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Physics 101- About Force

I know that force is $F=−∇U$, but isn't it for the forces that's been done by the system itself? Like when i pull up a ball with external force pointing upwards, shouldn't a ball's potential energy ...
0 votes
0 answers
36 views

Angular acceleration :( [closed]

If i calculate the angular acceleration of a rigid body in rotational motion choosing 2 different points does it give the same answer?
0 votes
1 answer
32 views

If friction and normal force are both the components of contact force, shouldn't the friction be repulsive?

Is friction due to intermolecular attractive forces or repulsive ones. Since both friction and normal force are the components of contact forces, shouldn't friction be repulsive.
0 votes
0 answers
14 views

Why do you feel the difference in the force required when a muscle contracts and relaxes even if you apply the same force to an object?

Think about a person lifting or lowering a 50kg object vertically. Lift and lower at constant speed. At this time, the force exchanged between the person and the object is 490 N, and the person is ...
0 votes
0 answers
21 views

Painter on scalffold - Kleppner and Kolenkow Problem 2.12 [closed]

I am currently trying to teach myself mechanics by reading Kleppner and Kolenkow's Introduction to Mechanics, and I've hit a bit of a snag on Problem 2.12. A painter of mass M stands on a scaffold of ...
7 votes
6 answers
3k views

Can there be acceleration without work?

Since $W=Fs$, $F=\frac{W}{s}$. When you substitute this in the formula for acceleration, $a=\frac{F}{m}$, you will get that $a=\frac{W}{ms}$. Then, when work equals zero, acceleration will be zero.
0 votes
3 answers
70 views

Conservation of momentum vs newton's second law

I saw this question from a book: An empty sled is sliding on frictionless ice when Susan drops vertically from a tree down onto the sled. When she lands, does the sled speed up, slow down, or keep the ...
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1 vote
2 answers
88 views

Is Energy stored Force?

I am currently studying the relationships between energy work and force. I am trying to conceptualize them into one concept of causality. When a force is applied work is done, and energy is ...
3 votes
2 answers
142 views

Follow up question on a block on an accelerating inclined plane

A follow-up on this post: How can an accelerating inclined plane prevent a block on it from sliding? Farcher's answer states that "If F is larger than in the no relative movement condition then ...
1 vote
0 answers
39 views

Hard problem of pulleys [closed]

A string passes over a frictionless, massless pulley attached to the ceiling A mass $m_1$ hangs from one end of this string, and a second massless, frictionless pulley hangs from the other end. A ...
0 votes
2 answers
85 views

Why do cars move slightly backwards just before coming to rest?

You've probably noticed this before: you're in a car or other wheeled vehicle, the brakes are applied, the car's velocity reaches zero, and then the car actually moves backward a tiny amount before it ...
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1 vote
0 answers
22 views

Classical mechanics problem of elevators [closed]

A passenger elevator consists of an elevator cage of 900 kg (empty) and a counterweight of 990 kg connected by a cable running over a pair of pulleys (Figure 6.9). Neglect the masses of the cable and ...
1 vote
0 answers
28 views

Proof of principle of transmissibility of force

The principle of transmissibility states The point of application of a force to a rigid body can be moved anywhere along its line of action without changing the external reaction forces. My question ...
0 votes
1 answer
49 views

Is Newton's laws formulated using laboratory time?

The second Newton's law can be written as (in SI units) $$ \frac{d}{dt}\vec p = \vec F. $$ Newton was considered Galilean transformations and the existence of a "absolute" time. Now suppose ...
1 vote
1 answer
25 views

Average Tension in the string of a pendulum: Determining radial component of weight

Self-studying Classical Mechanics right now and was working through an example until I got to a point where I felt certain questions need be addressed. I will list the problem statement, the example ...
1 vote
2 answers
23 views

Average Tension in pendulum string: Understanding the radial $F = ma$ equation

Self-studying Classical Mechanics right now and was working through an example until I got to a point where I felt certain questions need be addressed. I will list the problem statement, the example ...
1 vote
1 answer
28 views

Resolution of force vectors

So, I have had this query for like the longest time, ever since I first studied this topic. So, take a force vector $F$ that is making an angle of say, 30 degrees with the horizontal axis. Now, I want ...
1 vote
1 answer
31 views

Use of Instantaneous axis of rotation (IAOR) in a question of mechanics give different and wrong answer

The above situation can be solved easily when we go in frame of point C then point C will come at rest and mass "m" will do circular motion about point C with 3v velocity and then using ...
1 vote
3 answers
61 views

Law of inertia in rotation

Consider an object rotating about its own axis. If the law of inertia is applicable, the object should keep rotating with the same angular velocity if no external torque is provided, but how is the ...
1 vote
0 answers
29 views

Can a bicycle whose front wheel cannot turn left/right stay upright?

