1. How & why things go round
Gravity and Orbits
How & why things go round

2. The earth’s orbit …
Earth
Sun
… is an ellipse.

3. Orbits An ellipse is a squashed circle
In the solar system, all the planets have elliptical orbits
The sun in nearly in the centre of these orbits

4. Stars
The Sun is a star
The stars that we see change position in the sky very slowly
They are in fixed patterns – constellations
The planets move more rapidly across the sky

5. Planets and Stars The Sun and other stars give out light
The planets look like stars to the naked eye
Planets reflect light from the sun back to us
Light
Planet
Earth
Sun

6. Comets They have very elliptical orbits
The sun is not at the centre of the orbit
The ‘tail’ of the comet always points away from the sun
Comet and Tail
Orbit
Sun

7. Comets As they get closer to the sun the tail increases in size
They get brighter as the tail reflects more light
They are only visible when close to the sun

8. Gravity
The earth, Sun and moon are attracted by a force called gravity
As the distance between bodies increases, the force of gravity decreases rapidly
Smaller bodies rotate round larger bodies because they move faster and have smaller mass

9. Gravity and centripetal force
Centripetal force in the direction of travel
Gravity – pulls towards the centre