This tag is for the classical concept of forces, i.e. the quantities causing an acceleration of a body. It expands to the strong/electroweak force only insofar as they act comparable to ‘classical’ forces. Use [tag:particle-physics] for decay channels due to forces and [tag:newtonian-mechanics] or ...

learn more… | top users | synonyms (1)

1
vote
1answer
65 views

Why can center of mass be used in calculating gravity?

Why can gravitational forces be based on the center of mass. Due to the fact that gravity is related to the square of the distance should not the gravitational sum of every particle exceed the force ...
-1
votes
1answer
39 views

Centripetal Force [closed]

What is the size of the force required to cause a car of mass $1.75\times10^3$ kg to travel in constant circle of diameter $25.0\space m$ with a constant speed of $25.0 \space ms^{-1}$ ?
1
vote
0answers
27 views

What is the impact force of my punch while running at 28.8 km/h [closed]

My weight is 73 kg, my height is 1.87 m, my running speed is 28 km/h, and the speed of my punch is 61 km/h. the person i punched weighs 61 kg, and is 1.67 m tall. with how much force did i punch a ...
1
vote
2answers
55 views

What depth should water be filled to in a cylinder flask to make it the most stable

As said in title, a cylinder flask with a mass of 100g and radius of 3 has a center of balence 10cm above the base. Assuming negligible wall thickness, to what depth should water be added to this ...
1
vote
1answer
59 views

What constitutes a force? [duplicate]

There are a few questions on here about why Gravity is not a force, but I'm having trouble grasping why exactly. It sounds to me that Gravity is not a force because it is simply a by-product of mass ...
2
votes
4answers
554 views

Is Newton's second law tautologous? [duplicate]

Newton's second law $$\mathbf{F} = m\mathbf{a}$$ where $\mathbf{F}$ is the force, $m$ the mass, and $\mathbf{a}$ the acceleration, seems at first blush to be a simple tautology, since $\mathbf{F}$ ...
1
vote
1answer
40 views

Stacking compasses and what happens

A fellow science teacher had his compasses stacked on top of each other. He is teaching orienteering to his MO Science class. He noticed that they moved away from North and that each one would ...
0
votes
3answers
126 views

Sliding and rolling friction

I heard that friction depends only on the normal force but not on the contact area. Let's take a cube and a sphere which are of same weight (then normal force will also same ) but the force needed to ...
79
votes
10answers
13k views

If gravity isn't a force, then why do we learn in school that it is?

I have studied some of Einstein's Theory of General Relativity, and I understand that it states that gravity isn't a force but rather the effects of objects curving space-time. If this is true, then ...
0
votes
1answer
36 views

Calculating constant velocity from friction [closed]

I'm unsure if my Book is wrong. Either way, we send a pinball through a cylinder filled with oil, the forces that apply are. Fpinball = 15,8 ∙ 10^−6 ∙ 9,82 = 5,69 ∙ 10^−5N Foil = 𝜌 ∙ 𝑔 ∙ 𝑉 = ...
8
votes
2answers
336 views

A false proof of drag force being conservative

Consider a particle moving along some trajectory in the $x$-$y$ plane, in a viscous medium. Then its equation of motion is given by: $$\mathbf{F}_d = - b \mathbf{v} .$$ it's well-known from the ...
1
vote
0answers
48 views

Water level in rotating glass [closed]

I have a glas with water in a train and the train is driving a curve (v and R given). How does the level of the water change? I know that I have the gravity and centripetal force, but how do I ...
2
votes
1answer
99 views

How does hydraulic press work at molecular level?

Let's consider the following arrangement: I know that because of conservation of energy the force on the car has to be amplified. The work $W$ done is $$W = \text{Force} \cdot \text{distance} \, ...
0
votes
2answers
86 views

How does a cyclist moves the center of mass of the cycle-cyclist system?

