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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How can we theoretically calculate the number of balloons needed to stop a bullet?

After watching this video, I am interested in proving it mathematically. The problem is that how can we apply the conservation of momentum here to find the velocity of the bullet while we don't know ...
3
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2answers
130 views

Why does General Relativity predict more light deflection than Netwonian Physics?

If one looks at the limit as light's mass approaches zero, Newtonian Physics predicts a deflection of light (this can be seen by the fact that all objects are accelerate the same due to gravity.) ...
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2answers
166 views

Polar moment of inertia of a cylinder

So I know the polar moment of inertia of a solid cylinder is: $$ I= \frac{1}{2} mr^2 $$ My question arises with the polar moment of inertia uses for solid cylinders in my mechanics of materials book, ...
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1answer
579 views

Bowling Ball Sinking Rate - Variable or Constant?

In today's (Jan. 16, 2014) xkcd What If?, Randall Munroe discusses how fast a bowling ball will sink to the bottom of the Mariana Trench. He calculates the drag on the ball, and then plugging in the ...
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1answer
157 views

Solving the Kepler problem

I'm trying to solve the Kepler problem using the Lagrangian, $$L = \frac{1}{2} m (\dot{r}^2 + r^2 \dot{\phi}^2) - U(r) $$ which after quite a bit of fiddling with, by noting that the angular ...
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0answers
144 views

Relative velocity between a ball hitting a rod [closed]

A ball of mass $m$ travelling with a velocity $v_0$ collides elastically, and perpendicularly with a rod at a distance $d$ from the center of the rod. The rod has a mass $M$ and lies on a frictionless ...
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1answer
423 views

Conservation of angular momentum in a free rod

When a collision is elastic and no external torque acts on a system, angular momentum is conserved I found this example and checked the results: A ball (m = 1 Kg , v = p =+22 m/s, Lm = +11, Ke = 242 ...
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0answers
33 views

Obtaining angular velocity of a general orbit

Provided you are given a effective potential function i.e. $$ V_{eff}=\dfrac{J^2}{2ml^2sin^2(\theta)} + mgl(1-cos(\theta))$$ how do you obtain the angular velocity for different types of orbits; i.e. ...
2
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1answer
167 views

Shouldn't motion be represented as a Taylor series rather than a finite sum of functions or a polynomial? [closed]

Since the change in velocity of an object at rest prior to time $t_{0}$ implies a change in acceleration — that is, let's postulate, $ \mathbb{P} $, the object would have remained still, so there was ...
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3answers
1k views

How hard would I hit the ground on Mars?

How do you calculate with how much force a mass would hit the ground when falling from a certain height? In particular, I'm curious to know how the force of impact on Earth compares with Mars, so ...
4
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2answers
624 views

Why do your fingers alternate then meet at the center of mass of the object?

Hold a pen (or pencil, ruler etc.) using your two index fingers with your fingers at the ends of the object. Now move your two fingers toward each other. Assuming the frictional force provided by both ...
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1answer
55 views

Period of oscillation with time independent factor

How can you determine the period of oscillation from a mass that is suspended from the ceiling? The equation becomes: ${{d^2x}\over dt^2}+kx-mg=0$. I am confused by the constant $mg$, because in the ...
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2answers
1k views

What will be the equation of motion of driven pendulum for amplitudes beyond the small angle approximation?

When finding the period of a pendulum beyond the small angle approximation, we have to use integration for small interval of $\theta$ and elliptical integration. I was trying to apply this situation ...
0
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1answer
368 views

Find center of mass and moment applied on beam structure [closed]

I have a simple physics problem to solve but it is giving me a slightly difficult time to figure out. The problem: I have a beam structure with same cross section. It consists of three beam. First ...
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0answers
134 views

Instantaneous acceleration in non uniform circular motion

How is instantaneous acceleration different from tangential acceleration in a non uniform circular motion? We know that instantaneous acceleration is tangent to a point at any given time and so is ...
3
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3answers
360 views

Why does reduced mass help when talking about two body problems?

