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--- 183_notes:acceleration [2014/07/10 20:51] – caballero
+++ 183_notes:acceleration [2021/02/04 23:19] – [Newton's Second Law] stumptyl
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 ==== Newton's Second Law ====
-The Momentum Principle (or Newton's Second Law) is a quantitative description for how a system changes it momentum when the system experiences an external force. You might already know that another way to write this principle uses the concept of acceleration (how the velocity changes with time). Mathematically, we can write Newton's Second Law like this:
+The Momentum Principle (or Newton's Second Law) is a quantitative description for how a system changes its momentum when the system experiences an external force. You might already know that another way to write this principle uses the concept of acceleration (how the velocity changes with time). Mathematically, we can write Newton's Second Law like this:
 $$\vec{F}_{net} = m\:\vec{a} = \dfrac{\Delta\vec{p}}{\Delta t}$$
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 $$\vec{a} = \dfrac{\Delta\vec{p}}{m\:\Delta t}=\dfrac{m\Delta\vec{v}}{m\:\Delta t}=\dfrac{\Delta\vec{v}}{\Delta t}$$
-where the last two equals signs hold only if the mass of the system is not changing.
+__//where the last two equals signs hold only if the mass of the system is not changing.
+//__
 ==== Acceleration ====
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 The units of acceleration are meters per second per second ($\dfrac{m}{s^2}$).
+==== Why not just use change in momentum? ====
+If you have one way of describing motion (i.e., using the concept of a change in momentum), why should you learn about acceleration?
+Acceleration is a useful concept in mechanics, because it can help characterize the motion of systems (e.g., constant velocity motion has no acceleration).
+While you can obtain this information by determining the forces acting on the system, it's possible to use observational information (how the position changes) to determine how the system is accelerating without knowing the system's mass or the forces acting on the system. This is incredibly useful for any type of data collection. Any data collected about the motion of a system only records the position of the system as function of time. From the changes in position (displacement), the velocity can be inferred. From the changes in the velocity, the acceleration can be inferred and thus the motion of the system can be characterized and explained.