I just finished my class on circular acceleration and I learnt that centrifugal force (outward force) is a psuedo force. It doesn't really exist.   Now suppose I am going round in my car or a merry go round or whatever. I feel like a force is pushing me from the center and towards the window of my car which is in the opposite direction from center. Now how this be explained?   I asked this to my teacher but he gave an explanation with inertial reference frame which I didn't really understand.   Pardon my grammatical and spelling mistakes.
40978
Currently in my last year of high school, and I have always been told that  does not exist by my physics teachers. Today my girlfriend in the year below asked me what centrifugal force was, I told her it didn't exist, and then she told me her textbook said it did, and defined it as "The apparent force experienced towards the outside of a circle is the centrifugal force and is due to the mass of the object resisting the inward centripetal acceleration that the object is experiencing". I was pretty shocked to hear this after a few years of being told that it does not exist.  I did some reading and found out all sorts of things about pseudo forces and reference frames. I was wondering if someone could please explain to me what is going on? Is it wrong to say that centrifugal force does not exist?   This has always nagged me a bit as I often wonder that if every force has a reaction force then a centripetal force must have a reaction centrifugal force, but when I asked my teachers about this they told me that centrifugal force does not exist.
6794
They say that gravity is technically not a real force and that it's caused by objects traveling a straight path through curved space, and that space becomes curved by mass, giving the illusion of a force of gravity.  That makes perfect sense for planetary orbits, but a lot less sense for the expression of gravity that we are the most familiar with in our day-to-day lives: "what goes up must come down."  Imagine that I hold a ball in my hand, several feet off the ground, with my fingers curled around it, and my hand is above the ball.  Then I open my fingers, releasing my grip on it, being very careful to not impart any momentum to the ball from my hand as I do so.  An object at rest remains at rest unless acted upon by an outside force.  If the ball is not moving (relative to my inertial reference frame), it has no path to travel that's any different from the Earth's path through space.  It should remain at rest, hanging there in the air.  And yet it falls, demonstrating that an outside force (gravity) did indeed act upon it.  How does curved space explain this?
46263
Suppose there's a force $F$ of magnitude 10 newtons in the direction of positive y-axis acting on a particle A. I know that the particle would not experience any force in the positive x-direction because,  component of force $F$ in the positive x-direction $=|F|cos90°=0$.   But if we first take the component of $F$ at an angle of 45° to the positive y-axis, it is,   $|F|cos45°=\frac{10}{\sqrt2}\text N$.   If we now consider this a vector (can we? that is the main question), we can find its component in the positive x-direction (it makes an angle of 45° with the positive x-axis) ,   $\frac{10}{\sqrt2}\times cos45°=5\text N$. According to this result, the particle should experience a force of 5 newtons in the positive x-direction, which is impossible. I want to know what all is wrong in the above reasoning. Thanks!
83852
When I am on earth, the weight of my body is countered by the reaction of the ground. So, there is no net force acting on me.  But I am spinning with earth. But if there is no centripetal force then why am I spinning? And the equal air pressure on both side of my body won't be enough for me to stay in the same angular velocity as the earth.  Is it just conservation of angular momentum?
28508
Fundamentally, what does a friction force do for a rolling object? I am very confused by the way my textbook explains it. In my textbook , it says:  A wheel rolling on a horizontal flat surface at a constant velocity experiences no friction force. Why?   On the same surface, there is an acceleration of the wheel pointing to the right (probably caused by a force), so the ball is angularly accelerating in the clockwise direction. In this case, a friction force appears, and it is also pointing to the right. How come? What does the friction do for this wheel?  On an inclined plane, a ball freely rolls down the surface. The direction of friction is up the ramp, which confuses me because in the previous example the friction force was in the direction of the wheel's acceleration.   And there is a difference if a wheel is freely rolling and if there is a torque acting on the ball's center of mass. WHY???  What does friction do in these cases? How does it cause an object to roll?