I hear people say that reduced mass, $\mu$, is used for two body problems, but what sort of problems? Is it so that the two body system can be treated as one body or is it to simplify calculations ...
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1answer
226 views

Momentum and Kinetic Energy Conservation in Inelastic Collision

Let a ball fall freely to the ground, hit and bounce back. Assume mass of the ball does not change during this. Since momentum is conserved in all collisions, $p_i = p_f$ In this example, the system ...
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5answers
3k views

As a car turns around a circle, why does the force of static friction point towards the center of the circle [duplicate]

A car moves along a flat, circular road. It has a tangential velocity to the road, but the car tires change direction and the car experiences a force of static friction causing a centripetal ...
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0answers
36 views

Rocket in constant gravitational field [duplicate]

A Rocket in a constant gravitational field, what are the conditions required for the rocket to take off immediately? (in terms of $m_0,μ,g,v_r$), where $m_0$ = mass of the rocket at $t=0$ $μ$ = mass ...
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4answers
351 views

What position of the center of gravity can make the front wheels of the car lift off the ground?

I have a question regarding the position of center of gravity required to just lift off the front wheel of a vehicle Consider a vehicle of mass $m$ having a center of gravity at height $h = 0.5m$ ...
1
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1answer
359 views

How does the space shuttle move in a vacuum? [duplicate]

If there is no friction in space, then how does the space shuttle boost? According to Newton's law we move by pushing something; in space, there is vacuum, so how the space shuttle moves without ...
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2answers
142 views

How to find a condition that ensures that the rocket immediately takes off?

For the rocket in a constant gravitational field, how to find a condition that ensures that the rocket immediately takes off? Update: I apologize. Let's try again. So my question: For the rocket in ...
0
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2answers
54 views

Why normal doesn't do any work in this case

Suppose the stick slides without friction along flat surface. Why in this case N does not do any work? As i see stick not only slides in horizontal direction, but also falls in vertical direction, ...
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3answers
3k views

Stretch length of horizontal and vertical springs

If the spring in Figure A is stretched a distance d, how far will the spring in Figure B stretch? The spring constants are the same. The answer is "by half". I don't get it, to me it's the same.
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3answers
351 views

Show bigger amplitude of physical pendulum means bigger period

Suppose you have a physical pendulum. It is true that as amplitude increases, the period increases. Can we demonstrate this fact without explicitly finding the period (which is pretty involved and ...
2
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1answer
123 views

More accurate version of Newton's Second Law?

Since Force is a one-form (co-variant vector), is it more accurate to assert that $F = ma^ug_{uv}$ where $a^u$ is the acceleration vector, which is contra-variant, and $g_{uv}$ is the metric tensor?
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2answers
238 views

A big cannon to match a ballistic missile? [closed]

During the last years of WW2 the Germans used ballistic missiles V-2 (with payload mass ~1,000 kg) to bombard London, from a distance about 300 km away. Suppose the British could respond by building a ...
0
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1answer
80 views

a mistake related to variable mass system

I'm having a problem with finding my mistake when trying to find the derivative of the momentum when mass is being ejected in a constant rate. The problem is this - a body in space is burning fuel ...
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4answers
654 views

Spring stiffness calculation problems

I am trying to model a 1 DoF electromagnetic vibration sensor (geophone) analytically and with finite elements. A geophone consists of springs, a permanent magnet and coils. The coils are suspended ...
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2answers
1k views

If an object falls - regarding air resistance - does the Potential or Kinetic energy get converted into thermal energy as it is falling?

I read a paragraph on the transfer of potential energy to kinetic energy and heat from this website: Even if air resistance slows down the ball, the potential energy is the same (Mb x g x H). ...
0
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2answers
370 views

Calculation of tension in a loop with force acting outwards

I'm having a few problems with understanding how to calculate tension in a loop. If I have a circular loop, and some force is applied uniformly radially outwards in such a way that the force acting ...
3
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3answers
896 views

Is the shell theorem only an approximation?

I've read the shell theorem during gravitation lectures, i.e. I know it states that the net gravitational field inside a 3D spherical shell or a uniform 2D ring is zero. Now, assume a thin spherical ...
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4answers
283 views

Which is the right explanation for rocket motion? [duplicate]

What actually causes a rocket to move? Is it the pressure in the rocket engine or the amount and velocity of mass that is being ejected out. The reason I am asking is, I found these two explanations ...
2
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2answers
380 views

Is gravitation really a conservative force?

