- #1

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## Main Question or Discussion Point

I just started Physics 1 this semester. Although the kinematics we covered so far were simple, our teacher didn't do a particularly good job at explaining dynamics. In fact, all 10 students I talked to were left clueless by his lecture.

What we don't understand at this point is the concept of F=ma. Here are a couple examples of the concepts I and the other students don't understand:

1) Say I am pushing a table across the floor at a constant velocity. Since the velocity is constant, acceleration would be 0 (please correct me if I am wrong), which means that F=0. However, as soon as I stop applying force to the table, the table stops moving, so clearly I am applying some type of "force" on it while I am pushing it. So, if what I am doing is not considered force because there was no acceleration involved while pushing it at a constant velocity, what would it be, and how do you differentiate between what I am doing and a force?

2) From our text (Spiral Physics), it states that if you are holding onto a rope, the force of gravity pulling you down is equal to the force of the rope pulling you up. That concept I get. However, it also states that if you are climbing the rope, the two forces (gravity and the rope) are still equal? This has me very confused, as it takes far more energy to pull yourself up the rope than to hold you in place. In addition, I know each time you move upward, you are exerting more of some type of "force" on the rope than if you were stationary. So, can someone please explain what is wrong with my perspective that is keeping me from understanding this?

If someone could answer those two questions, me and my classmates would greatly appreciate it. If there are any decent resources to self-teach this stuff, that would be great as well, as our instructor just isn't explaining this stuff in a way that makes sense. From what I've heard from other students, it just gets worse as the semester goes on.

What we don't understand at this point is the concept of F=ma. Here are a couple examples of the concepts I and the other students don't understand:

1) Say I am pushing a table across the floor at a constant velocity. Since the velocity is constant, acceleration would be 0 (please correct me if I am wrong), which means that F=0. However, as soon as I stop applying force to the table, the table stops moving, so clearly I am applying some type of "force" on it while I am pushing it. So, if what I am doing is not considered force because there was no acceleration involved while pushing it at a constant velocity, what would it be, and how do you differentiate between what I am doing and a force?

2) From our text (Spiral Physics), it states that if you are holding onto a rope, the force of gravity pulling you down is equal to the force of the rope pulling you up. That concept I get. However, it also states that if you are climbing the rope, the two forces (gravity and the rope) are still equal? This has me very confused, as it takes far more energy to pull yourself up the rope than to hold you in place. In addition, I know each time you move upward, you are exerting more of some type of "force" on the rope than if you were stationary. So, can someone please explain what is wrong with my perspective that is keeping me from understanding this?

If someone could answer those two questions, me and my classmates would greatly appreciate it. If there are any decent resources to self-teach this stuff, that would be great as well, as our instructor just isn't explaining this stuff in a way that makes sense. From what I've heard from other students, it just gets worse as the semester goes on.