Momentum and Energy


What plays the role of force in rotation?

You have had experiences that illustrate how torque works. Suppose you want to push open a door that rotates about its hinges. You know that the speed with which the door opens depends on how hard you push. It also depends on how far from the hinges you push—the farther the faster. It also depends on the angle at which you push. Pushing at a right angle to the door is much more effective than pushing at a smaller or larger angle. If you push at a right angle, then torque equals the force times the distance from the axis of rotation.

With nothing to technically “push against” in space, it seems odd that rockets could accelerate in space. The explanation is that the force of the combusting rocket fuel itself pushes the rocket, accelerating it forward.

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