Friends Parts I World Earth Ball Shaped Object Live

earth/Earth = the ball-shaped object that we live on, usually seen as a planet in space: 'The earth moves round the sun every 365 days.' 'On the journey back to Earth, one of the spaceship's computers failed.'

world = the ball-shaped object that we live on, usually seen in terms of people, countries, cities etc: 'Tuberculosis is still common in some parts of the world.' 'It's one of the largest countries in the world.' 'You'll be seeing some of the world's leading golfers.'

Note the expression all over the world (= everywhere in the world): 'I have friends all over the world.'

planet = the ball-shaped object that we live on, usually seen in terms of the natural environment: 'This disaster could affect the whole planet.' 'The planet is gradually getting warmer.'