Today we finished both science and maths. We had already finished the other subjects, as you might have noticed. In science we looked at gravity, the sun and the stars, aswell as day and night and the four seasons.
Gravity is a force that attracts all masses. Gravity gives you weight, but not mass (weight and mass aren’t the same thing).
An object has the same mass whether it’s on Earth, Jupiter, or anywhere else. The weight, however, will change depending on the force of gravity. Weight is measured in newtons, on a spring balance. Mass is measured in kilograms, on a mass balance. So when you say “I way 40 kilos” you’re wrong because 40 kg is your mass, not your weight.
Here is an important formula: Weight (in newtons N) = mass (in kilograms kg) x gravitational field strength (in N/kg).
The Sun is at the centre of our solar system. A planet is something which orbits around a star. E.g the sun is a star, the Earth orbits around it so it’s a planet. The difference between a planet and a star is that stars shine, but planets don’t.
A galaxy is a large collection of stars. The Universe is made up of billions of galaxies. Most of the stars you see at night are in our own galaxy, the Milky Way. There are billions of stars in our galaxy, the Sun is one of them. Other stars include the North Star (or pole star, appears above the north pole) and Proxima Centauri (closest star after the Sun).
A light year is a unit of distance. It is, as you might have guessed, how far light travels in a year. It’s for measuring HUGE distances, like those in space. Proxima Centauri is a bout 4 light years away. That means that you look at it, you’re actually looking at what is what it was 4 years ago. In other words, you’re looking into the past, now that’s cool!
Day and night are due to the steady rotation of the earth. It takes the Earth 24 hours to do a full 360° rotation. That’s what a day is: a a full rotation of the Earth on its axis, which is slightly off set. The seasons are caused by this tilt. The Earth takes 365 1/4 days to orbit around the sun, a year (the extra 1/4 day is sorted out every leap year).
Well, I’m still fascinated by the fact that you can look into the past.