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16 votes

In equation (3) from lecture 7 in Leonard Susskind’s ‘Classical Mechanics’, should the derivatives be partial?

The notation is a little sloppy from a purely mathematical point of view (although common in physics) so it might be causing a little confusion. To help clarify, it might help to use different letters ...
Andrew's user avatar
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10 votes
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Can a big mass defect make the mass negative?

If you apply no rules to the possible interactions then what you describe is possible. But the negative bound state mass can be avoided if we assume two things: A force field that has always positive ...
Jos Bergervoet's user avatar
9 votes

Why potential energy is not considered in the internal energy of diatomic molecules?

Note that potential energy is defined on a relative scale, and so we are free to chose the state which we call the zero potential energy state. Since the diatomic molecules are considered rigid, their ...
CompassBearer's user avatar
7 votes

When is minimum potential energy in simple harmonic motion not zero?

Potential energy can always be shifted by an arbitrary constant. For a Hooke's Law spring, this means we can write $U=\frac12 k(x-x_0)^2+U_0$. For a physical example, consider a mass on a vertical ...
rob's user avatar
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7 votes

When is minimum potential energy in simple harmonic motion not zero?

Energy has no absolute reference zero. The potential energy at zero displacement could be $0\,\rm J$, $1\,\rm J$, $10^9\,\rm J$, or $-10^9\,\rm J$ depending on where you set your (arbitrary) reference ...
Chemomechanics's user avatar
6 votes

Why potential energy is not considered in the internal energy of diatomic molecules?

You're right - there is an additional degree of freedom from the potential energy of the bond! In fact, there is also another kinetic degree of freedom from the relative motion of atoms as they ...
Carmeister's user avatar
6 votes

Can a big mass defect make the mass negative?

TL;DR: No, quantum field theory does not allow this. The general situation you describe is not at all exotic, and in fact this is why we have (meta)stable bound states. What you have termed 'mass-...
SethK's user avatar
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3 votes

How Can there be a Gravitational Potential when there is NO Gravitational Field?

You would be right, if you took your reference, at the center of the sphere, to be at a potential of 0. Throughout the sphere, you have a constant potential, which would remain 0. Generally, we take $...
ekl1pse's user avatar
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3 votes
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If I have a simple pendulum performing oscillations, whose string is snapped when it is at an extreme position, what will happen?

At the extreme position (max height), the mass on the end is momentarily at rest. If the string breaks at that moment, you just have a mass in the air acted on only by gravity. It will drop straight ...
Brick's user avatar
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3 votes

In equation (3) from lecture 7 in Leonard Susskind’s ‘Classical Mechanics’, should the derivatives be partial?

They are partial derivatives. From the chain rule, we have $$ \frac{\partial V(aq_1-bq_2)}{\partial q_1}= a V'(aq_1-bq_2),\\ \frac{\partial V(aq_1-bq_2)}{\partial q_2}= -b V'(aq_1-bq_2). $$ For ...
mike stone's user avatar
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2 votes

In equation (3) from lecture 7 in Leonard Susskind’s ‘Classical Mechanics’, should the derivatives be partial?

No. The notation means that the V on the RHS is a function only of one variable, and so its derivative is the simplest, one-variable derivative.
naturallyInconsistent's user avatar
2 votes
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Why does the mass-energy equivalence apply to binding energy when it is derived purely through kinematic means?

I understand that by defining the four velocity, multiplying it by the rest mass and taking the entire thing's norm we get E2=m2+p2 This is not always an accurate description of the process. For some ...
Dale's user avatar
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2 votes

When an object is thrown towards the sky it starts to gain potential energy, why?

The object has energy, whether it is kinetic or potential. There is a point in its trajectory where the object is not moving, and this is at the highest point of its trajectory. At this point, it has ...
ABetheGammow's user avatar
2 votes
Accepted

Question regarding gravitational force as external force

My doubt is if gravitational force is considered as an external force Yes, it is considered as an external force, an external conservative force. ...so how come can we apply Total mechanical energy ...
hft's user avatar
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1 vote

Strain energy stored in a bungee cord pulled at its midpoint

When a spring is halved, its spring constant $k$ is doubled. Because I'm treating this as a two spring system I need to double the value of $k$ that I'm using. Using a value of $k=280$ N/m gives $x=....
Imperator's user avatar
1 vote

When an object is thrown towards the sky it starts to gain potential energy, why?

There are two ways to view the exchange of kinetic energy and potential energy. But before I do, I'd like to point out that your learning of physics will be much much easier if you drop the concept ...
Cort Ammon's user avatar
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1 vote

Can a big mass defect make the mass negative?

This question leads to deep insights into what constitutes a particle relative to the vacuum. If you were to have a system of particles with binding energy less than the vacuum, the universe would ...
Xerxes's user avatar
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1 vote

Comparing Electric Potential Energy of two Charges

In the case that A and B both have the same positive charge: remember that potential energy associated with a position (it is not defined as something that requires two positions e.g. A and A') is the ...
Marius Ladegård Meyer's user avatar
1 vote

Why is work done by force $+mgh$ in the situation of throwing something up?

You are right, the work applied is not necessarily equal to $mgh$. To see this, let's look at energy conservation: $$K_0+U_0+W_{\text{n.c.}}=K_f+U_f$$ where $K_0$ and $K_f$ are the initial and final ...
BioPhysicist's user avatar
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1 vote

Why potential energy is not considered in the internal energy of diatomic molecules?

There is intramolecular potential energy and intermolecular potential energy. The first applies to the chemical and nuclear bonds of the molecule/atom. The second applies to the potential energy ...
Bob D's user avatar
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1 vote

In which situation the potential energy of a system is equal to its Gibbs free energy?

I can imagine situations that PES is equal to G, when we have two identities: PES = U (ideal conditions) U = G (Equilibrium or "no action" = zero Lagrangian) The potential energy surface (...
Alfredo Maranca's user avatar

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