# Tag Info

19

It does. The fact that it is in contact with the earth (or rather, the rails), just means that it cannot move sideways under the force, because the rail restrict its movement. In the same way, if a train travels down a rail and has wind blowing from one side, there is still a force pushing it, but the rails will exert an opposite force so it can't be moved ...

5

Soft sand deforms when you step on it. The force applied by your foot to the sand moves through the deformation distance, performing work on the sand which your muscles provide. That work does not assist your propulsion; it is lost to the sand. The sleek flat floor does not deform when you walk on it and therefore does not "steal" work from you as ...

5

If you recall the Coriolis force given by $$\mathbf{F}=-2m\mathbf{\Omega} \times \mathbf{v}$$ If for a minute, We don't get into the detail of the analysis but just see the magnitude of this. $$|\mathbf{F}|=2m|\mathbf{\Omega}_\text{earth}||\mathbf{v}_\text{train}|$$ Let's take the speed of the train to be $100$ Km/Hour which is about $30$ m/sec and mass to ...

4

By resolving it's doesn't mean that it's sort of resultant of $u$ and $w$ because $uw$ are used as axis. You should say one can write $\mathbf{F}$ as linear combination of component along $u$ and $w$ so that $$\mathbf{F}=F_u\hat{u}+F_w\hat{w}$$ where $\hat{u}$ and $\hat{w}$ are unit vector along these axis.

3

What is the value of acceleration when the string breaks? The string will break when the tension in string reaches the tensile limit say ($T_0$).The tension in string for given acceleration can be calculated easily from FBDs. Why does not the ball stays fixed in its initial position forever, so that the tension becomes high in the string, and it eventually ...

3

No, we cannot. In fact, the claim is not even true. Bodies do not fall with constant acceleration. The gravitational force decreases with the distance squared, so as the body falls its acceleration increases, if only a bit. Plus, there is air friction, etc. If the falling distance is short enough that you can neglect the dependence of the gravitational force ...

3

Assume the object hangs vertically before the bus starts to accelerate. When the bus starts to accelerate there is instantaneous relative movement of the object relative to the bus seen by observers both on the bus and on the ground. To the observer on the bus, the bus is not moving and the object moves due to the fictitious force present in the accelerating ...

2

This is a very interesting question, because I think I see what your thinking is in this - you are imagining the field lines as acting like tiny threads of elastic material, that have tension in them so they exert forces upon each end, and the electric force between two charges is the sum-total of all these little tensions created by each field line thread, ...

2

My question, is there any research on this area? The accepted main stream physics is that nothing goes faster than the speed of light. This has been accepted as an axiom because it has been verified in a huge number of experiments. The force you envisage is composed of electromagnetic forces transferred atom by atom on a rigid arm, and electromagnetic ...

2

Since the two masses aren't connected via friction or using another medium (such as a lead or a spring), hence you can't consider the two masses as a unique mass (or as a system of connected body). Every mass has to be considered separate from the other ones. So the equation that holds for this situation is, as you wrote: $$\vec{F} = M_1 \vec{a}$$ which you ...

2

At a glance the setup in Richard Myer's answer seems correct, but there are a couple of errors. That the net torque on the system is zero (the body as a whole is not rotating) amounts to a single equation --- if one examines them closely, the condition that the torque about the feet is zero should be identical to the condition that the torque about the ...

2

First case you have: $$T=\frac 12 M\,v^2+\frac 12 I\omega^2=F\,L$$ with : $$v=\omega\,R~,I=\frac 12 M\,R^2$$ you obtain $$\omega=\frac{2}{3}\frac{\sqrt{3}}{R}\,\sqrt{\frac{F\,L}{M}}$$ second case $$T=\frac 12 M\,v^2+\frac 12 I\omega^2=F\,L+F\,R\,\varphi$$ with $$\varphi=\frac{x}{R}=\frac{L}{R} \,,v=\omega\,R$$ you obtain  \omega=\frac{2}{3}\frac{\sqrt{6}}{...

2

Your first approach is wrong. You assume that the work is $F\cdot S$, which is only valid iff $F$ is a constant force. However, the force that satisfies your scenario is not constant. The easiest way to show this would be take the negative gradient of the potential energy which gives the force. If you haven't learned this, then you can try solving for the ...

2

There are many good and insightful answers here, but I will just add one thing. As stated, the answer to this question is, of course, emphatically no. But I want to come at it a little more from the angle of what relativity actually tells us. First of all, Galilean relativity is not capable of telling us anything about the acceleration at all, except that ...