Most sensible explanations of why a bicycle stays upright involve the turning left/right of the front wheel. If a bicycle's front wheel cannot turn left/right, can it stay upright while being pedalled?...
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0 votes
1 answer
45 views

Is a velocity-dependent force $\vec{F}$ that doesn't do any work on an object a conservative force? [duplicate]

Let's consider a point like object with mass $m$ upon which acts a force $\vec{F} = \vec{c} \times \vec{v}$ ($\vec{c}$ is supposed to be a constant vector). Given that $\vec{F}$ is perpendicular to $\...
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1 vote
2 answers
54 views

The net force received by the bus handle during the acceleration of the bus

Re-post the question by complementing the inaccurate information. First, I'm just an ordinary person who's interested in physical phenomena and physics. I apologize for not expressing it through ...
5 votes
5 answers
184 views

Why don't weighing machines show the weight of the atmosphere?

The school experiment of hanging two balloons, one filled with air, other empty, on a ruler, show that air has weight. A person has weight. It's shown on a weighing machine. A pencil has weight. It's ...
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0 votes
1 answer
58 views

Field due to objects if inverse square law does not hold [closed]

There is a hypothetical question about what will happen to the field of objects if inverse square law is replaced with something else. For example, it can be proved that if force is proportional to ...
1 vote
0 answers
49 views

Force required on a projectile to maintain its initial velocity [closed]

As per the Newton's Second Law; $$\mathbf F = ma$$ and, $$ \mathbf a = \frac{v-u}{t}$$ and, the initial velocity of a projectile propelled with an angle $\theta$ should be, $$\mathbf v_i = \sqrt\frac{...
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2 votes
1 answer
53 views

Mechanics of book falling on it's side [closed]

I have the following question that I'm struggling with. Imagine you have a very thin book (we consider it's thickness to be 0) that sits upright. At some point the book falls to it's side. How can we ...
0 votes
1 answer
49 views

Paradoxical behaviour of wedge on an accelerating incline

This is a standard physics problem commonly seen in many textbooks. For the top wedge to not slip on the bottom wedge, the acceleration has to be $$g\frac{\sin\theta-\mu\cos\theta}{\cos\theta+\mu\sin\...
0 votes
2 answers
117 views

Why do we write force = mass × acceleration? [duplicate]

Force is directly proportional to mass and rate of change in velocity i.e., acceleration. So why do we write force as mass times acceleration? I mean why do we multiply mass by acceleration?
1 vote
3 answers
95 views

Why $F = m(v_f - v_0)/2$? [closed]

Force is directly proportional to mass and velocity and inversely proportional to time so why don't we write $F=1/t+m+v-v_0$ where $m$ is mass, $v$ is final velocity, and $v_0$ is initial velocity?
-1 votes
0 answers
15 views

Propulsion in Space (Vacuum) using only conductor in Magnetic field [duplicate]

While browsing for this cool topic , I've found the following interesting patents about SPace propulsion in Vacuum using Lorentz force for Conductor in Magnetic field : https://patents.google.com/...
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7 votes
4 answers
879 views

Does an open or a closed cage of canaries weigh less when they are in flight? [duplicate]

Okay this is a bit of an old classic, but I don't think I've heard a good reasonable explanation for what happens: If you put a cage of canaries on a weigh scale and they take off does the scale still ...
3 votes
2 answers
153 views

Why do levers work?

