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1 vote

Modelling friction as a conservative force

For systems with a Hamiltonian formulation, the Poincaré recurrence theorem (PRT) would indicate that most trajectories will eventually evolve back to a state arbitrarily close to their initial ...
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Modelling friction as a conservative force

It's not possible to do what you are attempting. For friction to be a conservative force, then the net work done by moving along a path where the start and endpoints are the same is zero which would ...
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4 votes

Modelling friction as a conservative force

Adding friction to a Lagrangian is not commonly taught. It is non-trivial, but not too difficult in the end. The key element is producing a "dissipation function" $D$ that we can use to ...
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2 votes

Can we have motion in systems where inertia is neglected?

I'm not completely sure I fully understand your question, but I'll try to give you an answer... It might help to think of this problem in a pseudo-relativistic context, wherein the physical motion of ...
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1 vote

Can we have motion in systems where inertia is neglected?

We sometimes assume a body has negligible mass, such as a rope in a pulley system where the pulley and weights on the ends of the rope have much greater mass than the light rope. This simplifies the ...
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1 vote

Can we have motion in systems where inertia is neglected?

It is not clear what is meant by inertia is neglected: Small/huge inertia It could be that the inertia is so small, that particle experience huge acceleration. We do often use this kind of an ...
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1 vote

Can friction or normal force be undetermined?

In general, there is no reason why all the reaction forces can be determined in a problem. Your intuition is biased by all the exercises you were assigned in an academic setting, which were hand-...
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0 votes

Energy dissipated by friction and entropy

It would be correct to assume that the entropy increase of the universe after the block has stopped is: $$\Delta S = \frac{K}{T}$$ In response to my query, you indicated that the "ambient ...
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5 votes

Can the value of friction force ever exceed value of applied force?

First, there is an important qualification to "the value of friction force can never be greater than the applied force". This refers to static friction. Indeed, you pose a scenario where &...
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2 votes

Can the value of friction force ever exceed value of applied force?

To answer the question in the title, the friction force can be larger than the normal force that is producing it. There is no restriction. Coefficients of friction larger than 1 are not common in ...
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19 votes

Can the value of friction force ever exceed value of applied force?

No. You've discovered the Class 2 Lever, which places the load between the input force and the fulcrum. You have correctly calculated that the friction force is 4 times the input force. The reason for ...
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0 votes
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How to know the direction of static friction with angular momentum?

In this case, the static friction is responsible for generating the circulation in the case of rolling without slipping. The reverse occurs when friction is a resistance to rolling. This is similar to ...
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0 votes

Energy dissipated by friction and entropy

It would be correct to assume that the entropy increase of the universe after the block has stopped is: $$\Delta S = \frac{K}{T}$$ This would be correct only provided the temperature of the "...
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1 vote
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Will the inner gimbal continue to rotate if no friction?

In order for the gyroscopic effect to be elicited motion is required. When the rotation rate of the outer gimbal goes back to zero the gyroscopic response to it ceases. Later edit: In writing the ...
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1 vote

Energy dissipated by friction and entropy

If the initial temperature and the final temperature of the block are both T, then applying the complete version of the first law of thermodynamics to the block gives $Q=-K$, where Q is the amount of ...
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2 votes

Checking whether my conclusion are correct or not regarding turning of car/bike on flat road

No, first statement is not true. The number of friction forces which are acting here are 2, i.e one along the circular path which is making the car move even if it's not being accelerated (although ...
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Work done by static friction on a car

The answer by @stafusa is correct. The increase in kinetic energy (KE) of the car is due to the decrease in internal energy of the car (from combustion, batteries, etc.) This can be understood using ...
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1 vote

Traction Torque Effect On A Rotating Wheel

Here is a much simplified schematic diagram of the rear end of the transmission chain as a car is accelerating towards you. For the transmission shaft the net torque on it, $\tau_{\rm TE}-\tau_{\rm ...
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1 vote

