lucas
  • Member for 5 years, 10 months
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Does zero net force imply zero net torque?
10 votes

does it also leads to ... No, it doesn't. A simple Counterexample: Consider the figure below (the bar $\textrm {AB}$ and forces $F$ are on a plane parallel to $\textrm {xy}$ plane) We have $\Sigma ...

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Can there be an acceleration when no net force acts on a massless object?
8 votes

In a theory view point, it is possible. For example, consider figure below. The string is massless and inelastic (rigid). (There is no friction) The string moves with the mass $m$, so its ...

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Meaning of the value of the centripetal acceleration
5 votes

what does this value mean? This value means for maintaining of moon on the circular path, we need a force by amount of $\textrm{mass of the moon}\times\textrm{that value}$ How can this value be ...

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Newton's Second Law Confusion
4 votes

If a body is moving, this doesn't mean that a net force certainly must be exerted on it. It can move without any net force (First Law of Newton). You might say "How that body has started its motion ...

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Why do Newton's laws hold in a normal and tangential coordinate system?
Accepted answer
4 votes

I think confusion of the OP is related to the concept of the frame of reference. Frame of reference is a position in the space not a coordinate system. In other word, frame of reference is the ...

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What is the cause of rolling friction? & why is it less than sliding friction?
4 votes

First off, I think it is better that we draw free body diagrams and write motion’s equations related to a motorcycle (for example). Consider that motorcycle is moving with acceleration $a$ on a rigid ...

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Second Law of Dynamics and Pulleys
Accepted answer
3 votes

I think it is easier to consider to the string length. String length is constant, so we have: $$x_C+2x_A-x_B=\textrm{constant}$$ $$\Longrightarrow\;a_A=\large{\frac{a_B-a_C}2}\;\tag 1$$ On the other ...

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Otto and Carnot efficiency comparison
Accepted answer
3 votes

Otto cycle consists of two isochoric and two isentropic processes. If $T_4$ approaches to $T_1$, then $T_3$ will approach to $T_2$, because for Otto cycle, line $3\to 4$ in $T-s$ diagram must always ...

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When a person bends forward, does normal reation force change as a component of his weight is applied in torque?
Accepted answer
3 votes

Consider to configurations below: Necessary condition of equilibrium is $x_N=x_G$ When you bend and still are in equilibrium (configuration 1 and 2), then certainly $x_N=x_G$. When you bend, your ...

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Carnot engine basics?
3 votes

' if we employ any other process that is not adiabatic, say an isochoric process, to take the system from one temperature to another, we shall need a series of reservoirs in the temperature range $T_1$...

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What are the accelerations of blocks?
3 votes

$$l=x_A+(x_A-k_1)+k_2+k_3+2\pi R$$ $$k_3=x_B-2R-(x_A-k_1)$$ $$l=x_A+x_B+constant$$ so, we have: $$0=v_A+v_B$$ and$$a_A=-a_B$$

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Work energy theorem explanation
2 votes

Considering to your question and comments below it, I think that you have been confused about some assumptions. For example, when we assume that there is no friction, you should be able to imagine a ...

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Why does a critical point exist?
2 votes

Why does a critical point even exist? I think this question is equal to this one: "Why the width of the two phase region is bigger at lower temperatures and pressures?" Specific volume of liquids ...

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question on friction, 3 blocks placed one upon another
Accepted answer
2 votes

First off, you should draw free body diagram for each block. Then, you should recognize if relative motion between blocks occurs or they move simultaneously. For this purpose, you can consider to the ...

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Specific heat capacity for Adiabatic process
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2 votes

Specific heat capacity is defined for a substance not for a process. Specific heat capacity depends on the structure of the substance but, it ($C_P$ for example) can be measured by the formula $$C_P=\...

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Projectile question doubt
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2 votes

What should be the minimum value of $v_0$ in order to hit the monkey while it's in air? Minimum value for $v_0$ is when arrow hits to the monkey just before it (monkey) reaches to the ground. Or, ...

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Stable Sides of Polygon Objects
2 votes

About second part of your question, I should say that I couldn't understand it because it may the polygon like a star has no side contacted with the ground. About first part of your question, I ...

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Enthalpy of condensation
2 votes

Where am I going wrong? There is no liquid or solid that behaves like an ideal gas. So, there is no phase changing for any ideal gas. Ideal gas isn't a specific gas like oxygen, hydrogen, etc. It is ...

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Dissipative forces and reversible processes
2 votes

Because, dissipative forces convert some of the work to heat. If we want to have a reversible process we must be able to return system and its environment back to their initial states without any ...

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Is reversible work a point function?
2 votes

Reversible work is done by conservative forces and so doesn't depend on the path. Non-conservative forces like friction, generate irreversibility and in presence of those forces, we cannot have a ...

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Will a glass of water left in the fridge evaporate?
2 votes

Evaporation depends on vapor pressure of environment. If vapor pressure inside the fridge is lower than saturated pressure of water at $4^\circ C$, then the water will vaporize.

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What is meant by a "change in volume of a system"?
2 votes

What is meant by a “change in volume of a system”? "Change in volume of a system" means "change in volume of a system", not anything else. System is a hypothetical concept. There is no specified ...

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Relation between gravitational field and gravitational potential
2 votes

Gravitational field is a vector field and is determined by negative gradient of the gravitational potential. $$\vec g=-\vec\nabla \phi$$ Frome equation above, it is obvious that $|\vec g|=|-\vec\...

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Interpreting force components in statics problems involving inclined planes or similar
2 votes

Free body diagram of C is as below: Am I missing something important in interpreting the free body diagrams? Yes. You have assumed that $\vec N+\vec F+\large{\frac 12 m_C\vec g}=\vec 0$. But, this ...

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Young's modulus and geometry of test material
Accepted answer
2 votes

Young's modulus of a material doesn't depend on geometry. It is a mechanical property of material and depend on its structure. But, we cannot determine Young's modulus of a material by its structural ...

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tension and friction
2 votes

You can use these free body diagrams:

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Is "entropy" not a state variable for irreversible process?
1 votes

Entropy is a property of the system and it does not depend on the process that system experiences. Also, it does not depend on how you measure it. For irreversible process $\oint {\frac{{dQ}}{T}}$ is ...

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Why is force often a function of position and not the other way around?
1 votes

If I am pushing a block with variable force, we come up with an equation where force is a function of distance. But in reality, that makes no sense because it is my force that is causing a change in ...

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A problem on Heat and Evaporation (Solved)
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1 votes

First, you should calculate the amount of energy required for rising the temperature of the water from $38$ up to $100$ Celsius Degrees. If this is less than $2\times 10^5J$, then the difference in ...

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Conceptually, why is acceleration due to gravity always negative?
1 votes

I think the OP is confusing acceleration and direction of motion. Acceleration does not depend on the direction of the motion. According to the Second law of motion, (for constant mass) $\vec F=m\vec ...

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