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Complete the following: The rate of change in what with respect to time is equal to the acting force.
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Let’s define the acting force to be equal to 𝐹.
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One of the expressions we have that links force with the rate of change of some quantity is force is equal to d by d𝑡 of 𝑚𝑣.
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In other words, force is equal to the rate of change of mass times velocity with respect to time.
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But what do we know about this expression mass times velocity?
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Well, we know that momentum is equal to mass times velocity.
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This means that we can alternatively express force as the derivative of momentum with respect to time.
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So, the rate of change in momentum with respect to time is equal to the acting force.
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And so, the missing word here is momentum.