7117
When I'm rotating, I feel centrifugal force. But if I were the only one in the universe and rotating, wouldn't I just kinda be still (since I'm not rotating with respect to anything) or would there just be a force pulling me out? What if there were another person a billion miles away, this should not change anything, right?
62225
On , it is written that      So, we see things falling with an acceleration which we call the acceleration of gravity,and thinking that we live in a straight line , uniformly moving or stationary inertial frame, we attribute that acceleration to a force, the force of gravity. Whereas in reality,objects falling towards the Earth are moving along geodesic paths with no acceleration and according to modified version of law of inertia, have no force acting on them. They fall simply because the curved space-time near the Earth ...   Now, why do the objects falling towards the Earth move along the geodesic paths with no acceleration? That means the objects don't have any force acting on them, but why? A body in a free-fall moves with acceleration $g$, so, why is it written like that? Why does the author use Law of inertia on freely falling body?? Law of Inertia can only be applied when no external force acts on the body. So, is the freely-falling body accelerates under force of gravity or moves uniformly while moving through geodesic paths as quoted by the author?
99726
We often see films with spinning space station that create  by having the astronauts pulled outwards by centrifugal force.  I'd like to know if this would really happen, and if so, why is the following scenario not true:   Take an astronaut in open space. He doesn't move. Put a big open spinning cylinder around him - surely he still doesn't move. Close the cylinder. I still see no reason for him to be pulled outwards.
67918
I am studying angular momentum and I get the concept that it has a meaning or it is defined only with respect to a  certain point (often called as origin). I was looking at the realtionship between torque and angular momentum around an origin i.e.  net torque  = Rate of change of angular momentum (equation 11.29 in the picture). I think i get this relationship. Where I got confused when author adds a caution (full quote below) to the equation saying that:  If the center of mass of the system is not accelerating relative to an inertial frame, that origin can be any point.  However, if it is accelerating, then it must be the origin.  I am not sure if I get that statement and caution.  Not sure what the author means by the “origin” here.  Can't the origin be any point that we choose?   Let $\vec{\tau}_{\mathrm{net}}$ represent the net external torque, the vector sum of all external torques on all particles in the system.  Then we can write Eq. 11-28 as \begin{equation}   \vec{\tau}_{\mathrm{net}} = \frac{d \vec{L}} {dt} \qquad \text{(system of particles)} \tag{11-29} \end{equation} which is Newton's second law in angular form.  It says  The net external torque $\vec{\tau}_{\mathrm{net}}$ acting on a system of particles is equal to the time rate of change of the system's total angular momentum $\vec{L}$.  Eq. 11.29 is analogous to $\vec{F}_{\mathrm{net}} = d\vec{P}/dt$ (Eq. 9-27) but requires extra caution: Torques and the system's angular momentum must be measured relative to the same origin.  If the center of mass of the system is not accelerating relative to an inertial frame, that origin can be any point.  However, if it is accelerating, then it must be the origin.  For example, consider a wheel as the system of particles.  If it is rotating about an axis that is fixed relative to the ground, then the origin for applying Eq. 11-29 can be any point that is stationary relative to the ground. However, if it is rotating about an axis that is accelerating (such as when the wheel rolls down a ramp), then the origin can be only at its center of mass.
35747
In a non-inertial reference frame, the centripetal force is balanced by a centrifugal force. Therefore, shouldn't the net acceleration be zero? Yet, you still feel an acceleration outwards? Why is that?
116339
What is the cause of / force? When an object of mass $m$ is moved in a circular orbit, it experiences a centrifugal force radially away from the center. What is the cause of this centrifugal force? Is these related to the four fundamental forces (gravity,electromagnetic,weak and strong forces)?  This force is equivalent to a force experienced while stopping a mass in motion (Inertia).  But is this inertia caused by some force? or what causes inertia? A photon particle does not have inertia of rest.
