Spacetime
9th Grade Science · 6 lessons
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Lessons in this unit
- 1Gravity as a Universal ForceEvery mass attracts every other mass. The force grows with the product of the masses and falls with the square of the distance between them. This one law explains a falling apple, the Moon's orbit and the shape of galaxies alike.Lesson
- 2Orbits Are Continuous Free FallA satellite in orbit is falling all the time; it simply moves sideways fast enough that it keeps missing the Earth. Astronauts float not because gravity is absent — at the space station it is about 90% of its surface value — but because they fall with their craft.Experiment
- 3The Life Cycle of StarsStars form when gravity collapses a nebula until fusion ignites. A star like the Sun spends billions of years on the main sequence, swells into a red giant, then sheds its layers to leave a white dwarf. Much heavier stars end as supernovae, leaving neutron stars or black holes.Lesson
- 4Redshift and the Expanding UniverseLight from distant galaxies is stretched to longer wavelengths, and the further away a galaxy is, the greater the shift. That relationship implies space itself is expanding, which is the strongest evidence for the Big Bang some 13.8 billion years ago.Experiment
- 5Cosmic Microwave Background RadiationThe universe is filled with faint microwave radiation, almost identical in every direction, left over from about 380,000 years after the Big Bang when it first became transparent. Its temperature of 2.7 K and its tiny ripples match the model's predictions closely.Lesson
- 6The Speed of Light as a LimitLight travels at 3 × 10⁸ m/s in a vacuum, and nothing carrying information can exceed it. That finite speed means looking further away is looking further back in time: the Sun you see is eight minutes old, and distant galaxies appear as they were billions of years ago.Lesson
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