Consider the image shown below, In the left diagram the centre of mass of the system lies upon the perpendicular from the point of contact. But in the right diagram the centre of mass has shifted ...
0
votes
1answer
35 views

How can I work out tensions using moments? [closed]

If you were given the weight of a metre rule, its weight and the distance between 2 vertical rods holding it up, how would you work out the tension in the rods using the concept of moments or vectors? ...
1
vote
2answers
60 views

Which has the larger change in momentum [closed]

This is a concept question in my physics class, It isn't for marks, its just to gauge your understanding of the subject. I'm not sure if I have the right idea. since the mass of block A is 4 times ...
3
votes
2answers
278 views

Max extension of spring mass system

While attempting problems of simple harmonic motion I came across this problem, which has gotten me confused. A fixed horizontal spring is stretched by a constant force $F$. I am required to obtain ...
3
votes
3answers
63 views

How to model vibration damped by applied/contact force?

I am computer science student and I am working on a project which needs to know how the vibration of phone is damped by applied force (when human touches the phone). I have read many articles about ...
1
vote
1answer
20 views

Transferable force

If I for example have two rectangular pieces of steel that are both W=40mm, L=1000mm, H= 40mm and are both completely ridged. One piece of steel is resting on top of the other piece of steel, if I ...
1
vote
0answers
28 views

work done in observer frame

I had a few questions. 1) Is work done independent of the refrance frame? 2) Suppose a cart-A with rough surface is accelerating with an acceleration a and another cart-B with acceleration b. Now to ...
0
votes
2answers
48 views

Resolving resultant force into the components

I hate to use this medium in the wrong way, and I understand the fundamental principles to this question. However, The question goes that you must resolve the resultant force (R=500N) into its ...
0
votes
4answers
56 views

Must one include friction and gravitational force in the work term?

Example problem: "A sled has an initial velocity up a ramp of 5 m/s, the ramp has an angle of 20 degrees to the horizontal, and the coefficient of dynamic friction between the sled and the plane ...
0
votes
0answers
27 views

Force exerted by pulley on ceiling

I read in my book that when a pulley is accelerating it exerts more force on the ceiling than when it is still. I know the derivation and I can mathematically prove it but I'm unable to get my head ...
1
vote
1answer
30 views

Relation of Force and Energy, from a biophysics point of view

Considering us humans practically, does energy require force, ie we do apply some internal and external forces to do work, or does force require energy. ie we can only apply a force on an object if we ...
0
votes
0answers
25 views

How rotational force calculation depends on the distance between the point of force application and the axis of rotation?

I don't understand how the perpendicular distance between the point of force and the axis of rotation gets involved in the calculation of the rotational effect of that force.Is it about rotational ...
1
vote
1answer
49 views

Is there a principal difference in acceleration from an impulse and the free fall of a body in the orbit around a gravitational mass?

Especially taking in account that acceleration need a force which leads to some conversion of energy. This is not the case for orbital motion, such a acceleration does not convert energy. That seems ...
0
votes
1answer
50 views

How do forces affect work? [closed]

I was doing my homework and I came across the question: Suppose that two objects, each with the same mass, are accelerated from rest to the same velocity. The force that accelerates one object ...
-2
votes
3answers
103 views

Disregarding the claim of perpetual motion. Does this design have any merit at all?

I'm wondering, in reference to this youtube video Whether or not this design would actually make the wheel move. Any big brains out there wanting to help me out would be greatly appreciated
0
votes
1answer
49 views

Please help me with this doubt from center of mass concept

Take the case of Atwood machine where masses of blocks are $m$ and $2m$. The acceleration of individual masses are $\frac g3$. now the acceleration of center of mass of masses and string system is ...
1
vote
0answers
54 views

How to push a ball out of tube without air compression or springs [closed]

For my physics class, we have to make something that can shoot a ping-pong ball up to 7 meters and is very accurate. My group didn't want to use the traditional catapult design. Instead, we want to ...
0
votes
2answers
43 views

Can upward resistive force be greater than downward gravitational force?