2

While the science of physics has led to explanations for a lot of phenomena, there are things that have to be assumed as is in order to frame a theory at all. To give context to what I want to say, let me discuss the concept of 'level of description'. In physics a breakthrough moves the level of description to a deeper level. Example: Kepler had formulated ...

2

There is no way to calculate inertia numerically since inertia is not quantitative property, instead it is a non-numerical qualitative property of an object. We can say that the more mass an object has then the more inertia it has and vice-versa. So the amount of mass an object has can be an indicator of how much inertia it has, or how much it will resist ...

1

*@Eisenstein You're asking why things can be moved at all from some ordained position. – jpf @jpf In a nutshell yup. – Eisenstein* It seems physics has offered the best answer that it can with regard to a questions of attaching a number to the concept we call inertia (the proportionality constant we call mass that results in an equality in a force and ...

1

According to relativity, the mass (which is the quantitative analogy of inertia: the higher an object's mass, the harder it is to accelerate it under the influence of a force) attached to a spring in an accelerated frame is equivalent to a spring hanging in a gravity field. Objects in this gravity field will experience the same acceleration as the ...

1

You can firstly think about this scenario without the earth at all. Let's say you have a rocket in free space. A chemical reaction inside the rocket can cause a force $\vec{T}$, which acts on the exhaust material and it will be directed downwards, away from the rocket as you showed. Newton's third law tells you then that there will be an equally large but ...

1

The $r$ value in this equation represents the separation of the two bodies' centers of mass. So, when you're standing on the surface of the earth, then the value of $r$ is equal to $r_E$, the radius of the earth, which is $6378$km or $6.378\times10^{3}$m. To answer your more general question, the force between two masses does, indeed, increase as separation ...

1

Because of Newton’s third law, for every action there is an equal but opposite reaction. When your feet push on the ground, the ground pushes back. The force that your foot exerts on a flat ground is mainly determined by friction. The higher the friction, the more efficiently you can walk. If the frictional force is decreased, the harder it will be to walk. ...

1

Walking is applying force on an object and, that object keeping the same approximate location, being propelled in return in the opposite direction. If said object is mobile, like a box on a slippery floor, when you push it it will move and offer no resistance. This resistance is what makes walking possible. This is why sand or, worse, water, are not ideal to ...

1

A force as an external influence or action on an object that causes the object to change velocity, that is, to accelerate relative to an inertial reference frame. Newton’s second-law statement, like Newton’s first–law statement, can be applied only in inertial reference frames (Galilean invariance). Newton's second law states: The acceleration of an object ...

1

The system is the lift and so you must count all forces acting on the lift which are: gravitational attraction of the Earth downwards, $540g$, normal contact force due to man standing on lift downwards, $70g$ tension force due to cable upwards, $540g+70g$. The assumption is that the lift and man are at rest or are moving with constant velocity.

1

The most common approach is to keep track of the position, velocity and force components (as in X,Y directions) as well as the orientation angle of the object. It is important to understand that you need to track the center of mass of each object. The at each time step calculate the acceleration components and increment the velocities first and the position ...

1

The difference between boucing and less bouncing objects is how the kinetic energy is dissipated. The impact of a solid object in the ground can be divided in 2 steps. At first, there is a quickly increase of the compressive stress in the region of contact as the ball decelerates. A short fraction of second after the impact, the ball is at rest, but under ...

1

So, if I take a rope, 'fold' it over something to redirect it and then load both strands in the same direction with a certain force, each Strand of the rope should See 50% of the tension, right? Each strand would see 50% of the tension that would have been if a single strand was used. So, tension in each strand would be F/2 where F is the weight / force ...

1

There are three forces on the door: gravity $\vec F_g$, the applied force $\vec F_a$, and the constraining force from the door hinges $\vec F_h$. $\vec F_g + \vec F_a + \vec F_h = m\vec a$ where $a$ is the acceleration of the center of mass (CM) of the door and $m$ is the mass of the door. The component of the hinge force in the vertical direction ...

1

The weight of the object makes the table deflect (bend) slightly. This stretches the inter-molecular bonds in the table. The inter-molecular bonds resist the deflection, and this gives rise to the normal force exerted by the table on the object. However, the inter-molecular bonds have a finite strength, and if they are stretched too much they will break, and ...

1

An interesting question that deserves an interesting answer! Galilean relativity: the laws of motion are the same in all inertial frames. The trick here is in defining a limited reference frame. Practically speaking within a limited reference frame we cannot determine whether we are moving or staying at rest. For example, two skydivers exit an aircraft at ...

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