Concepts of Planar Kinematics of a Rigid Body

[cs23]

I've always heard my profs say, you must understand the concepts rather than just memorizing how to solve a group of problems.

lets say I'm reading a chapter on Planar Kinematics of a Rigid Body. Are the different sections the concepts?

 

[JHamm]

A concept is a broad idea, things like energy and momentum conservation, Newton's laws, how work and energy go together. He's emphasising that you need to learn to understand what is going on rather than just learning the steps to solving a "projectile motion" problem or a "circular motion" problem.

 

[Mike706]

"You do not really understand something unless you can explain it to your
grandmother." - Albert Einstein

Basically, he's saying you should strive to be able to do this. You learn a lot by explaining things to people. Not that you need to go preaching physics to people, but you should be able to describe in words (your own words, not memorized words from the text) what is going on. Try it for yourself - write a paragraph about planar kinematics (or whatever the topic is). If you can do that, and do it in a way that someone who isn't familiar with the subject could read what you wrote and understand the basics of what's going on, then you understand the concepts.

Edit - good question.

 

[cs23]

A concept is a broad idea, things like energy and momentum conservation, Newton's laws, how work and energy go together. He's emphasising that you need to learn to understand what is going on rather than just learning the steps to solving a "projectile motion" problem or a "circular motion" problem.

Would you say that the concept is not necessarily the equations.(i don't know if that made sense).Basically, you can describe something without having to refer to the equations. For example, the concept of torque can be explained generally without having to go into specifics(i.e equation).

I think what separates us from everyone else, is that any average joe can take an equation and solve a problem. But to explain the concept without the equation is the difference

 

[physics girl phd]

I'll also note that understanding concepts will allow you to develop reasonable models or sets of equation... and analyze the results of data collection and/or any calculations you have done to see if they make sense.

Example: One of my favorite questions in undergraduate physics was a quantum mechanics problem (from Griffiths) that I believe asked you to find the average statistical position for a "particle" in a "box" and noted for you to "go directly to jail" if your calculation gave a position outside the box. Obviously, the calculation should also place the particle in the middle of the box... or you set up boundaries of the box, applied boundary conditions wrong, etc. -- you'd be surprised, but students still miss the question and don't even understand the author's comment/joke.

 

[cs23]

So is the concept the idea rather than the equation. If someone asked me to explain torque, would the concept be "a twisting force" rather than regurgitating the formula (t=fd)? The equation just allows to calculate things,right?

 

[mal4mac]

Concept is a pretty vague concept :)

For instance my dictionary of philosophy has various definitions depending on the context - in the weakest definition just being able to say "sheep" in the presence of sheep means you have a grasp of the concept "sheep".

In an example problem you might be shown how to calculate t given f and d, using t = fd. If you just plug in the numbers you can get the magnitude of t, but may have no grasp of the most basic idea that t is a twisting force. So your professors, I guess, would say that you then have no understanding of the concept of torque at all, in any real sense, even if you can plug and chug some questions.

Just knowing that "t is a twisting force" is not enough - a physicist needs a stronger grasp of the concept of torque. Just knowing that t = fd is not enough. But put the two together and you grasp the concept in a stronger way.

If you can explicitly give the *exact* direction of "twist" you then understand the concept in an even stronger way... and you can keep on going, adding levels of explanation.

Interesting question - can you ever fully understand any concept?

 

[mal4mac]

... write a paragraph about planar kinematics (or whatever the topic is). If you can do that, and do it in a way that someone who isn't familiar with the subject could read what you wrote and understand the basics of what's going on, then you understand the concepts.

If you can do this, you have shown you "understand the concept" in the weakest way. But to show you "really" understand the concept you need to show you can solve problems as well.

 

[Choppy]

I agree largely with what Mal4mac has said.

Understanding a concept also means understanding the context in which it applies and it's limits.

In my opinion, one of the best exercises a physics student can do is apply concepts covered in class to external scenarios.

Going back to the example of torque. Do you understand why torque has a direction? Do you understand why that direction is different from that of the applied force? Do you understand why on your bicycle it is easier to pedal when you're in a gear that uses a larger sproket on the back wheel than a smaller one? Or why the opposite is true on the front sproket? Could you exert a torque on an electron? How might you go about doing that?