29
votes
Accepted
Why do we still use pseudo forces?
In practice, in newtonian mechanics, pseudoforces are used, because they're simple and convenient.
At the end of the day, they're only inertial terms that you're "disguising" as forces. You ...
- 5,594
12
votes
Why do we still use pseudo forces?
In an inertial frame $(t,x)$ Newton's law takes the familiar form
\begin{equation} F=m\frac{d^2 x}{dt^2}\;. \tag{1}\label{1}\end{equation}
Now write this in terms of a rotating coordinate frame $(t',x'...
- 477
9
votes
Correct explanation of tides
The tides (rise and fall of water in the sea) don't actually work like that. (A rare example of Isaac Newton getting it completely wrong.) It's more like the periodic forces act like the sloshing of ...
- 101
7
votes
Liquid pressure at the atomic level
First let me note that technically, even within your argument, the collision velocity could be higher or the collision frequency could be higher. Hence pressure in a gas is proportional to temperature ...
7
votes
Accepted
How does unbalanced force ever create?
Third law force pairs don't act on the same object. The third law states that if one object exerts a force on another, the second object exerts an equal and opposite force on the first. It doesn't ...
- 7,818
6
votes
Is weight distribution influenced by the location of the weight's attachment points (see drawing)?
Lets look at the equations
Static equilibrium
to obtain the unknows forces $~F_1~,F_2~$ you take the sum of the forces $~\sum F_i=0~$ and the sum of the torques about point A $~\sum_A\tau_i=0~$. you ...
- 10.5k
6
votes
Accepted
Addition of forces on a rigid body instead of a point
Extended objects, or in general any mass configuration, do obey Newton's second law. You don't have to assume you can treat the system just like a point mass, you can formally treat it as a collection ...
- 8,671
5
votes
Why do we still use pseudo forces?
In practice, you can't do without using pseudo forces a.k.a. "fictitious forces". The analysis of even quite simple classical mechanics problems can become extremely complicated if you don't ...
- 9,913
5
votes
Query in Newton's Third Law and friction
The force pushing the box and the force of friction are not a third law pair, there is no reason why they must always be equal and opposite. They may happen to be equal and opposite, as in the case of ...
- 7,818
5
votes
Accepted
Query in Newton's Third Law and friction
You gave a reasonably accurate description of static friction, but then you said it was kinetic friction. In kinetic friction, the magnitude of the force is constant and in the direction opposing the ...
5
votes
How does unbalanced force ever create?
...hence an equal and opposite force must be given to the person hence
the body must not move...What am I missing here ?
During free fall it is not the force of gravity that exerts a force on the air....
- 63.1k
4
votes
Accepted
Where do these forces come from?
The one-word answer is torque.
The door is not moving. That means that all forces must balance. So far so good. That is where the vertical forces on the hinges come from. The door has weight, which is ...
- 283
4
votes
Why do we still use pseudo forces?
The whole distinction between real and pseudo forces is a bit misunderstood. The forces that we call "pseudo" are effectively the forces that are explained by the current theory.
Gravity is ...
- 3,087
4
votes
Query in Newton's Third Law and friction
In addition, that friction and applied force is not a third Newton law force pair (because they acts on the same body),- friction responds to normal force, which usually is perpendicular to external ...
- 9,208
4
votes
Query in Newton's Third Law and friction
Newton's third doesn't say that these two forces should be on the same object. If you have two objects, $A$ and $B$, one of the two forces could on $A$ and the other on on $B$. The law can also be ...
4
votes
How does unbalanced force ever create?
This is a really common mistake people make when they first learn Newton's Third Law. I think it's partly because teachers often say the law badly.
Newton's Third Law says "if object A exerts a ...
- 6,409
3
votes
Angular Momentum vs. Force Due to Gravity
The force of gravity (let's say it's one object orbiting a much more massive object - the sun) is an inward pointing force. That's why angular momentum is conserved - because the force is always ...
3
votes
Addition of forces on a rigid body instead of a point
We can perform the vector sum of external forces to get net external force $\overrightarrow F_{ext}$ on any object not just a point mass or a rigid body but any collection particles interacting or ...
- 177
3
votes
Accepted
Question in time period of oscillation of a ball in bowl
The bob is an essential part of the pendulum, so people include the length of the bob as a natural part of the length of the whole pendulum. On the other hand, a ball and a bowl aren't usually thought ...
- 23.3k
3
votes
Query in Newton's Third Law and friction
You need to distinguish between kinetic friction and static friction. It is static friction the prevents the object from moving at all. Static friction is a variable force that matches the applied ...
- 63.1k
3
votes
Accepted
Confusion regarding net acceleration of the bob in the bottommost point of the trajectory of a pendulum?
Consider a mass going around a circle of radius $r$ at constant speed $v$. Since we know how it moves, we can calculate the acceleration of this mass (the rate of change of velocity), irrespective of ...
- 8,671
3
votes
How does unbalanced force ever create?
If A exerts a force on B, B exerts an equal and opposite force on A. Both A and B are accelerated.
In this case, a falling skydiver pushes air out of the way, accelerating the air downward. The air ...
- 31.1k
2
votes
Tangential Acceleration of a pendulum
The swing angle obeys the following dynamics
$$\ddot{\theta} = -\tfrac{g}{\ell} \sin \theta $$
and the tangential acceleration component is
$$ \ell \ddot{\theta} = -g\,\sin \theta $$
Using the small ...
- 35.8k
2
votes
Is weight distribution influenced by the location of the weight's attachment points (see drawing)?
The line of action of the force of gravity on the 100 kg weight in the first diagram acts through the same point on the structure as the physical connection of the vertical support of the weight in ...
- 63.1k
2
votes
Calculating momentum change?
Momentum is a vector, so actually its change, being a vector sum, is itself a vector. Asking "what's the change in momentum" is a little misleading. If they asked you "what changes in ...
- 289
2
votes
Angular Momentum vs. Force Due to Gravity
In the case of orbital bodies, energy and angular momentum are conserved.
Maybe it is useful to compare with a situation where only energy is conserved: a simple pendulum. The speed increases as the ...
- 13.7k
2
votes
Angular Momentum vs. Force Due to Gravity
If a force $\vec F = \hat n F(r)$ than $\vec F$ is a central force, where $\hat n$ is the unit radial vector in spherical coordinates. $\vec F$ is only in the radial direction and only depends on the ...
- 8,957
2
votes
Why do we still use pseudo forces?
I don't I think if it's anti physics to use pseudo forces as they are quite incredibly significant in non inertial frames to convert the motion into inertial frame. And using pseudo forces gives an ...
- 17
2
votes
Why do we still use pseudo forces?
Pseudo forces are a tool, which can be useful in certain situations. Sometimes it is simpler to work in a non-inertial frame and so introduce pseudo forces; sometimes not.
The key thing to remember is ...
- 40.9k
2
votes
Accepted
Coriolis force on a person on a carousel
There is centripedal force in the rotating reference frame. Your explanation for the nonrotating reference frame was right. The accepted answer of that question says there is a net inward force of $m\...
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