Motion In The Universe Flashcards
Universe definition
A large collection of billions of galaxies
Galaxy definition
A large collection of billions of stars. Galaxies form due to attractive gravitational forces between the stars.
Solar system definition
The name for the Sun and the objects that orbit around it. Our Solar System is found in the Milky Way galaxy.
Gravitational field strength
Understand why gravitational field strength varies and know that is is different on other planets and the Moon from that on the Earth
The strength of gravity on a planet or moon is called it’s gravitational field strength.
Different planets have different masses. This affects their gravitational field strength
The larger the mass of a planet, the greater it’s gravitational field strength
The larger the radius of a planet, the smaller the gravitational field strength at its surface.
The gravitational field strength on the Earth is 10N/kg
The gravitational field strength on the Moon is 1.6N/kg
Explain that gravitational force causes:
Moons to orbit planets
Causes the planets and comets to orbit the Sun
Causes artificial satellites to orbit the Earth
Isaac Newton suggested his theory of gravity to explain the movements shown in the question card. He said that between any two objects, there is always a force of attraction. This attraction is due to the masses of the objects. He called this force gravitational force.
He suggested that the size of this force depends on the masses of the two objects and the distance between the masses.
It is the gravitational attraction between this mass and each of the planets that hold the Solar System together and causes the planets to follow their curved paths.
Those planets that are closest to the Sun feel the greatest attraction and so follow the most curved paths.
Planets that are the furthest from the Sun feel the weakest pull and follow the least curved path.
Describe the difference in the orbits of comets, moons and planets
All moons have circular orbits because of the gravitational forces between them and their planets.
Satellite definition
An object that orbits a planet
Different types of satellites
There are two types of satellites which are natural and artificial.
Natural satellites are called moons.
Comets
Comets are large rock like pieces of ice that orbit the Sun. they have very elliptical (oval) orbits which at time take them very close to the Sun.
Equation for orbital speed
2pie x orbital radius/ time period
Triangle for orbital speed
Triangle with sectioned four times
2pie in top left, orbital radius in top right, time period in bottom left, orbital speed in bottom right
Example of orbital speed
Calculate the speed of a satellite that is orbiting 200km above the Earth’s surface and completes one orbit in 1 hour and 24mins. The radius of the Earth is 6400km.
Orbital speed - 200km + 6400km = 6600km
Time period - need to turn into seconds
60 + 24 = 84
84 x 60 = 5040
Orbital speed = 2pie x 6600/5040 = 8.2km/s
