s2 , therefore since the force of gravity is acting on the mass we can substitute weight for force to determine the weight of any object, or W = m x g

• This is true for any falling object

• Newton’s 3rd law – To every action force there is an equal and opposite reaction force – These forces are called action-reaction pairs – Some hard to see, others not so much – EX: Jumping from a boat, a trampoline, bullet from a gun, me standing on earth, swimmer in water, walking

- If there is no motion, all forces are equal. If there is unbalanced forces then there will be movement or acceleration

• Momentum – A property a moving object has because of its mass and velocity

p = m x v (momentum is equal to mass times velocity) – units are in kgm/s

- Momentum can change by changing either the mass or the velocity

- To calculate the change of momentum, just do the math – an object traveling at a certain speed has momentum, if you decrease the mass by half and double the velocity the momentum is the same as the original

- Momentum can be transferred to another object – pool balls – The momentum of the cue ball is transferred to the other balls

- Law of conservation of momentum – The total amount of momentum of a group of objects does not change unless outside forces act on the objects (friction) – loss of momentum can be attributed to sound, heat, or other modes of energy transport

29.1 – Overview of Our Solar System

• 9 planets and their moons all called satellites

• All lie in the same plane except Pluto

Early Ideas

• Ancient Astronomers believed in a geocentric model (Earth centered) – Everything orbited the Earth

• All planets move toward Earth when viewed from Earth

• Only thing that wasn’t clear was why some planets sometimes appeared to move in the opposite direction across the sky – (retrograde motion)

RETROGRADE MOTION

• Copernicus (1543 – Polish) suggested that the Sun was the center of the solar system, called heliocentric model

• In the heliocentric model, the faster moving inner planets bypass the outer planets causing the outer planets to appear to move backwards in the sky

• Scientific community thought Copernicus was crazy, until Johannes Kepler, using some of Tycho Brahe’s ideas, demonstrated that the planets move in an ellipse around the sun

• This idea was known as Kepler’s first law

• Ellipse is an oval shape with two foci points instead of a single like a circle – The major axis in a line that intersects the two opposite sides of the ellipse, through the foci points

• Each planet has a different elliptical path, and the sun is always at one focus

• Half the length of the major axis is called the semi-major axis and is the average distance between the Sun and the planet.

• Earth and Sun is 1.496 x 108 km – This distance is referred to as 1 AU (astronomical unit) and is used to measure distances between planets and the sun

• The shape of the planets elliptical orbit is defined by eccentricity, or the ratio of the distance between the foci to the length of the major axis

• Eccentricity ranges between 1 and 0, where 0 is a perfect circle and nearly 1 is a very elongated oval

• Perihelion – when a planet is closest to the sun in its elliptical path

• Aphelion – when it is the furthest from the sun in its elliptical path

[pic]

• Kepler’s Second Law – An imaginary line between the Sun and a planet sweeps out equal amounts of area in equal amounts of time

KEPLER’S SECOND

• Kepler’s Third Law – Relationship between the size of a planet’s ellipse and its orbital period – The square of the orbital period equals the cube of the semi major axis (P2=a3), where P is a unit of time measured in years, and a is a unit of length measured in AU

• Isaac Newton – studied previous works and observed motions of celestial bodies – Led to the law of universal gravitation, which explains how the sun governs the motions of the satellites

- Led to three laws of motion, and the universal gravitation (F = G[m1m2]/r2)

- Where F is force measured in N, G is universal gravitational constant (6.6726 x 10-11 m3/kg/sec2), m are the masses of the objects (kg), and r are the distances between the two bodies (m)

- Determined that each planet orbits a point between it and the sun called the center of mass, or the balance point between two orbiting bodies (see-saw)

29.2 – The Terrestrial Planets

• Terrestrial planets – The four inner planets of our solar system

- Close to the size of Earth and have solid rocky surfaces

- Mercury, Venus, Earth, and Mars (closest to farthest)

• Gas giant planets – last four planets of our solar system

- Larger, more gaseous, and lack solid surfaces

- Jupiter, Saturn, Uranus, and Neptune (Pluto is a planetoid)

• Mercury – Closest to sun

- No moons

- 1/3 the size of the Earth, and has a smaller mass and radius

- 1400 hour day, 2100 day orbit

- Essentially, no atmosphere (oxygen and sodium)

- Day: 427(C/Night: -173(C

- Mariner 10 (1974/75): radio observations

- Craters and plains, formed much like the maria on the moon

- Scarps: fractures formed when Mercury cooled and shrank

- High density suggests nickel-iron core

- Magnetic field of 1% of Earths, suggesting a molten core

- Theory: Crust and mantle ripped away in collision and left core exposed to cool rapidly

• Venus – Next closest to Sun

- No moons

- Brightest planet (0.79 albedo: Highest of planets)

- Planet rotation is 243 days (clockwise, caused by collision early in history)

- Soviet and US spacecraft – 98% of surface by radar

- CO2 and N2 – Concentration (how much per unit volume) vs. Percentage (part of whole)

- CO2 concentration very high – excessive greenhouse effect which cooks the surface of the planet (no escaping radiation)

- Atmosphere of 92 times that of Earth

- Sulfuric Acid clouds

- 464(C – hottest planet

- No craters (atmosphere)