Traction Torque Effect On A Rotating Wheel

For any mechanical system, every piece of it will obey Newton's laws. For a system like the one you've shown, each colored part will obey Newton's laws during operation (this analysis is usually done ...
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2 votes
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Traction Torque Effect On A Rotating Wheel

engineers usually say that the wheels driving torque is always equal to the traction force times the radius of the wheel. That's a simplification where the mass of the wheel is insignificant compared ...
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1 vote

Traction Torque Effect On A Rotating Wheel

If the torque due to traction equals that of the motor the angular acceleration is indeed zero. Obviously when a vehicle accelerates the driving force of the motor overcomes that of the friction. It ...
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Traction Torque Effect On A Rotating Wheel

This wheel would never accelerate as two opposing torques of equal magnitude are acting on the wheels such they should cancel each other creating ZERO acceleration. No. You need to learn what free ...
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2 votes
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How can chalk write on a blackboard?

If you looked at the blackboard with a magnifying glass, you would see that it is bumpy. When you drag the chalk across it, the bumps catch on the chalk particles. There are forces parallel to the ...
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0 votes

What is the role of intermolecular bonds in friction?

The coefficient of friction is a unitless ratio of the force opposing the direction of motion (friction) to the normal force. Any phenomena that changes the frictional force will change the ...
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What is the role of intermolecular bonds in friction?

Friction results from the transition of an ordered macroscopic movement into unordered microscopic movement. This transition is caused by the high dimensionality of the corresponding (quantum)dynamic ...
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1 vote

Can you avoid the cubic velocity-to-drag relationship by covering the entire surface with wheels?

You seem to vastly underestimate the amount of wheel friction involved. Anything involving grease etc. in order to reduce bearing wear will certainly have more viscous friction than air blowing past a ...
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  • 6,863
2 votes

Can you avoid the cubic velocity-to-drag relationship by covering the entire surface with wheels?

Without wheels, you have air blowing past the plane at the speed the plane travels. If you add wheels, air blows past the plane at speed $0$, because the outer surface of the wheels move backward to ...
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2 votes

Can you avoid the cubic velocity-to-drag relationship by covering the entire surface with wheels?

No. For something like airplane, drag mostly isn't caused by air "rubbing against" the object, it is due to air molecules "bouncing off" the object. The wheels don't reduce the ...
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1 vote

Coefficient of friction between magnets

It's zero, both definitionally (friction is a force between materials in contact, and they aren'tin contact) and practically, with friction being used as a catch all for dissipative forces. Neither ...
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0 votes

Friction on a moving car

What causes a car to travel at constant velocity? A car travels at constant velocity when the torque applied to the drive wheel(s) produces a forward static friction force between the tire(s) and ...
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Friction on a moving car

Ideally, there is no friction interacting with the car at constant speed. When an object slides over a surface, kinetic friction appears. But it is constant (at not-too-high speeds) and doesn't ...
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1 vote

If a collar of aluminium is on a slightly tapered shaft will heating the pulley near the centre cause the i/dia to expand and release the collar?

The coefficient of thermal expansion for aluminum is greater than the coefficient of thermal expansion for steel, so heating the shaft should work. For more info, see this and this.
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Finding the Smallest Possible mass of an object

Vertical forces: Gravity down ($F_g = mg$), Hosni's applied force down, ($F_y = 16.13N$), a normal force up ($F_N = F_g+F_y$) Horizontal forces: Hosni's applied force forward ($F_x = 42.02N$), ...
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Finding the Smallest Possible mass of an object

Hint: The static friction force is a variable force that will equal and oppose the horizontal component of the applied force up until the maximum static friction force of $f_{max}=\mu_{s}N$ when ...
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1 vote

End motion of an empty spherical shell with a ball rolling on it's inner surface

Sounds like initially an external observer would see the shell not spinning, but oscillating around as the ball rolls inside. Friction will couple the motion of the ball to the rotation of the ball. ...
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If we put a number of identical boxes on top of each other and apply a linearly increasing force to the bottom, will they start slipping one by one?

SEE EDIT BELOW. On the assumption you mean a constant horizontal force applied to the vertical pile of boxes... The force applied to box 0 (bottom) is transmitted to box 1 by friction. Taking the ...
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