120616
I used to think that torque and force were equally “fundamental”. In other words, my understanding was that we usually use Cartesian coordinates in many common problems because it is a convenient system, so as a result instantaneous forces which act in straight lines seem “easier” mathematically but torques require some extra “baggage”. This baggage includes typically teaching that torque is defined in terms of force.  But if say we happened to choose polar coordinates for the problem the situation would appear the other way around. So it would be arbitrary if we chose to define forces in terms of torques instead.  But later on I learned that angular momentum is conserved independently of regular linear momentum (IIRC). Given the definitions of force &amp; torque as derivatives of momentum, this makes it seem much less certain that one should define either torque in terms of force or vice versa — it gives the impression they are more distinct than it first seemed.  That said, as far as I know a lot of physics is about defining &amp; describing “fundamental forces” — not “fundamental torques”.   So is choosing to use either force or torque as the basis of laws &amp; problems arbitrary? Or is there an actual fundamental rationale to when one or the other should be used?
66525
I did a weird activity and now I am trying to figure out the physics behind it:  While sitting on a chair I kept my feet above the ground and tried to move the chair forward. I was able to. Initially, I thought that perhaps the center of mass won't be changing as I was pushed backwards. But I moved the chair for a while and saw that it had moved a considerable distance and I was still sitting on the chair. Hence the center of mass did change for sure. According to Newton's second law, there must be an external force acting on the system(me and the chair). But I am not able to figure out what force is it. I have a feeling that it is somewhere related to the fact that the system is not completely isolated but I am not sure how.     Note: I am not in contact with the ground or any other object close to me. I have lifted my feet and have my hands on my lap.
4352
Given Newton's third law, why is there motion at all? Should not all forces even themselves out, so nothing moves at all? When I push a table using my finger, the table applies the same force onto my finger like my finger does on the table just with an opposing direction, nothing happens except that I feel the opposing force. But why can I push a box on a table by applying force ($F=ma$) on one side, obviously outbalancing the force the box has on my finger and at the same time outbalancing the friction the box has on the table? I obviously have the greater mass and acceleration as for example the matchbox on the table and thusly I can move it, but shouldn't the third law prevent that from even happening? Shouldn't the matchbox just accommodate to said force and applying the same force to me in opposing direction?
95059
The velocity of a vehicle while taking circular turn is tangential to circular path. Friction opposes relative motion between ground and tyres. Then how does friction act radially inwards?  In other words, why does the car tend to go radially outwards although its velocity is tangential?
104337
Take for example the case of a rod rotating about an axis passing through its centre of mass and perpendicular to it. It has a ring hung from one of its sides. The rotation of the rod causes the ring to move out wards and ultimately fall off the rod.   I asked my teacher what causes the ring to move out wards and he said the centrifugal force acting in the frame of reference of the ring causes motion. What exactly is the ring reference frame? Is it a rotating frame? How would u visualize motion in this frame of reference?
90872
Is there any true  in the universe?  Newton's first law states that an object at rest remains at rest, and an object performing uniform motion performs uniform motion, until and unless acted upon by an external force, if viewed from an inertial frame. It is the definition of an inertial frame of reference. And Newton's second law states that the net external force acting on a particle equals its mass times its acceleration. Thus we need to have an inertial frame in order for Newton's 1st and 2nd laws to be applicable.  Scientists claim that Earth is an inertial frame, either the  frame or the  frame.  Why is that? Earth's different parts have different accelerations when it performs rotational motion about its axis. Now you may say that Earth's axis is inertial, but the Earth is also revolving around the Sun. Thus Earth's frame should be non-inertial.  Even supposing that earth's frame is inertial, then it means that rest of the universe is non-inertial, because only a frame that moves with constant velocity with respect to an inertial frame is also an inertial frame and according to various scientific experiments there is no other matter in this universe which satisfies that criterion. Now you may say that earth is an approximate inertial frame, but still, my question is: is there any perfect inertial frame in the universe where Newton's laws are exactly applicable?