Conservation Laws:

• Conservation of Mass: Imagine a closed system, like a sealed container, where nothing goes in and nothing comes out. Regardless of any physical or chemical changes happening inside, the total mass of the contents remains the same. Mass can neither be created nor destroyed in this isolated system.

• Conservation of Energy: Picture a universe without external influences, where the energy is constant. Whether it’s heat, light, motion, or any other form of energy, the total amount stays the same. Energy cannot be created out of thin air or disappear into nothingness within this closed system.

• Conservation of Momentum: In a collision or interaction without any external forces involved, the total momentum remains constant. Think of two billiard balls colliding on a frictionless table; the combined momentum before and after the collision stays the same.

Fundamental Forces:

• Gravitational Force: Imagine two planets in space. The force of attraction between them arises from their masses and the distance between them. The closer they are and the greater their masses, the stronger the gravitational pull. However, as the distance increases, this force weakens.

• Electromagnetic Force: Positively and negatively charged particles have a fascinating relationship. They attract or repel each other depending on their charges and the distance between them. Think of magnets attracting or pushing each other.

• Strong Nuclear Force: At the heart of every atom, protons and neutrons are held together by this super-strong force. It’s what prevents atomic nuclei from breaking apart despite protons’ positive charges trying to repel each other.

• Weak Nuclear Force: This force is involved in certain types of radioactive decay. Compared to the other forces, it’s rather feeble, affecting only subatomic particles at a minuscule level.

Estimation of Distances:

• Parallax Method: Imagine you have one eye closed, observing an object from your left eye, then with your right eye. As the angle changes, you can sense its depth and distance accurately. This technique extends to outer space, where astronomers calculate the distance to nearby stars by observing them from Earth and from spacecraft, using trigonometry.

• Cepheid Variables: Certain pulsating stars, known as Cepheids, have a reliable relationship between their brightness cycle and their true luminosity. By measuring their pulsations, astronomers can determine the actual brightness and compare it to their observed brightness to deduce the distance.

• Supernovae: These colossal stellar explosions are like lighthouses in the cosmos. By carefully measuring the brightness of a supernova, astronomers can calculate its distance using its absolute brightness and the observed brightness.

• Hubble’s Law: Galaxies seem to move away from us the farther they are. This expansion of the universe is governed by Hubble’s Law, which connects the distance of a galaxy to the speed at which it’s receding. By measuring the redshift of a galaxy’s light, astronomers can estimate its distance and trace its cosmic journey.