If we have 3m beam with a fulcrum 1m from one end, we will find a balance by having a 1kg weight on the long end of the beam and a 2kg weight on the short end. Similarly, I will need much less ...
0 votes
2 answers
41 views

Is it practical to texture the piston surface of a pneumatic cylinder to increase the pressure area? [closed]

Would it be practical to texture the surface of a piston in a pneumatic cylinder to increase the pressure area and therefore the thrust force? F = P * A For ...
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0 votes
1 answer
68 views

Free falling elevator - A person would "levitate"? [duplicate]

If an elevator goes into free fall, assuming there's no friction or anything like that, would it actually float? From what I understand, this would only happen if the elevator falls with an ...
0 votes
3 answers
42 views

What is the Direction of Frictional Force on a Person Pushing a Refrigerator to the Right?

Suppose on a 2D plane a person pushes a refrigerator to the right. The only reason they are able to do that is due to the presence of frictional force. Normally if we look at the shoes of the person, ...
4 votes
4 answers
177 views

Intuition behind $p = mv$ and $F = ma$

I am only familiar with physics at an elementary level; and while that is true, it would be nice if I could clear up some clashes with intuition I'm having before progressing further. What is the ...
0 votes
1 answer
25 views

Why is the Horizontal Tension same here?

Our sir told us that the horizontal tension will be equal throughout the string but why
1 vote
2 answers
75 views

Can I weight a weighing machine by putting it upside down?

For the sake of this question let us assume a flatbed scale where I can put the mass on top in order to measure on a flat surface which forms the top of the scale: Will it give correct reading if I ...
-1 votes
1 answer
32 views

What forces act on the block? [closed]

I can not understand why the forces N1 and N2 act on the block. What are these forces and why did they appear?
-1 votes
2 answers
68 views

Motivation for definition of work [closed]

Why do we take the dot product in the work energy theorem? Consider the integral $$\int\vert\vec F\vert\vert d\vec r\vert$$ Why don't we define this to be work done for example, instead of $\int\vec F\...
0 votes
1 answer
61 views

What is point of application of force? [closed]

My textbook said that point of application is the exact location at which a force is applied to a body. But I know that there are some forces that their points of application outside the body (like ...
0 votes
1 answer
70 views

Inconsistency regarding the spatial trajectory of a particle subject to a given force field [closed]

I have recently been trying to formalize a mathematical method (for my own recreational purposes) to work out the shape of the path that a particle traces out in space if we are given the resultant ...
0 votes
0 answers
21 views

Why do we consider the whole process, taking a single moment? Universality of the vector equation

I have considered a simple model for describing the elastic force vector of a spring. First, I chose a reference frame in an arbitrary way, then I drew the necessary vectors, we get a ratio that ...
0 votes
1 answer
39 views

Can We Have 0 Normal Between Any Two Bodies Just Touching Each Other

I am a bit confused... Here if we see x-axis forces they are getting detached from each other. So To Resist them The Normal Should Be Zero. I am not sure if I am applying the right logic or not but ...
0 votes
2 answers
56 views

How To Find Direction of Normal Contact Force?

I am a little bit confused. while doing questions I can see direction of normal forces are different. In Some Cases, It is perpendicular to the contact surface and towards the object on which normal ...
0 votes
1 answer
52 views

Illogical conclusion about a mass on a spring [closed]

If you place a weight on a spring and it is an equilibrium, then you have this equation: $mg = kx$ you would solve for k and get: $k = mg/x$ but, if we used conservation of energy, assuming that when ...
0 votes
2 answers
81 views

Why is a ball that is moving in one direction and spinning in the opposite slowed down if the force of friction is tangential?

If a ball has linear and angular velocity such that there is a slip between the surface of the ball and ground, why does linear velocity of the center of the ball decrease if the force of friction is ...
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2 votes
2 answers
124 views

$F=ma$. $p = mv$. What's $mx$?

So I know that $$F=ma$$ ($F$ is force, $m$ is mass, and $a$ is acceleration). I also know that $$p=m\int a dt=mv$$ (Where $p$ is momentum and $v$ is velocity). So I was wondering if the following ...
0 votes
3 answers
129 views

Derive the Law of Conservation of energy from Newton's 3rd Law of Motion

I'd like to derive a conservation principle for the mechanical energy, as sum of kinetic and potential energy, for a multi-body point mass isolated system using the $2^{nd}$ and $3^{rd}$ Newton's ...
-1 votes
1 answer
29 views

Optimising circular motion for high downforce vehicles

I'm doing a school assessment where i am trying to optimise the entry speed into a corner for an F1 car. With this there are a few assumptions for the sake of simplicity. entry speed = exit speed, as ...

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