Blow up means to explode or to destroy something with an explosion, and also to fill something with air (a balloon, a mattress, a pillow). The car blew up means that the car exploded. To blow up a balloon is to fill it with air, by mouth or with a pump.
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something blows up; blow up + a bridge / a car; blow up + a balloon / a mattress
- Firefighters moved everyone away from the burning car in case it blew up.
- Demolition experts blew up the old cooling towers to make room for new housing.
- Before the long flight, I blew up my travel pillow so I could sleep on the plane.
What changed
First versionWe blew fifty balloons for my daughter's birthday.
RevisionWe blew up fifty balloons for my daughter's birthday.
“Blow” without “up” simply means to push air out of your mouth, so the sentence says that you blew at fifty balloons. To fill a balloon with air, you need “blow up”, which is why “up” was added in the corrected sentence.
“Explode” is usually used about the thing that explodes: The bomb exploded. To say that someone destroyed a bridge, a car or a building with explosives, use “blow up”: They blew up the bridge. “They exploded the bridge” sounds unnatural.
Your turn
We forgot the pump, so we had to ___ the air mattress by mouth.
Show the answer
blow up — You fill a mattress with air, so you blow it up: “blow up”. “Blow out” means to put out a flame by blowing, as with the candles on a cake or a match.
Think of a film or series in which something was blown up. Say what was blown up and why.
In the last episode, the rebels blew up a bridge to stop the army from crossing the river.
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