Ancient Greek Astronomers and Mathematicians
Apollonius
Apollonius was a great mathematician who discovered conic sections (curves obtained by cutting a cone with a plane). He also explained the retrograde motion of the planets using epicycles.
Meton
Meton discovered the Metonic cycle (19 years = 235 lunar months) to predict eclipses of the sun and moon, which recur every 19 years. The sun cycle coincides with the moon cycle every 19 years with few exceptions.
Eratosthenes
Eratosthenes discovered the Sieve of Eratosthenes to calculate prime numbers.
Read MoreUnderstanding Electricity, Magnetism, and Electromagnetism
What is Electrical Energy?
Many machines need electrical energy in order to work.
Electrical energy produces changes in matter and can be transformed into other types of energy.
It is transformed into luminous energy in a light bulb.
It is transformed into thermal energy in a vitroceramic hob.
Electrical Charges and Static Electricity
Electricity involves electric charges, which can accumulate in one place or flow from one place to another.
Electric charges can be positive or negative.
Static electricity
Read MoreFundamentals of Astronomy and Physics: Key Concepts
Fundamentals of Astronomy and Physics
4. The frequency of a wave is:
- All of the above
5. You are standing on Earth’s equator. Where is Polaris?
- On the northern horizon
6. Which of the following statements about scientific models is true?
- A model can be used to explain and predict real phenomena.
7. The energy attributed to an object by virtue of its motion:
- Kinetic energy
8. Which of the following statements is NOT true about scientific theories?
- A theory cannot be taken seriously by scientists if it contradicts
Cosmic Evolution: From the Big Bang to Dark Energy
The Future of the Universe
Cosmologists believe that the future of the universe depends on the density of its mass-energy. Two possible scenarios were initially considered: the Big Chill and the Big Crunch. However, the recent discovery of dark energy, responsible for the accelerating expansion, has introduced another possibility: the Big Rip.
- Big Chill: The Great Cooling. An open universe where matter-energy is insufficient to reach critical density, allowing gravity-free expansion.
- Big Crunch: The
Understanding Magnetism: Permanent, Ferro, Para, and Diamagnetic Materials
Understanding Magnetism
Permanent Magnet: Once magnetized, remains magnetized.
Ferromagnet: Easily magnetized (iron, nickel, cobalt, some rare-earth metals, magnetite).
Paramagnet: Magnetized with more difficulty.
Diamagnet: Repels magnetic fields (slightly) – “not magnetic”.
Materials are broken into smaller chunks called “domains”. Each domain has a miniature magnetic field.
Domain Differences
Even if materials look the same, at a smaller level their domains could be different – hence why some
Read MoreThermodynamics: Entropy, Coefficients, and Ideal Gases
Thermodynamics
Entropy
In a Carnot cycle, the integral of Q1/T1 from 0 to Q2/T2 equals 0, where T1 and T2 are the temperatures. This gives us Q1/T1 + Q2/T2 = 0. Considering ΔQ = at, we have at1/T1 + at2/T2 = 0, thus ∑ ΔQ/T = 0.
Now, for a cyclic transformation, ∑ ΔQ/T = ∫1a2 ΔQ/T + ∫2b1 ΔQ/T = 0. If we consider other ways of reasoning, ∫1N2 ΔQ/T, the ratio of heat transfer at different temperatures is a constant. This magnitude is called Entropy.
The third principle of thermodynamics
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