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I felt pretty comfortable with forces being m*a, and it made sense that friction was a force, and so many of these other naturally ocurring things had constant forces occurring, until my class got to kinetic energy. Now I am confused as to why constant forces are acting so commonly as opposed to constant energy gain / loss, since energy seems to be what everything runs on, and it is quadratic to v rather than linear to v. Where as forces are linear. If someone could help me with this that would be greatly appreciated

Qmechanic
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user180969
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  • What do you mean by "constant force"? Constant in what sense? Also why do you think forces are linear in $v$? – user1583209 Jan 16 '18 at 21:32
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    There are multiple different questions mingled up in here (it seems to me). The question about why kinetic energy is quadratic in velocity is covered here: https://physics.stackexchange.com/q/535/ - however, the explanation is necessarily nontrivial – Martin Jan 16 '18 at 21:37

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"I felt pretty comfortable with forces being m*a, and it made sense that friction was a force, and so many of these other naturally ocurring things had constant forces occurring, until my class got to kinetic energy. Now I am confused as to why constant forces are acting so commonly as opposed to constant energy gain / loss, since energy seems to be what everything runs on..."

I don't think this really has much to do with the way the physical world works. It more has to do with the method they choose to teach you.

It's a lot easier to solve problems with constant force than it is with varying force. This is why, when forces are introduced with physics, we choose to start with examples of constant force.

In general, most objects experience forces that vary over time. Some forces are far closer to constant (under the right conditions) than others. Common examples used for introductory physics include things like weight and Coulomb friction.

Energy isn't constant either (although in theory, total energy is constant in a closed system). Energy is constantly going between different forms and acting on different systems.

Basically, in any non-simplified analysis, both forces and energy can vary over time in an open systems. It's merely a teaching tool in physics to focus on constant forces instead of variable forces at first. A constant acceleration is a lot easier to work with than a constantly changing acceleration.

JMac
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