A rotating gyroscope that is mounted in a gimbal maintains its rotational axis relative to space when it is moved – and not to the surface of the earth, as illustrated below (the figure shows only the ...
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1answer
99 views

How do I do non constant acceleration questions?

Okay, so there is a type of question that keeps coming up in past papers and I can't seem to crack it. The one I'm doing now is: A skier initially travelling at $50~\text{m/s}$ along a ...
0
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1answer
321 views

Tension on strings holding a weight [closed]

It's a 100% standard problem in any basic physics course, and I cannot solve it. Here's the scenario: What is the tension in the strings (T1 and T2)? My thoughts were (cos/sin rewritten as ...
0
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1answer
33 views

Stiffness of a suspension

I think It is a trivial question from the point of view of engineering. But I am curious. Suppose you have to make a suspension. A less stiff spring will not do the job. It would just slide over. An ...
0
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2answers
260 views

Orbital mechanics problem

Here is a problem from the 2009 $F=ma$ contest on orbital mechanics: Two stars, one of mass $M$, the other of mass $3M$, orbit their common center of mass. When the stars are collinear with the ...
0
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3answers
124 views

Reason for motion after terminal velocity

Let some object hang by a string. So no motion since weight was counter balanced no net force. Now string is cut. Object is falling under gravity and experiences air resistance. Terminal velocity is ...
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2answers
404 views

Dumbbell rotation

What if apply impulse to dumbbell consisting of two masses and massless rod? It is clear for me that left dumbbell will move straight line. But it is not clear for me what kind of motion will have ...
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2answers
248 views

Torque at a disc sandwiched between two rotating discs

I have a question in my mind regarding torque transfer taking place in the current situation. There are three rotation elements A, B & C as shown in the figure. The rotating element A is ...
0
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1answer
38 views

Collar on a rim in a vertical frame [closed]

Suppose we have such construction as shown at the picture. The vertical frame starts from rest with constant acceleration $a.$ Find final angle $\theta,$ assuming no friction. Also plot $\dot\theta$ ...
1
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1answer
73 views

Space and motion

When we throw a ball upwards sitting in a running bus or train it directly comes to our hands but when we do the same sitting on a moving motorcycle the ball falls backwards. Why?
2
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2answers
126 views

Can the epicycles of the geocentric model of the solar system be dismissed due to the laws of physics?

With enough epicycles, the motions of the planets can be accounted for in a geocentric model, but do the laws of gravity make such motions impossible? Did Newton's laws not only provide a simpler ...
3
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2answers
198 views

Does the outflowing water create a thrust on the bucket?

Let's consider the the bucket with water, which has a small hole at the bottom. Let the bucket lift up with a constant force $\vec F$. Water in the bucket, of course, flows out of it. Questions are ...
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0answers
135 views

Reduced Three-body problem

I know that three-body problem in celestial mechanics can't be solved analytically in general. But suppose that the 3rd body is much smaller than the others, so it does not perturb their orbits. This ...
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2answers
123 views

Newton's Principia: Astronomical prerequisites?

I am planning to read the Principia but I currently have no knowledge about Astronomy. What astronomy prerequisites do I need to understand the Principia? I would prefer older books (or "treatises"), ...
2
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2answers
101 views

Is It Possible To Move The Earth In A Direction? [duplicate]

According to Newton's 3rd law, when an object moves upward, the Earth moves by a very tiny factor in the opposite of the direction of the object. And when the object falls back, the earth moves back ...
3
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2answers
122 views

Can momentum be distributed to multiple objects which travel in different vectors?

This is a question about the conservation of momentum: If there were a cluster of billiard balls floating in space and the cluster was struck by one moving ball, the cluster balls would scatter in ...
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0answers
3k views

Solve for one unknown mass in a simple pulley system [closed]

My class was given a problem where we would use a pulley system to calculate the mass of a pair of car keys. We attached 200g weights to each side of a pulley system and attached the keys to one of ...