This is a super simple question: does $F$ represent the net force exerted on an object or the force it exerts on another object as a result of momentum? Say a ball is rolling. In this specific instance, if we wrote in equation in the format $F=ma$, would $F$ be the net force acting on it and causing its movement? Or, would F be the force that the ball would exert on another object when it hits it, such as a wall (in this case, I am assuming as mass and acceleration increase, so does momentum, meaning the ball strikes another object with more force)? My teacher was unclear about this, so I am a little confused.
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2$\begingroup$ In $ \vec{a} = \vec{F}_{\textrm{net}}/m$, the acceleration is the acceleration of the obejct, the force is the sum of all the forces acting on the object, and $m$ is the object's mass. This should be clear from your textbook, so consult that too! $\endgroup$– marchCommented Jun 3 at 21:49
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1$\begingroup$ "would F be the force that the ball would exert on another object when it hits it, such as a wall" Why do you think so? Don't make things up yourself. The $F$ in $F=ma$ is the net force. It isn't difficult to find this out. Have you even done any basic research? Please clarify. $\endgroup$– Vincent ThackerCommented Jun 3 at 22:35
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2$\begingroup$ Really don't understand the down votes or closure votes. One would think a new learner to the subject should be encouraged to ask basic conceptual questions here $\endgroup$– RC_23Commented Jun 3 at 22:37
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2$\begingroup$ @RC_23 The question is unclear and lacks basic research. See my comment above. $\endgroup$– Vincent ThackerCommented Jun 3 at 22:38
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2$\begingroup$ "several sources that we have been consulting" Then please include them into your question so that answers can address them. We can't read your mind. Anyway, $F$ in $F=ma$ only has one meaning and that is the net force. This is a fundamental definition in Newtonian mechanics. The entire question of why you think this is unclear and why you think there is some other meaning is beyond me. $\endgroup$– Vincent ThackerCommented Jun 3 at 23:11
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4 Answers
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The acceleration of an object only depends on the forces acting upon that object. Imagine a ball falling down and hitting the floor. There are two forces due to the impact: the force on the ball from the floor, and the force on the floor from the ball. The only force that matters for determing how the ball will move is the first one. The force on the floor due to the ball does not affect the ball.
When using $F=ma$ to study an object, $F$ is the total force on that object, $m$ is the mass of that object, and $a$ is the acceleration of that object. Now, the forces that sum to $F$ on an object may come from other objects (walls, ropes, people pushing), but they only matter for what they do to the object in question.
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$\begingroup$ Of course, the latter of those two forces usually gets neglected because the acceleration on the floor due to a force impressed by a falling ball is usually small (barring an exceptionally large ball). $\endgroup$ Commented Jun 4 at 1:43
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The force in the equation $\vec F = m \vec a$ is the force acting on the body of mass $m$ and whose acceleration is $\vec a$.
It is important to avoid two possible sources of confusion.
- Even though the third principle states that the force of a body $1$ on a body $2$ and the force of a body $2$ on a body $1$ are equal and have opposite directions, the $\vec F$ appearing in the second law is the net force resulting from the vector sum of the forces on the body of mass $m$ due to all the other bodies. As such, if there is more than one body acting on the mass $m$, applying the third principle to the net force $\vec F$ is meaningless
- Some confusion could also originate from the conceptual approach that uses the second law as a force definition. Since $\vec a$ is the acceleration of the body of mass $m$, it could be possible to think that $\vec F$ should also be a quantity associated with the same body, interpreting it as the force exerted on another body. This is not the case, mainly for the same reason as the previous one. .
answered Jun 4 at 6:35
GiorgioP-DoomsdayClockIsAt-90GiorgioP-DoomsdayClockIsAt-90
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The $F$ in Newton’s Second Law is always the force acting on the object undergoing acceleration. What you are describing in the latter half of the post sounds more like a collision to me. https://openstax.org/books/physics/pages/8-3-elastic-and-inelastic-collisions
http://physics.usyd.edu.au/~helenj/Mechanics/PDF/mechanics13.pdf
https://www.astro.uvic.ca/~tatum/classmechs/class5.pdf
Newton’s Second Law doesn’t really come into the picture with collisions. There you are more concerned with conservation of momentum and Kinetic Energy. But perhaps I misunderstood your post. That is my initial take anyway.
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The Newton's 2nd law, $F=ma$, the $F$ is the net force exerted on the object that experiences the acceleration $a$.
The 2nd law only involves one object (or one system). The force and the acceleration that this object (system) experiences, and the mass that this object (system) has.
This law does not tell anything about interaction with other objects (or other systems). For that, you will have to look at Newton's 3rd law of motion.
