Newtonian mechanics covers the discussion of the movement of classical bodies under the influence of forces by making use of Newton’s three laws. For more general discussion of energy, momentum conservation etc., use classical-mechanics, for Newton’s description of gravity, use newtonian-gravity.

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The role of mass in the tablecloth trick

Apologies if this has already been answered, but I have a question about the role of mass in the classic tablecloth trick, where the demonstrator pulls the tablecloth out from underneath a set of ...
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4answers
2k views

Why is normal force perpendicular?

I realize "normal" is just another word for perpendicular, but semantics aside, what causes normal force to be always perpendicular to the plane? For example, on an inclined plane, why is it that the ...
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92 views

Calculate the Earth’s velocity in its orbit (assumed to be circular) around the Sun [closed]

Data: GM of the Sun: $\text{GM} = 1.327 \times 10^{20} \;\mathrm{m^3 s^{-2}}$ Radius of the Earth’s orbit: $r_{Earth} = 1.496 \times 10^{11} \;\mathrm{m}$ Orbital period of a planet in seconds: $T = ...
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1answer
76 views

Whether a large or a small ball fall faster in the air?

Given a ball falling under gravity is subjected to air resistance, after performing a differential to the drag equation, I get: $$g-Z(v^2)/r = a = v',$$ (where $Z$ is a constant.) How can I know ...
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2answers
85 views

How do you choose direction of moment of inertia?

If a car is accelerating forward from rest with no air resistance while weight and normal forces act on the wheels, in which direction is the moment of inertia? Is it positive, clockwise or anti ...
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1answer
45 views

What's the average speed (along $z$) and the average position (along $z$) of an object in free fall?

I'm looking to calculate the average speed (along z) and the average position (along z) of an object in free fall. The initial instant is $t_0$ and we have: $z(t=t_0)=z_0$ $v_z(t=t_0)=v_0=0$ I ...
2
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1answer
141 views

Why does the rule that elastic collisions are at 90 degrees in 2 dimensions not apply?

When one object collides with another object of the same mass in a 2D plane, we know that we can derive that the angles that the objects leave the collision at add up to 90 degrees in a perfectly ...
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2answers
82 views

Why is kinetic energy calculated using speed?

Why is kinetic energy calculated using speed? Since speed is distanced covered, and if a car moves 100 meters around a circular track -- stoping after moving half of the distance of the track -- the ...
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1answer
91 views

Spring rotated in uniform circular motion

Why does a spring stretch when rotated in uniform circular motion? The horizontal rod containing the massless spring(stiffness = k) and block of mass 'm' is rotated uniformly about point P. ...
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5answers
1k views

Zero gravity means zero friction?

The frictional force acting on a body placed on a horizontal plane is $F=\mu{R}$ where $R$ is the normal reaction and is equal to weight of a body in this case. And $\mu$ is the coefficient of ...
1
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1answer
172 views

Center of mass (COM) of a uniform quarter disk [closed]

I was trying to calculate the coordinates of the COM for a uniform quarter disk. By symmetry, it must lie on the angular bisector of the central angle. Also, $A=\frac{\pi R^2}{4}$, thus ...
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3answers
46 views

Multi-Force Lift

Background: I am creating a 3D game. A ship has 3 thrusters that apply force up (Z+) to counteract the force of gravity (Z-). I am trying to figure out how much thrust to apply to each thruster to ...
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1answer
61 views

Contradiction of total energy of a system? [duplicate]

I consider a situation in a system in which an observer is sitting in body of mass $M$ and another observer in a body of mass $2M$, both moving with velocity $v$ towards each other. If observers in ...
2
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1answer
45 views

Potential Energy in a System and its Relation to the Total Energy

In this answer it was stated that potential energy is a property of a system and not an individual particle. If we have two particles (1 and 2) interacting via a conservative force, we can write an ...
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0answers
74 views

How to measure the initial velocity of a potato gun?

I have made a 2m potato gun (It's like a cannon - the noise makes your ears buzz for some second :) ) Its uses alcohol as fuel. an igniter fires. then the potato will be shot out. anyway. as it's ...
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1answer
118 views

If a body slides down a frictionless inclined plane what will be the net normal force?

