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 inertia is the energy by which you keep moving. like if you bike  like you go down a hill and you keep going that is inertia. kicking in it more or less makes you move but their are things that stop it like friction. would be one when you go down a hill if their are little humps of grass or something this would slow your energy down. and if you had a enough you would stop like we did a project a while back where i had to roll a toy car over some rough surfaces. and we would see wat kind of friction it is like carpet had like tons of friction. also a rug or like just the tile on your kitchen would have inertia and  friction the friction works against inertia.