Quick Q's (1 Viewer)

[axwe7]

If momentum (a vector) is conserved, explain why, after a ball bounces off a wall or the ground, the direction of the momentum vector has changed.

2. How would you explain the bouncing of a ball, Newton's 3rd Law? Because that's an equal & opp. therefore wouldn't it just keep going at a constant velocity?

 

[porcupinetree]

If momentum (a vector) is conserved, explain why, after a ball bounces off a wall or the ground, the direction of the momentum vector has changed.

The Law of Conservation of Momentum is as follows:
"The total momentum of a system is conserves if no external net force acts upon the system."

In your example, it seems to me that you specify the ball as the system in question. If no external forces acted on the ball, then we would expect its momentum to be conserved. However, if it bounces off a wall/ground, it experiences a force from the wall/ground, hence the Law of Conservation of Momentum does not apply.

(A better question would be to ask, "ok, but what if we let the system include both the ball AND the wall? No net force acts on the system, so momentum should be conserved, shouldn't it?"

In fact, a net force DOES act on the system: some kind of friction/normal force from the wall being connected somehow to the ground.)

2. How would you explain the bouncing of a ball, Newton's 3rd Law? Because that's an equal & opp. therefore wouldn't it just keep going at a constant velocity?

A common misconception is that in an action-reaction pair of forces, the forces act on the same object. This is wrong. In an action-reaction pair, each force (which is equal and opposite to the othet) acts on a DIFFERENT object. In the ball bouncing scenario, the ground will apply a normal force TO THE BALL, causing the ball to accelerate upwards. The ball will apply an equal and opposite force TO THE GROUND.

 

[eyeseeyou]

The Law of Conservation of Momentum is as follows:
"The total momentum of a system is conserves if no external net force acts upon the system."

In your example, it seems to me that you specify the ball as the system in question. If no external forces acted on the ball, then we would expect its momentum to be conserved. However, if it bounces off a wall/ground, it experiences a force from the wall/ground, hence the Law of Conservation of Momentum does not apply.

(A better question would be to ask, "ok, but what if we let the system include both the ball AND the wall? No net force acts on the system, so momentum should be conserved, shouldn't it?"

In fact, a net force DOES act on the system: some kind of friction/normal force from the wall being connected somehow to the ground.)



A common misconception is that in an action-reaction pair of forces, the forces act on the same object. This is wrong. In an action-reaction pair, each force (which is equal and opposite to the othet) acts on a DIFFERENT object. In the ball bouncing scenario, the ground will apply a normal force TO THE BALL, causing the ball to accelerate upwards. The ball will apply an equal and opposite force TO THE GROUND.

Why?

 

[eyeseeyou]

The Law of Conservation of Momentum is as follows:
"The total momentum of a system is conserves if no external net force acts upon the system."

In your example, it seems to me that you specify the ball as the system in question. If no external forces acted on the ball, then we would expect its momentum to be conserved. However, if it bounces off a wall/ground, it experiences a force from the wall/ground, hence the Law of Conservation of Momentum does not apply.

(A better question would be to ask, "ok, but what if we let the system include both the ball AND the wall? No net force acts on the system, so momentum should be conserved, shouldn't it?"

In fact, a net force DOES act on the system: some kind of friction/normal force from the wall being connected somehow to the ground.)



A common misconception is that in an action-reaction pair of forces, the forces act on the same object. This is wrong. In an action-reaction pair, each force (which is equal and opposite to the othet) acts on a DIFFERENT object. In the ball bouncing scenario, the ground will apply a normal force TO THE BALL, causing the ball to accelerate upwards. The ball will apply an equal and opposite force TO THE GROUND.

Why

 

[leehuan]

Why?

When there's no force, velocity is constant. p=mv so momentum is constant as well (mass can't change is assumed).

Bouncing off a wall - experiencing a force. But the ball DOES NOT feel itself exerting a force onto the wall. The ball feels the WALL exerting the EQUAL and OPPOSITE force back onto it.

 

[InteGrand]

Why?

Because of the Law of Conservation of Momentum (and Newton's Third Law).

Why

Because of Newton's Third Law.

 

[porcupinetree]

Why?

Specifically, the ball experiences a force when it comes into contact with the wall because of electrostatic interactions between the ball's atoms and the wall's atoms.

 

[porcupinetree]

Why

Again, normal forces such as this occur because of electrostatic interactions on the atomic scale. The ball accelerates upwards as is described by Newton's 2nd Law F=ma (i.e. a force causes an acceleration in the direction of the force). Then, by Newton's third law, the ball will apply an equal and opposite force to the ground (in the same way that we consider the ground's atoms to exert an electrostatic force on the ball's atoms, we can consider the ball's atoms to exert an equal force on the ground's atoms).

 

[eyeseeyou]

Specifically, the ball experiences a force when it comes into contact with the wall because of electrostatic interactions between the ball's atoms and the wall's atoms.

What causes the electrostatic interactions between the ball's atoms and the wall's atom?

 

[porcupinetree]

What causes the electrostatic interactions between the ball's atoms and the wall's atom?

The constituents of atoms (ie nuclei & electrons) are charged; the interactions of these charges leads to electrostatic forces in accordance with Coulomb's Law. (ie like charges repel, opposites attract)

 

[eyeseeyou]

The constituents of atoms (ie nuclei & electrons) are charged; the interactions of these charges leads to electrostatic forces in accordance with Coulomb's Law. (ie like charges repel, opposites attract)

WAit this is moving about, not electrical energy in the home

Anyways, where is coulombs law derived from?