If a body(m) slides down a frictionless inclined plane (M), will the net normal force between the ground and the inclined plane be (M+m)g ? I feel it should be less than (M+m)g. This is because one ...
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2answers
163 views

Relation of spring constant with mean radius of spring

My teacher says that spring constant depends on its radius. I tried to understand it, and checked many questions in this site and other sites. All of them say that spring constant depends on number of ...
0
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1answer
57 views

Relation between accelerations of block and tangential acceleration of the pulley in pulley block system

I was doing some pulley block problems in rotational mechanics and almost everywhere when the pulley is rotating and some masses are connected by a light rope(for example I am taking a two block and 1 ...
0
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1answer
31 views

How to develop the static and kinetic friction formula? [duplicate]

How do you end up with the formula for Amontons' first law of friction? ($F_s = \mu_s \times N$) or ($F_k = \mu_k \times N$). I know how to use the formula. Now I need to know how to get to it.
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2answers
47 views

Static vs. kinetic friction and the “normal-force” considered

Consider two cases. First, we have a box that a person applies a force to (say to the right). The force of friction (static) is then directed to the left. Second, say that the box is moving at ...
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5answers
1k views

Where does the force appear when considering object interactions in another reference frame?

Imagine I am sitting on an asteroid with my buddy and drinking a beer. When the bottles are empty we throw them simultaneously in opposite directions perpendicular to the asteroid's movement. What ...
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2answers
43 views

Why does a block 2 on a oscillating block 1 start sliding at the maximum acceleration?

A block of mass $ m_{1} $ is oscillating horizontally with another block on it of mass $ m_{2} $. There's friction "k" between both blocks, so the thing is why the second mass starts sliding at the ...
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1answer
153 views

Is momentum truly conserved? [closed]

Suppose I have a system of a person holding a rock on a frictionless sheet of ice. He throws the rock at an angle above the horizontal to propel himself off the ice. Is the momentum of that system ...
2
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3answers
158 views

Terminal velocity and distance traveled with constant but limited power

I'm trying to model how far to move an object over time according to a power applied resisted by friction. So maybe... an object accelerates at a certain rate until the power provided can no longer ...
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1answer
33 views

How do I calculate the speeds in x, y, and theta of a spinning rod?

Suppose the object looks like the diagram below (it is the horizontal rod). On the vertices, are two velocity vectors $v_r$ and $v_l$. The question is: how is the motion of the rod affected by these ...
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2answers
42 views

What is a center of gravity?

I have tried to search the definition of it up on Google, but the explanations of center of gravity were very confusing and I had trouble understanding them. Can you explain to me what center of ...
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1answer
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0
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1answer
90 views

Physical meaning of eigenvectors of mass matrix

What is the physical meaning of the eigenvectors of the mass matrix? If I consider a 2-dof system with one mass linked to two orthogonal springs and I write the equations in any orthogonal system of ...
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3answers
84 views

Path followed by centre of mass of a ball when ball breaks up in two parts due to internal stresses

A ball was moving along a parabola and it breaks up into two parts. How can I say that the centre of mass will follow the same parabola ? I know that ( for simplicity I am assuming that the ball is ...
2
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0answers
108 views

Lagrange: when a potential force, when a generalized force?

Consider the following case of a drum unrolling a mass that is on a massless string wrapped around the drum: According to my professor, here we must consider the mass $m$ being in a gravitational ...
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2answers
430 views

Half-atwood machine with accelerating pulley

This is a follow-up to my previous question, in which I am now trying to calculate the acceleration of the cart (as before, the block surfaces are frictionless). The mass $m_2$ is attached to $M$ via ...
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3answers
347 views

How is normal force distributed along the surface of contact?

Help me settle this argument. A mass $m$ is placed on a thin diving board. The base of the diving board has mass $M>>m$. Does the board tip over? I drew the following FBD and concluded there ...
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2answers
115 views

Physical intuition about the inertia tensor

I'm studying Mechanics on Goldstein's book (Classical Mechanics) and Spivak's book (Physics for Mathematicians) and I'm in doubt about the physical intuition about the inertia tensor. On both books, ...
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1answer
34 views

Speed of different inclined plane [closed]

Assume friction-less, an object was release from the top, what is its speed at the lower end of the slope? I tried $v= \sqrt {2*9.0m/s^2*5m}$, but I doubt if it's a correct answer, any help?
2
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1answer
44 views

Given an equation of an elliptical orbit, is it possible to find satellite´s speed at a certain point?

