1What affects the gravitational field strength on a planet’s surface?
Mass
The greater the mass of a planet, the greater the gravitational field strength (g)
2 Why will an object not have the same weight on earth and on the moon?
Earth has a greater mass, so its gravitational field strength (g) is stronger
Since W=mg
the object will weigh more on Earth
3 What is at the centre of the Solar System?
The Sun (a star)
4How many planets are in the Solar System?
Eight
5What are the four planets closest to the Sun called (collectively and in order)?
Inner planets
Mercury, Venus, Earth, Mars
6 Features of inner planets
Small and rocky - high density
7What are the four planets furthest from the Sun called (collectively and in order)?
Outer planets
Jupiter, Saturn, Uranus, Neptune
8Features of outer planets
Large and gaseous - low density
9What is found between Mars and Jupiter?
The Asteroid belt
10Features of an asteroid
Small and non-spherical
(Near) Circular orbit around the sun
Made from rock (similar density to inner planets)
Found in the asteroid belt (between Mars and Jupiter)
11Features of a comet
Small and non-spherical
Highly elliptical orbit around the sun
Made from ice and dust (similar density to outer planets)
Can be found beyond Neptune
12Definition of a satellite
Any object that orbits around a planet (like moons)
13 What do moons orbit?
Planets
14 Difference between artificial and natural satellites
Artificial satellites are man-made (like the ISS)
Natural satellites are not man-made (like the moon)
15 Features of a planet
(Near) Circular orbit around the sun
Large enough to be spherical
Large enough to clear smaller objects from its path
16 Features of a dwarf planet
(Near) Circular orbit around the sun
Large enough to be spherical
But not large enough to clear smaller objects from its path
17Describe the geocentric model
Ancient model
With Earth at the centre of the solar system
18Describe the heliocentric model
Accepted model
With the sun at the centre of the solar system
19Evidence supporting geocentric model
Sun, moon and stars move across the sky
and look like they are going around the Earth, not the sun
From simple observation, they appear to move in same direction and in the same pattern each day
20Evidence against geocentric model
Moons can be seen orbiting other planets, not the Earth
From careful observation, movements of Sun and other objects is not the same each day
Telescope observations show planets do not move in a simple orbital path around the earth
21Before the invention of the telescope…
It was difficult to make detailed observations about the solar system
So ideas were based on what could be seen with the naked eye
22 What is the force that causes objects to orbit eachother?
Gravitational force
23 Similarities between orbits of different planets
Slightly elliptical orbits (even if near circular)
All orbit in the same plane
All travel in the same direction around the Sun
24Differences between orbits of different planets
Orbit at different distances from the Sun
Orbit at different speeds
Take different amounts of time to orbit the Sun
25 Planets further from the sun…
Travel at slower speeds
Take more time to orbit
26 Planets closest to the sun…
Travel at faster speeds
Take less time to orbit
27 What shapes are the orbits of moons?
(Near) Circular
28 Moons closer to a planet…
Travel at faster speeds
Take less time to orbit
29 Moons further from a planet…
Travel at slower speeds
Take more time to orbit
30Describe the orbit of a comet
Comets have highly elliptical orbits (very stretched)
When they are close to the sun, their speed increases
As they move away, their speed decreases
31 Describe the velocity of an object moving in a circular orbit at a constant speed
Speed is constant but velocity is constantly changing - direction is changing.
32What is the force that causes circular motion or orbiting?
Centripetal force that acts towards the centre of the circle
33 Is the moon orbiting the Earth at a constant speed an example of Newton’s first law?
No! The moon is constantly changing direction
so velocity is changing/not constant
There is a centripetal force (gravity).
34Name the centripetal force which acts when a satellite orbits a planet
Gravitational force
35Why is an object in (near) circular orbit said to be accelerating?
F=ma
If there is a resultant force there is acceleration
The gravitational force is the resultant force
And since the velocity is changing (because the direction is changing) the planet is accelerating
Even though the speed is constant
36 What is meant by a stable orbit?
When an object moves around a larger body in a predictable way
Path does not change over time
Can be circular or elliptical
37Features of a (near) circular orbit
Sun is at the centre
Orbital speed is constant
38Features of an elliptical orbit
Sun is not at the centre
Orbital speed increases near the Sun
Orbital speed decreases far from the Sun
39 In a stable orbit, what happens if the radius changes?
If the radius decreases, speed increases
If the radius increases, speed decreases
40In a stable orbit, what does it mean if the speed changes?
If the speed decreases, radius is increasing
If the speed increases, radius is decreasing
41 Energy transfers for a comet approaching the sun
The radius decreases, but velocity increases
Energy is transferred from the gravitational potential store to the kinetic store
42Energy transfers for a comet travelling away from the Sun
The radius increases, but velocity decreases
Energy is transferred from the kinetic store to the gravitational potential store