5
votes
Why is friction required to rotate a non-ideal pulley-string system?
Friction between the rope and the pulley results in a torque, causing the pulley to start rotating from rest. Without friction, there is no torque, and no rotation - in this scenario, the rope simply ...
- 10.4k
4
votes
Accepted
Can the weight distribution of a partially supported rigid mass be determined?
I was too late to help in the chat when you were discussing this question.
For any $0<L_2\leqslant L_1$ so that things are interesting, simply first consider chopping the $L_2$ part off. This way, ...
- 11.1k
4
votes
Accepted
Why doesn't Newton's Third Law prevent work from being done?
You are absolutely right. You do work on the object, and the object does an equal amount of (negative) work on you. It cancels out and this system of you-and-object doesn't gain any energy and hence ...
- 52.3k
4
votes
Accepted
Is centrifugal force in this case thrust force?
The short answer is that there will be no net propulsion. Newton's third law dictates that action is equal to reaction. If the bucket was thrown and released off the front of the skateboard, the board ...
- 10.1k
4
votes
Will there be any frictional force from surface when an external force acts upon a body which is in contact with wall?
Let's assign a value of $0.5$ for the coefficient of static friction and $0.2$ for the coefficient of dynamic friction. This means the limiting static friction would be $2.5$ Newtons and the dynamic ...
- 10.1k
3
votes
Accepted
Will there be any frictional force from surface when an external force acts upon a body which is in contact with wall?
All of those scenarios are possible. The system is statically indeterminate.
To determine which of these cases is correct requires additional information. Specifically, we need to know the stress in ...
- 109k
3
votes
How do we consider kinetic or potential energy of earth while applying conservation of energy?
Since momentum is conserved, if the block has a change in momentum of
$$\Delta p = m\Delta v $$
then so does the Earth (with a minus sign).
That means the Earth takes up an energy of:
$$ \Delta E = \...
- 39.5k
2
votes
Is centrifugal force in this case thrust force?
@SolomonSlow I understand with case push and pull bucket, but don't really understand in my case, when will skate go forward and when backward?
In my comment (above) I asked you to imagine yourself ...
- 16.2k
2
votes
Particle sliding on a sphere
This is my slightly simplified solution. I would like to thank my good friend @Bml for assistance with the calculus involved. (He is a bit of a whizz.)
The gravitational force acting on the sliding ...
- 10.1k
2
votes
Why is friction required to rotate a non-ideal pulley-string system?
Without friction, the rope would simply slide over the roll with no rotating motion.
- 2,416
2
votes
Can the slack in 2 different strings (ideal) be transferred to one another?
There is one continuous length of string going round all four pulleys. Let's split this into five consecutive lengths $l_1 \dots l_5$ where:
$l_1$ is the distance between the ceiling and the centre ...
- 60.3k
2
votes
Trouble with the concept of external force on a system
There are many ways to show that there is another external force acting on the two mass and string system other than the two gravitational forces on the masses and the normal force on mass $m_1$, the ...
- 99.9k
1
vote
What is the maximum displacement at which a series of blocks can be displaced vertically?
I remember such a problem, the displacement of cubes placed one on another was only in one direction. The total displacement could be arbitrarily large, and maximum displacements formed the harmonic ...
- 27.5k
1
vote
Does an uniform rod hinged at the center rotate when released from any angle?
The rod will not exhibit rotational motion if it is released without any initial angular velocity about its center of mass.
In the context of a uniform gravitational field, and in the absence of any ...
- 11
1
vote
Is centrifugal force in this case thrust force?
First of all, I'm confused by you labelling going to the left as "forward". The centrifugal "force" will be to the right.
As to the meat of the question, centrifugal "force&...
- 9,116
1
vote
Can the slack in 2 different strings (ideal) be transferred to one another?
If you cut the string you obtain the string tension $~T~$
I) write the equations of motion
$$ m\,\ddot X=-m\,g+2\,T\\
m\,\ddot Y=-m\,g-2\,T+T\\
m\,\ddot Z=-m\,g+2\,T$$
II) obtain the tension ...
- 12.8k
1
vote
Trajectory of a bird flying over the earth
it would see a centrifugal force acting on the bird, the weight force
acting on the bird and a buoyance force that keeps the bird on the air
The buoyance force does not keep the bird in the air. If ...
- 10.1k
1
vote
Trajectory of a bird flying over the earth
The centrifugal force acting on the bird would point otwards the bird trajectory. The weight force would point inwards the center of the globe and the buoyance force would point the opposite direction ...
- 109k
1
vote
Animating the path of a moving object placed at the top of a circular surface and moving into free fall
The Animation
The blue ball is rolling without friction on the circular surface. It loses contact with the surface when the contact force between the ball and the surface becomes zero. At this point, ...
- 12.8k
1
vote
Work done by static friction on a car
This answer is correct, but I'd like to emphasize an important point:
Work and total energy depend on the reference frame.
In the frame where the road is at rest, the car is gaining kinetic energy, ...
- 3,833
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