physics space help

basic questions

Describe the life cycle of a star much more massive than the Sun.

1. Nebula

• A giant cloud of gas and dust in space.

• Gravity pulls the particles together.

2. Protostar

• As gravity increases, the core gets hotter and denser.

• Not yet undergoing fusion, but getting there.

3. Main Sequence Star

• When the core becomes hot enough, hydrogen nuclei fuse to form helium.

• This is nuclear fusion, releasing lots of energy.

• The outward pressure from fusion balances gravity pulling in.

The Sun is currently in this stage – stable and burning hydrogen.

4. Red Giant (for stars like the Sun)

• Hydrogen runs out → core contracts → outer layers expand.

• Star cools and swells into a red giant.

• Helium and other elements start to fuse into heavier ones like carbon and oxygen.

5. Planetary Nebula + White Dwarf

• Outer layers are puffed off, forming a planetary nebula.

• The core stays behind as a white dwarf – very hot and dense, but no more fusion.

• It cools over time and eventually becomes a black dwarf (theoretical, none exist yet because the universe isn't old enough).

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⭐ If the star is much bigger than the Sun… 4. Red Supergiant

• Same idea: fusion of heavier elements like silicon, magnesium, eventually iron.

• Star becomes unstable as fusion stops at iron (because fusing iron doesn’t release energy).

5. Supernova

• The star collapses inwards, then explodes in a huge supernova.

• Heavier elements (up to uranium) are formed during this explosion!

6. Neutron Star or Black Hole

• Core left behind becomes either:

  • A neutron star (if not too massive), or

  • A black hole (if very massive – gravity so strong not even light escapes).

Explain why satellites in lower orbits need to travel at higher speeds than those in higher orbits.

• Satellites in lower orbits are closer to Earth, experiencing a stronger gravitational pull.

• To counteract this stronger pull and remain in orbit, they must travel at higher speeds.

• This ensures the centripetal force required for circular motion is provided by gravity.

What is red-shift, and how does it provide evidence for the expansion of the universe?

• Red-shift refers to the increase in the wavelength of light from distant galaxies, making the light appear more red.

• This occurs because these galaxies are moving away from us, stretching the light waves.

• The observation that most galaxies exhibit red-shift suggests that the universe is expanding, as galaxies are receding from each other.

Describe the Big Bang theory and one piece of evidence supporting it.

The Big Bang theory posits that the universe began from an extremely hot and dense point. One supporting evidence is the cosmic microwave background radiation

"The Moon moves around the Earth at a constant speed, yet it is accelerating. Explain why this is true.

The Moon is moving at a constant speed, but its velocity is changing because its direction is constantly changing as it orbits the Earth.
Since velocity is a vector (it includes both speed and direction), a change in direction means a change in velocity.
Acceleration is defined as the rate of change of velocity, so the Moon is accelerating even though its speed stays the same.
This is because there is a centripetal force (gravity from the Earth) constantly pulling the Moon towards the Earth, causing this continuous change in direction.

Describe how the surface temperature of the Sun will change during its life cycle.

• The Sun is currently a main sequence star, where it is stable and has a high surface temperature due to nuclear fusion of hydrogen into helium.

• As it runs out of hydrogen, the core contracts and the outer layers expand — the Sun becomes a red giant and its surface temperature decreases.

• Later, the outer layers are lost and the core becomes a white dwarf, which is very hot on the surface.

• Over a long period of time, the white dwarf cools down and its surface temperature decreases gradually.