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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Is energy “destroyed” when walking?

Conservation of energy states energy can't be destroyed, but isn't energy used up when walking in a straight line? If your not walking up a slope, kinetic energy isn't converted to gravitational ...
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When should we use the concept of Impulse/Momentum instead of Force?

In my notes it says "The ideas of impulse and momentum is useful in solving problems where:- a) the force F is not easily calculable (e.g. sudden impact or blow) b) the impulse force is ...
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292 views

Could someone remind me what this means again? $\nabla U = \pm F$

You know that for a potential function (conservative force/fields) that $\nabla U = \pm \vec{F}$ In math, we don't have that minus sign, we have only the plus one. What does it mean if you get rid ...
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2k views

How do I properly use Newton's Third Law and Free Body Diagrams?

A force of 14.0N is applied to a block as shown in the diagram below ! If the coefficient of friction is between the surface and the blocks is 0.35 a) What is the acceleration of the two blocks? b)...
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I think there is something wrong with this problem. How do you know if the vertical acceleration is zero?

Suppose a block with mass 3kg is on a frictionless table and a force of 15N pulls it from an angle of 38 degrees above the horizontal. 1) What is the apparent weight of the block? 2) What is the ...
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128 views

Would a projectile keep going forever in empty space?

Would a projectile fired in space and assuming there were no stars or planets in the way, would the projectile continue on to infinity, since the x-component of the projectile's velocity never changes ...
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998 views

What is a Free Body Diagram?

I have this problem: A 10 kg box is resting on a frictionless table and someone drags it by a string at a 30 degree angle to the horizontal with a force of 40 Newtons. Find the acceleration of the ...
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50 views

What is the degree of freedom of pure rolling motion?

A cylindrical body is pure rolling, what will be the degree of freedom for it? I am confused between 2 and 1 if slipping occurs than it has 2 but in pure rolling there's no slipping so what will it ...
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41 views

Point object, Kinematics

I am very new to physics. This evening, I was reading about the concept of objects to be considered as point objects under some circumstances. And I was trying to think of circumstances under which ...
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120 views

Why are trains so hard to stop?

Since there are brakes on every car, shouldn't the stopping time of the entire train be the same as the stopping time of a single car? Is this because the cars themselves take a long time to stop, or ...
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49 views

System rigidity

What is the meaning of system rigidity in mechanics? I can't understand how to classify the system as rigid or not, and what is the effect of rigidity on the whole system. If you know anything about ...
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49 views

Conservative force for impulse analogous to conservative force for work done?

As force $F(x)$ can be conservative regarding work done between two points in space, can force $F(t)$ be conservative regarding impulse between two points in time?
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63 views

How is frictional force dependent on normal reaction?

It is a general concept that horizontal forces can only influence physical quantities along horizontal direction; similarly vertical force can produce acceleration etc. only along vertical direction. ...
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54 views

Question about levers

Suppose we have a lever $AB$ of length $1m$ and that the fixed point is $O$ and $AO=0,3m$. If in $B$ I have a down vertical force of $F_1=5N$, find the force $F_2$ applied in A that guarantees the ...
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42 views

Accelerations of Cylinders

I got a box hanging from a rope that passes through an ideal pulley that attaches to the superior part of a Cilynder and makes it rotate. An exercise asks me two things: a) determine the magnitude of ...
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33 views

Velocity over time applying constant power and considering air drag

I wanted to understand how velocity changes over time when applying a constant power to a body of mass $m$. I figured out that in this case, since $$P=d/dt(KE)=d/dt(\frac{1}{2}mv^2),$$ integrating I ...
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46 views

Ball rolling down an incline and dynamics in general

I recently performed an experiment for a class which involved measuring the projectile motion of a ball after it had rolled down a ramp and exited on a significantly smaller ramp. When interpreting ...
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79 views

How do we define what is “External” force or “Internal” force in the context of momentum conservation?

I know that without presence of any "External" force momentum is always conserved. But how do we distinguish between "External" force and "Internal" force where all are "Force"?
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69 views

Dynamics of two pulleys [closed]

I have been trying to do this exercise for 2 days but I'm sure that I'm negleting something... Here is the sketch of the situation: $$m_A= 4M \\ m_B= M \\ m_C=2M$$ All the strings cannot ...
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61 views

Why an impact exerts so much force? [closed]

If an object of velocity $v$ and mass $m$ moves towards a resting object of mass $M$, then if the object which is hit might break. Why? What is the reason that a collision has more power than a ...
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88 views

Centripetal force: if radius decreases, does ANGULAR or TANGENTIAL velocity change?

Having conceptual trouble with this aspect of centripetal force. Say we have a puck on a frictionless table attached to a string that I am holding through a small hole, so that the puck moves in a ...
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58 views

How can an accelerating inclined plane prevent a block on it from sliding?

If I increase the force $F$, only the normal force $N1$ acting on $m1$ would increase which has no component along the plane, ie. along $m1gsin\theta$, so how would applying this force prevent m1 from ...
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51 views

Finding inclined plane acceleration

In the above diagram, both the surfaces are frictionless. The force exerted by $m_1$ perpendicular to the inclined plane $m_2$'s surface is $m_1g\cos\theta$, and the horizontal component of that force ...
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77 views

Tension and friction. Cool question

I had an exercise like the image, where block A is pulled by a force F, there is that rope(tension) attached to the block B and the wall, and there is friction between A and B, and A and the ground, ...
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38 views

Relationship Gravitational Potential and the Tangential Velocity of a Satellite

So gravitational potential is given by $V(r)={\frac{GM}{r}}$ and the tangential velocity of a satellite is the square root of $V$, i.e. $\sqrt V$. So how do these two relate, if at all?
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75 views

How is a mass, suspended vertically by two springs in parallel, kept stable? [closed]

Consider a mass suspended vertically from above by two springs in parallel with different spring constants. Wouldn't the tension be different in each spring? How is this system kept in equilibrium?
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49 views

Amplitude of damped driven harmonic oscillator [closed]

I have a question that I can reason physically but mathematically I am not sure if my approach is correct. The amplitude of the oscillator is: $$A(\omega) = \frac{QF_{0}}{m}(\frac{1}{\omega_{0} \...
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97 views

Spinning a string with a mass on the end. What makes the mass rotate parallel to the ground? [closed]

Say you use your hand to rotate a string with a mass attached to the end. The string will first become taunt and then the mass and string will move upwards until they are spinning parallel to the ...
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1answer
46 views

What is the translational velocity of a sphere after rolling down a hill?