- Relatively young, liquid metal core, no tectonic activity, no magnetic field

• Earth – Next to Venus

- Nearly circular orbit, allow water to exist

- Moderately dense atmosphere, allows for gentle heating of home

- Precession - Earth’s axis wobbles from side to side every 26000 years

- Caused by the sideways pull of the Sun and the Moon (Moon more prominent)

- Will cause seasons to be more extreme when we tilt toward Vega

• Mars – Next to Earth (“Red Planet” caused by iron rich soil)

- Less dense, smaller than Earth

- Two irregularly shaped moons (captured asteroids)

- Much exploration: telescopes and spacecraft

- CO2 and N2 composition – not as concentrated as Venus – Constant wind and dust storms

- Giant volcanoes, lava fields, and canyons that suggest liquid water once was on surface of Mars

- Solid carbon dioxide at poles perhaps cover solid water

- No magnetic field, iron–nickel-sulfur core, with no tectonics

29.3 The Gas Giants

• Cores of solid materials, with fluids, either gaseous or liquid, surrounding them

• Composed of lightweight elements such as hydrogen, helium, carbon, nitrogen and oxygen

• Very cold surface temps

• Very large (15-300 times the size of Earth)

• Jupiter – Largest planet, and 5th from the sun

- 11 times larger than Earth

- Low density due to lightweight elements of composition (H, He)

- Liquid metallic Hydrogen – hydrogen that has properties of both a liquid and a metal due to immense pressure

- Earth size solid core of heavier metals that sunk to core

- Axis rotation of 10 hours making it the shortest day in the solar system

- Belts are low, warm, dark-colored atmospheric clouds, and zones are high, cool, light colored atmospheric clouds (Convection)

- 4 moons of ice and rock, that are heated by gravitational force of Jupiter

- Europa may have seas of water under the surface, possibilities of life? (Water, carbon compound, and heat)

- Faint ring of material surrounding planet

• Saturn – 6th from sun and 2nd largest

- Average density, fast rotation with belts and zones

- H, He, and ammonia

- Similar structure to that of Jupiter, but a magnetic field 1000 times that of Earth

- Rings (7) of rock and ice ranging in size from microscopic to the size of houses

- Rings made up of ringlets and spaces caused by gravitation of moons

- 18 satellites, some with their own atmosphere

• Uranus – 7th from the sun

- 21 moons and rings

- 4 times as large, and 15 times as massive as Earth

- H, He, and methane

- Fluid except a small solid core, with a strong magnetic core

- Rotational axis is tilted so far that the N pole is in orbital plane. Caused by collision.

- 84 year orbit (42 years in darkness and 42 years in light)

• Neptune – Predicted before it was observed from deviations in planetary motions

- 4 times as large as Earth

- Similar composition, atmosphere, and field of Uranus

- Unlike Uranus, distinct clouds, belts and zones

- 8 moons, and 6 rings

• Pluto – 9th planet

- Unique in that it is neither a gas giant nor a terrestrial

- Half ice and half rock

- Methane and Nitrogen

- Extreme eccentric orbit

- Satellite called Charon, which is very close to its own mass

- Same sides face each other at all times

- One theory is that Pluto was once a satellite of Neptune that escaped as a result of a near collision

- Another is a captured comet

OUR SOLAR SYSTEM

SOLAR SYSTEM PERSPECTIVE

29.4 – Formation of Our Solar System

• Stars and planets form from clouds of gas and dust, called interstellar clouds, which exist in space between the stars (H, He)

• Collapse of cloud is slow at first, then accelerates as material coalesces in center

• Cloud eventually becomes a rotating disk with a dense concentration at the center

• As the condensation of the solar nebula continues, the heavier and easier condensing materials formed first closer the hotter center, and the lighter material condensed further away where, it was cooler

• Planetesimals – formations of solid particles during the solar nebula phase into bodies that collided even more to form planets

• Jupiter was the first to condense and it hogged all the dust, gas, and planetesimals, so that none of the other planets became as large

• Accumulation of solar debris also led to satellites

• Refractory compounds (less reactive and stable) were collected by the inner planets, and the more volatile compounds collected by the outer planets where things were much more cool and mellow

• Also, the suns gravitational force sucked in all the gases, and debris, left over around the inner planets (no satellites)

• A asteroid belt between Jupiter and Mars formed because Jupiter’s gravitational field disrupted the condensation process of the material

• Asteroids – leftovers from the formation of the solar system, orbiting the sun in various paths, shapes, and masses

• Meteoroid – any interplanetary material that falls toward the Earth and enters the Earth’s atmosphere

• Meteor – When a meteoroid falls toward the Earth, and burns up in the atmosphere producing a streak of light

• Meteorite – a meteoroid that does not burn up completely and collides with the ground

• Comets – small ice and rock bodies that have highly eccentric orbits around the Sun

- Two origin clouds: 1) Kuiper belt, just past Pluto (50 AU), and 2) Oort cloud, 100,000 AU from Sun

- When the comet comes too close to a hotter stellar object, the ice and frozen gases start to melt, forming head and tails to the comet

- Coma – extended volume of glowing gas around the nucleus, or the small solid core

- The gases from the core form tails that flow away from the sun, due to solar wind

- Meteor shower – When the Earth passes through the tail of a comet. The debris from the comet burn up in the atmosphere, making pretty lights

METEOR DESTRUCTION

PLUTO

METEORS, METEORITES, METEORIODS

METEOR

BILL NYE AND ASTROLOGY

COMETS

KUIPER BELT

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