As the heading says: given an equation of an elliptical orbit, is it possible to find satellite´s speed at a certain point? I'm playing a bit with simulations of planets and satellites in the solar ...
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2answers
42 views

Why time of flight remains same for a projectile even though collision takes place?

Why time of flight remains same for a projectile even though collision takes place ? Suppose a ball is projected with some velocity V with some angle θ the the time of flight is T. Now if another ...
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0answers
51 views

Hollow Iron pipe electromagnet? [closed]

How strong would a electromagnet be if I use a hollow Iron pipe as the core? The thickness of the pipe will be 2-3 cm. How much weaker would this electromagnet be compared to a non-hollow ...
0
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1answer
82 views

Torque when net external force is zero

I was studying force couple and my teacher said that in this the torque about any point is same. That led me to wonder if in any case if net external force is zero then is torque about any point in ...
1
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1answer
85 views

Contradiction in a simple torque/rotation problem - two ways of calculating external force don't agree

Suppose we have a rigid system of two point objects (both of unit mass) connected with a massless rod, with the objects horizontal on the x axis, at a distance $r_1$ and $r_2$ from the origin, ...
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2answers
94 views

Kinetic energy and work confusion [closed]

I know that $\frac{1}{2}mv^2$ is derived from $W = \int \vec F \cdot\ d\vec s$, but are there exceptions to the kinetic energy formula? Newton says that unless an external force is applied, a body ...
1
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2answers
43 views

Exercise pulleys and accelerations [closed]

The system shown has ideal massless pulleys and no friction. The pulleys 1 and 2 are fixed and the pulley 3 is mobile. The mass m2 is rigidly attached to the center of the pulley 3 by a support ...
1
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1answer
36 views

Gravitational PE lost v Elastic PE gained in mass - spring

If a spring has a load $m$ added to it (and so is extended by $x$), the gravitational potential energy lost by the mass will be $mgx$. The elastic potential energy gained by the spring is ...
3
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4answers
275 views

Conservation of momentum in a baseball

Conservation of momentum: A thought experiment. A baseball is placed on top of a baseball holder, the kind used to train young batters. A batter hits the stationary ball perfectly horizontal, sending ...
4
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0answers
105 views

Alternate Formulation of Kinetic Energy for Lagrangian

So I have a question regarding this system: It is supposed to be a simple model of an aircraft with the fuselage idealized as a concentrated mass $M_0$ and the wings modeled as rigid bars carrying ...
2
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2answers
269 views

Pulley system on a frictionless cart

Let's say you have a pulley set up as below on a cart, with a massless pulley and string. The mass hanging off the side is attached via a rail, and all surfaces & pulley are frictionless except ...
4
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0answers
34 views

What is the specific source(s) of sliding kinetic friction

In simplistic (K-8) physics classes, it seems to be generally instructed that the friction between two moving surfaces is due to the unevenness of each surface and the microscopic roughness. However, ...
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1answer
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How can we apply Newtons laws, or kinematics to solve a problem like this one?

Problem: Two objects with masses 5.00 kg and 2.00 kg hang .600 m above the floor from the ends of a cord 6.00 m long passing over a frictionless pulley. Both objects start from rest. Find the maximum ...
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0answers
24 views

Initial conditions for a massive objects to follow a path

Suppose I have a path, such as the one traced out by $r^2 = \cos(2\theta)$, and $n$ objects with mass $m$ at equidistant points on this path. What velocities should each object initially have in order ...
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2answers
277 views

Tension in rope between falling objects

I got a mass m connected with a rope to a mass 2m which is centered directly underneat it. The masses are falling with a constant speed v. Would it be correct to say that the tension in the string is ...
2
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1answer
102 views

Physical interpretation of the canonical scalar product in linear dynamics

Consider a unforced, undamped, linear mechanical system with a finite number of degrees of freedom. Its (second order) dynamical equations can be gathered in a matrix equation $$M\ddot X + K X=0$$ ...