A solid, uniform, spherical boulder starts from rest and rolls down a 50.0-m-high hill. The top half of the hill is rough enough to cause the boulder to roll without slipping, but the lower half is ...
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62 views

Definition of translational , rotational , rolling motion

What are the exact definitions of pure translational , pure rotational and rolling motion ? I am a class 11th student ... I find it difficult to exactly make a difference between translational , ...
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73 views

What Feynman meant in description of reversible machine and levers

In chapter four of the part one of the lectures, he mentions: (..) A machine that we actually use can be, in a sense, almost reversible: that is, if it will lift the weight of three by lowering ...
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38 views

In rotating frames, particles do not travel at constant velocity?

If we measure a particle's trajectory in a rotating frame of reference as $\vec x=\vec x(t)$, then $\frac{d^2\vec x}{dt^2}=0$ could be zero? I'm trying to explain why the Newton's first law of ...
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31 views

How can you calculate the thrust-to-weight ratio of a gun?

Is there some formula I can apply to the weight of a gun, along with the force of thrust it creates, and calculate if it will be able to lift itself off the ground or not? Without actually handling ...
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116 views

Difference between potential centrifugal energy and rotational/kinetic energy

I'm having troubles to understand the difference between kinetic energy and potential centrifugal energy in some situations. I make an example where I am confused. A object moves on a rod attached ...
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67 views

Free falling and bouncing back

My confusion arises with free falling body. For a free falling body the displacement ~ time graph has a kink (at the time when the body hit the ground ). at a kink point, a function is not ...
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1answer
77 views

How does friction affect the motion of a pendulum?

I would like to know what is the difference in the equation of motion of a pendulum in the presence or the absence of frictional forces. And how this translates to the solution of those equations?
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113 views

Forces on wheels in an accelerating vehicle

Assume that a motorcycle of mass $m$ has two wheels that are equidistant from its centre i.e the force on each wheel is $mg/2$. If the motorcycle accelerates forward, will the two forces on each ...
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68 views

What does well defined parity mean

I'm reading a textbook (Physics of Quantum Mechanics by Binney) and it says that the ground state ket $\left\lvert 1 0 0 \right \rangle$ of the hydrogen atom has well defined (even) parity. What does ...
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50 views

Interpreting force components in statics problems involving inclined planes or similar

I'm having troubles to understand how to interpret the components of forces on inclined plane in quite complicated situations. I will make an example of one of the cases where I get confused. ...
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86 views

Why is work a scalar quantity?

If the displacement is in the direction of the force, then work is positive. If the displacement is in the opposite direction of the force, then work is negative. If the displacement is perpendicular ...
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1answer
47 views

Center of mass of an arc

A very thin tube shaped like a quarter of a toroid has one end attached to the origin $(0,0,0)$ and the other end at $(R,0,R)$. Determine its center of mass. So obviously $y_G = 0$. Using Pappus ...
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79 views

Can a submarine be powered by a wind turbine?

This is not intended as a realistic way for propulsion of submarines, it is just an interesting thought experiment. Say I want to travel directly towards the wind, only powered by the wind. This is ...
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1answer
31 views

Applicable force at constant velocity [closed]

For a body moving at a constant velocity, the force $F_{net}=ma$ Since acceleration is 0, $F_{net}=0$ (i.e force applied = resisting force) Since force applied and resisting force are equal, will ...
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49 views

Does a capacitor experience a Newtonian reaction when being charged?

Say I have a capacitor that is being charged with a battery. There are two wires, one on the positive and one on negative terminal of the battery which go to a capacitor. During the charging, a ...
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43 views

Static Equilibrium [closed]

A 3 Newton force and a 4 Newton force are acting concurrently on a point. Which force could not produce equilibrium with these two forces? 1N 7N 9N 4N I'm confused. The book I'm looking at says ...
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1answer
53 views

Calculating post-collision velocity [closed]

Consider two persons $p1$ and $p2$ of the same mass , such that they are together moving rightward with a velocity of $v/2$ Now person $p1$ pushes $p2$ in the left direction. According to newton's ...
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96 views

When a ball bounces on a wall at an angle, why does the angle of incidence equal angle of reflection?

When a ball is thrown to a wall without spin and bounces, supposing it's an elastic collision, why does the angle of incidence equal the angle "reflection" (relatively to the normal), why isn't it any ...
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118 views

Motion of an object in a moving car and collison

I came across an interesting question today at work. 'Imagine traveling in a car. The passenger has a glass bottle in their hand. In which direction relative to the moving car should the passenger ...
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92 views

conservation of momentum? [closed]

At hyperphysics I got this image, with the same description in text as is in this image It says that when a massive particle (say $A$) moving with a velocity collides with an object having a ...
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48 views

A question on Jeans's instability

I am a Physics student and I'd really appreciate if anybody could help me with an exercise my professor gave me a couple of weeks ago. It goes like this: Let us consider a spherical symmetrical gas ...