The correct answer is resistance, which is defined as an external force that acts against movement, such as friction or air resistance. Other options like gravity, efficiency, and momentum do not fit this description. Understanding resistance is crucial in the study of physics as it affects motion significantly. ;
The correct answer is resistance, which is an external force that opposes movement. Examples include friction, air resistance, and water resistance. Understanding these forces is essential in physics as they affect how objects move.
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