 

[porcupinetree]

WAit this is moving about, not electrical energy in the home

Anyways, where is coulombs law derived from?

Coulomb's Law can be considered to be derived from Gauss' Law (which is essentially a law about electric flux), but in essence (at least at HSC level), Coulomb's Law is a fundamental law that exists because it successfully describes our experimental observations, rather than because it is derived from other laws/equations.

 

[InteGrand]

WAit this is moving about, not electrical energy in the home

Anyways, where is coulombs law derived from?

You can see the derivation of Coulomb's Law from the integral form of Gauss's Law here: http://physics.stackexchange.com/qu...equations-enough-to-derive-the-law-of-coulomb .

 

[Nailgun]

Why

btw just want to point out, that I know someone told you that you should ask 'why' to help improve your understanding (which I wholly agree with) but I don't think they literally meant just ask 'why'? lol

half of what your learn by asking questions comes from the question in and of itself - to really test your understanding you need to ask the right questions as well - like just randomly asking why isn't necessarily a bad thing, but if something confuses you or you don't understand it'll be much better for you to identify what exactly about it you don't understand. just asking "why?" is kind of like a band-aid, you'll get an explanation but it probably won't address the root of your confusion, and hence its much better for you to ask properly thought out questions pinpointing what specifically you don't understand, and when that inconsistency is explained you'll find it will be much much clearer and beneficial than just asking "why?" and getting a general explanation.

 

[cookie_dough]

btw just want to point out, that I know someone told you that you should ask 'why' to help improve your understanding (which I wholly agree with) but I don't think they literally meant just ask 'why'? lol

half of what your learn by asking questions comes from the question in and of itself - to really test your understanding you need to ask the right questions as well - like just randomly asking why isn't necessarily a bad thing, but if something confuses you or you don't understand it'll be much better for you to identify what exactly about it you don't understand. just asking "why?" is kind of like a band-aid, you'll get an explanation but it probably won't address the root of your confusion, and hence its much better for you to ask properly thought out questions pinpointing what specifically you don't understand, and when that inconsistency is explained you'll find it will be much much clearer and beneficial than just asking "why?" and getting a general explanation.

why? nah jokies i agree (even though i always just say why to my teachers in class)

 

[DatAtarLyfe]

That was the most sophisticated roast i've ever seen

 

[eyeseeyou]

btw just want to point out, that I know someone told you that you should ask 'why' to help improve your understanding (which I wholly agree with) but I don't think they literally meant just ask 'why'? lol

half of what your learn by asking questions comes from the question in and of itself - to really test your understanding you need to ask the right questions as well - like just randomly asking why isn't necessarily a bad thing, but if something confuses you or you don't understand it'll be much better for you to identify what exactly about it you don't understand. just asking "why?" is kind of like a band-aid, you'll get an explanation but it probably won't address the root of your confusion, and hence its much better for you to ask properly thought out questions pinpointing what specifically you don't understand, and when that inconsistency is explained you'll find it will be much much clearer and beneficial than just asking "why?" and getting a general explanation.

Please read the links below:

https://www.matrix.edu.au/how-i-topped-physics-at-fort-street-high-wasim-awal/
http://www.keystoneeducation.com.au...-can-do-to-ace-the-hsc-with-almost-zero-study

 

[InteGrand]

Please read the links below:

https://www.matrix.edu.au/how-i-topped-physics-at-fort-street-high-wasim-awal/
http://www.keystoneeducation.com.au...-can-do-to-ace-the-hsc-with-almost-zero-study

Why? p)

 

[eyeseeyou]

Why? p)

As for proof for why I ask "why"

 

[Nailgun]

Please read the links below:

https://www.matrix.edu.au/how-i-topped-physics-at-fort-street-high-wasim-awal/
http://www.keystoneeducation.com.au...-can-do-to-ace-the-hsc-with-almost-zero-study

did you read my post lol
im not saying don't ask why, or that it won't help - im saying you will gain a much better understanding if you ask why specifically to something you don't understand, and more importantly why you don't understand it

everything that you learn will either make sense or not make sense. if it doesn't

im like 90% sure that neither of those dudes meant just literally saying why over and over again after someone says somethings
what they were trying to say is that understanding will almost always trump rote-learning random bits of information - they are telling you to understand the "why", and this will happen much more effectively if you ask specific questions
like they're legit saying basically what im trying to say lol

tbh i feel like somehow you are trying to rote-learn the 'why' part as well lol, which is an impressive feat in and of itself
the point is not ask why and then gain knowledge that nobody else has because you can repeat a random why of something
the point is you understand why

"When you know why, you truly understand it, and it isn't just an isolated fact. Your brain can draw links between that fact and knowledge you know already, helping you embed it into your long term memory." - You have to be able to draw links like he says to all the content you know so it makes sense, and to do that you have to rid your self of any confusion or inconsistencies in your understanding by asking specific questions lel

"I found learning things not addressed by the syllabus but still relevant makes the subject intuitive so that you no longer need to spend hours at your desk memorising concepts you don’t fully understand."

It's not about "knowing more" than everyone else. It's about understanding it so it becomes intuitive. Like you legit don't really need to study that much after you understand the topic enough that it becomes intuitive. Just randomly asking why doesn't really improve that understanding, but asking specific questions tailored to what does not seem intuitive will help you immensely


annnyways do what you want lel