If the substance doesn't change chemically, it is a physical reaction.
-- pushing on a brick wall
-- standing on your little brother's back so that he can't get up
-- taking a nap while on the job
-- squeezing anything that doesn't yield to your squeeze, such as a glass bottle or your girl friend
-- watching TV
-- solving math problems in your head
-- making pictures out of clouds in the sky
<span>The UK government wants to reduce its carbon dioxide emissions. It also wants to increase the amount of energy which comes from renewable sources.</span>
