Combined Science
Physics
Cambridge IGCSE
Physics
Cambridge IGCSE
TOPIC 6: SPACE PHYSICS
Have you ever wondered about the vastness of space? How many stars might exist in the universe? Scientists believe that while the universe has an observable size limit - one that is difficult to comprehend - it is astonishingly immense.
One of the best ways to visualize this is through an animation that takes you on a journey from Earth to the farthest reaches of what we can observe. This captivating video not only provides perspective but also introduces several key concepts:
YouTube video: The size of the universe
Cosmic Voyage - The US National Air and Space Museum
In this topic on Space Physics, we will learn about all astronomical objects, from the Earth out to the edge of the known Universe.
Our Solar System consists of 8 planets that orbit a central star - the Sun. You should have met this topic before and you may well have a good grasp of the structure of the Solar System already. For this course, you should be able to name the planets in order.
The four planets nearest the Sun are rocky and small, including the Earth, and the four planets furthest from the Sun are gaseous and large.
Figure 1: The planets in our Solar System
Distances not to scale!
WP | CC BY-SA 3.0 via Wikimedia Commons
In addition to the 8 planets, there are also many minor 'dwarf' planets that orbit the Sun. These are smaller objects that could - at some stage - collide with other objects such as the major planets. For this reason, Pluto is now classified as a dwarf planet as it could, at some stage in the future, collide with the much larger planet Neptune.
Moons orbit most of the planets. We only have 1 large moon, but this number varies widely. For example, Jupiter has 79 known moons at the time of writing.
In addition, there are smaller Solar System bodies, including comets which characteristically have highly elliptical orbits (see below), and other natural satellites.
In between Mars and Jupiter lies the asteroid belt. This is a ring of various sizes of rocky objects, some that are so large to be classed as minor (dwarf) planets (e.g. Ceres and Vesta.) Instead of gravity pulling these rocks together to form another rocky planet, it is believed that Jupiter's strong gravitational influence broke up any small planets and prevented their formation, leaving a large ring of rocky asteroids.
Figure 2: The asteroid belt (shown by black dots between the orbits of Mars and Jupiter)
NASA/McREL
The motion of galaxies, stars and planets are all ruled by the force of gravity. This force between any 2 objects depends on the masses of the objects and also the distance between them. The pull of gravity makes:
(An orbit is the path taken by an astronomical object as it moves around another).
In section 1.3 we met the concept of gravitational field strength (g). On Earth, this is always about 9.8 N/kg, but varies on other planets. For example, on the surface of Mars, g= 3.7 N/kg. This is much lower than on Earth because Mars has a much lower mass than Earth.
The further you move away from a massive object like a star or a planet, the weaker the gravitational field strength becomes. On the Earth's surface, g=9.8 N/kg, but if we could stand on a stationary platform 6000 km above the Earth's surface, the value of g would only be 2.6 N/kg. We would feel only about ¼ of our normal weight, and could jump 4 times higher!
The Sun contains most of the mass of the entire Solar System. This is why the Sun stays in the centre of our Solar System whilst the force of gravity makes the planets orbit around it.
Questions:
1. State the name of a planet in our solar system that is:
2. Choose words from the list below to complete this sentence:
Mars orbits the Sun in a near circular path because of the force of ____________ from ________.
Mars orbits the Sun in a near circular path because of the force of gravity from the Sun.
For this double science course, we can now move on to learning about stars, including our own start, The Sun.
Here's a quick 10 minute quiz about the Solar System:
