Chp 3: Matter and the Nebular Hypothesis

Question 1

element

Answer 1

An substance that cannot be broken down to anything simpler by chemical means

Question 2

Isotopes

Answer 2

are atoms of the same element that have same no. of protons but different numbers of neutrons

Question 3

Atom

Answer 3

a particle of matter that has the unique properties of an element (i.e., atoms are the essential particles of elements). consists of nucleus(+), in nucleus contains protons(+), neutrons(neutral) and nucleus surrounded by electrons(-)

Question 4

Ion

Answer 4

• an atom with either a negative charge (i.e., it has extra electrons)
• or an atom with a positive charge (i.e. it has a deficiency of electrons).

Question 5

Nebular Hypothesis (short ver)

Answer 5

-the Big Bang created matter, that the most basic forms of this matter combined to form elements, and that eventually pockets of matter/elements combined to form star-planet systems.

Question 6

Radioactivity

Answer 6

the spontaneous break down of unstable atoms (i.e., unstable isotopes) of an element, with the production of energy and other particles.

Question 7

Fission

Answer 7

a breakdown of the nucleus of a relatively heavy atom (i.e., isotope) into at least two other lighter particles plus energy.

Question 8

Fusion

Answer 8

the combination of two lighter atoms/isotopes to make one heavier atom/isotope plus energy.

Question 9

Supernova

Answer 9

the explosive death of a massive star.

- While the explosion is virtually instantaneous, the bright effect can sometimes be seen for weeks, both day and night

Question 10

Formation of elements from light to heavy. Which ones form in the big bang, a star or a supernova?

Answer 10

• As the cloud of cosmic dust and gases from the Big Bang cooled, stars formed, and these then grouped together to form galaxies.
• The Big Bang created hydrogen (H), helium (He) and lithium (Li). The other elements found in nature were created in nuclear fusion reaction in stars and also in huge stellar explosions known as supernovae.

Question 11

Describe the nebular hypothesis for the formation of our solar system.

Answer 11

• this enormous (but very low-density) gas cloud, spread out over a very large volume of space
• contracted under its self-gravity (i.e., all the particles were attracted together by the cumulative gravitational effects of all the other particles in the cloud).
• There was a pronounced shrinkage and flattening of the original cloud.
• gravity pulls in the mass of the nebula in, then starts spinning, then the disk forms (planetary, solar disk)
• gravitational energy gets converted to thermal energy (heat); gets so hot, then nuclear fusion, then the sun is born
• disk cools and masses clump together
• masses (planets) increase and orbits (clears neighborhood), and becomes more defined
• Planets differentiate and layers form
• Planets grow by accretion

Question 12

Collapse Process (Nebular Hypothesis)

Answer 12

• at first, a pocket of the cloud began to contract, the collapsed region increased in density when the contraction started
• atoms, once comfortably separated, were banging about vigorously, generating heat in the process. Once it started, there was a local collapse to that part of the cloud.
• Once that started, the collapse would have accelerated, going faster and faster.
• As the particles got closer together, they collided more and more frequently. the particles become so densely packed that the heat can no longer escape.
• Any thermal energy (radiation) that is emitted from the hot central regions would be blocked by the surrounding dense layers of matter.
• The heat is trapped, and builds up. At this stage, the particles near the centre wind up moving at very high speeds (i.e., the gas is very hot), which means that they can provide enough sustaining pressure to stop any further collapse.
• The great heat of the gas now means that fusion reactions can take place. This releases yet more energy, and a star is born.

Question 13

Why is the Sun hot?

Answer 13

• The Sun converts hydrogen nuclei into helium nuclei.
• These fusion reactions convert part of the mass of these atoms (roughly 4 million tons) into energy, and release an enormous amount of heat and light energy into the Solar System.

Question 14

Why is the solar system a flat disc?

Answer 14

conservation of angular momentum.
-the original cloud would some have some circulation or motion of gas inside it. when all these motions are added up there is likely to be some slight cumulative motion in some direction. This defines the ‘sense of rotation’ of the cloud, as well as its angular momentum.
-Given this slight original rotation, it is inevitable that the cloud will spin faster and faster, with this sense of rotation, as it contracts.
-The increasingly rapid spin of
orbiting material leads to its flattening out.

Question 15

Momentum

Answer 15

a measure of an object’s tendency to move at constant speed along a straight path (when you apply the brakes of your car, you are reducing its momentum).

Question 16

Angular momentum

Answer 16

a measure of the amount of spin (or orbital motion) of an object

Question 17

Conservation of angular momentum

Answer 17

If no outside force acts on a spinning (or orbiting) object, the object’s angular momentum will not change with time, no matter how the object interacts with other objects

Question 18

the flattened nebula has a _______ _______: although it was very hot at the center, it was cool farther out.

Answer 18

temperature gradient

Question 19

dew point temperature

Answer 19

dew point: temperature to which air must be cooled to reach water saturation, after which water molecules begin to form

Question 20

refractory elements

Answer 20

elements that do not readily respond to

heat) could condense (and freeze)

Question 21

Why did all planets originally move in the same direction around the Sun?

Answer 21

• the reason the pebbles were all going in the same direction is because during flattening, due to conservation of momentum, although atoms can be moving in different ways, when all these motions are added up, there is some cumulative motion in some direction.
• So originally, the atoms were cumulatively going in the same direction as well.

Question 22

Accretion

Answer 22

sticking together (lumps of pebbles)

Question 23

The interior planets are made from condensed refractory materials, what happened to the more volatile gases?

Answer 23

• The lighter gases (in the inner part of the solar system) are unable to condense, only the heavier refractory elements can condense and eventually form planets.
• many of them condense farther from the sun (where it is cool enough) and form the giant gas planets, like Jupiter.

Question 24

What is the solar wind?

Answer 24

a continuous outflow of charged particles (mostly electrons) that stream out through the Solar System at a velocity of several hundred kilometres per second

Question 25

If we want to see what the Sun would have looked like at its formation, we can look at

Answer 25

T Tauri Stars

Question 26

The reason there are usually more clouds in the sky rather than on the ground is because

Answer 26

The temperature is cooler higher in the atmosphere

Question 27

Explain how changes in bombardment rates support the nebular hypothesis

Answer 27

• The bombardment rate refers to the number of collisions.
• Early in the formation process, there would have been a large amount of small collisions; whereas later, there would have been a fewer number of collisions with larger masses.
• This was found to be true from the evidence of the craters on the moon. The large clumps in the formation later on would result in very large collisions.
• Together, this shows the process of the Solar System forming as a unit due to the process of accretion.

Question 28

How will our solar system likely be destroyed?

Answer 28

• Our sun will run out of hydrogen fuel in about 5 billion years. This will then result in the sun expanding into a red giant which will wipe out and destroy our solar system.
• Andromeda is also expected to collide with the Milky Way in about 3 billion years!