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Q & A: rockets changing direction

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Most recent answer: 10/22/2007
Q:
If there is no propulsion is space, how does a rocket turn in mid-flight?
- Richard (age 27)
London
A:
I'm not sure where you heard that there's no propulsion in space. You're right that without some force on them, rockets couldn't turn directions. But even in space, there is a force (propulsion) on a rocket. It's the force between the rocket and whatever its exhaust is- typically some sort of gas. If the rocket changes direction a little, you know that the exhaust must be expelled in a direct opposite to that change. That's because Newton's third law says that the force the rocket exerts on the exhaust is opposite to the force the exhaust exerts on the rocket. Another way of putting that is that momentum is conserved.

Mike

(published on 10/22/2007)

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