Objects falls through air, eventually it will reach terminal velocity, but why won't this upward force increase further?
1
vote
3answers
76 views

Why do objects move when you apply a force that's equal in magnitude to the friction? [duplicate]

If the friction on an object is 200 N and you apply 200 N, it seems, the forces should immediately cancel each other out since the friction and your applied force go in opposite directions, leaving ...
2
votes
1answer
59 views

Why is friction not dissipative in rolling motion? [duplicate]

We know that non-conservative forces like friction is a dissipative force. But according to my book when a solid cylinder is rolling down a rough inclined plane of inclination angle $\theta$ the ...
0
votes
0answers
42 views

Problem in constraint equations

In this, if I want the acceleration constraint between $M$ and $2M$, I write $AM+2AB$=LENGTH OF STRING, which on differentiating twice gives $a_{m}=2a_{2m}$(which turns out to be correct). However, ...
1
vote
3answers
91 views

Acceleration - Constant force vs force for an instant

I am reading about Newton's second law, and I am slightly confused. So I think I get that $F=ma$ can be used to find acceleration. I am struggling between two scenarios: constant force acting over a ...
0
votes
2answers
58 views

Equilibrium equations

You have one horizontal beam. Its left point is attached to a free pivot at the vertical wall. Its right point is suspended by a rope from the ceiling. Nothing is moved. So $\sum F=0$ and $\sum M=0$. ...
0
votes
1answer
48 views

how to test whether a potential gives rise to a force field

A preamble to my problem. I have measured a discrete vector field, $\vec{F}(x,y) = (F_x(x,y), F_y(x,y))$ representing some forces i'm currently researching. $\vec{F}$ is the average of forces acting ...
1
vote
0answers
19 views

Gyroscopic precession force translated 90 degrees? [duplicate]

I was watching a video on propeller gyroscopic effect, please take a look at this 1 minute segment (up to 6:06): https://youtu.be/QGWbjGqmoWo?t=307 Alternatively, here is a summarizing image from ...
7
votes
1answer
114 views

How strong must a tornado be to pick up a shark?

Yes, you know where this is going. There is a good article on this topic by National Geographic: 'Sharknado' Got One Thing Right: Aquatic Animals Sometimes Do Fall From the Sky One of the first ...
1
vote
0answers
68 views

Compute the gravitational force between two vertical rods [closed]

My AP physics teacher posed this problem at the end of his lecture today and I want to be sure my physical set up is correct (I've already done the math, but just double checking!). The situation is ...
0
votes
1answer
58 views

Potential Energy [closed]

I really need help with this homework question. I thought the function very stranger to be a function of a potential energy. It´s seems to be like Lennard Jonnes pontential energy function. Am I ...
0
votes
2answers
52 views

Using gravity's force to do work?

Since gravity is everywhere and we don't need to do anything to feel it and interact with gravity, can we somehow extract the gravity force to do work and power machines? For example, we've nuclear ...
2
votes
1answer
51 views

Does third law of motion apply to light or EM waves? [duplicate]

Third law of motion - "For every action there is an equal and opposite reaction" I was considering the situation, where I may be motionless in space with only a flashlight and no forces acting on me. ...
0
votes
3answers
171 views

Why is walking up stairs harder than walking normally?

I must admit, I'm pretty new to studying physics and I know this is a simple concept but I'm having difficulty understanding it. I've tried reading the questions here but I just need a little bit of ...
1
vote
0answers
20 views

Gravitational cut [closed]

When does the gravitational force cuts off when the plane pull off? I tried to measure the gravity of the plane when is on the ground and when it start to pull off my question does gravity cuts at 39 ...
0
votes
3answers
65 views

Does the work done by a person equal the work done on the object in this situation?

If you applied a constant force over a floor that has friction on an object, would the work done by the person equal to the work done on the object? Assume that the floor is flat and that the object ...
0
votes
0answers
55 views

Circular Motion: Rubber Stopper Lab

During a lab I was doing involving uniform circular motion, we had to spin a rubber stopper horizontally via a rope. At the bottom of the rope, there was some weights. I have to answer this question ...
23
votes
4answers
5k views

Why doesn't a spinning object in the air fall?

Let's say I have a ball attached to a string and I'm spinning it above my head. If it's going fast enough, it doesn't fall. I know there's centripetal acceleration that's causing the ball to stay in a ...
1
vote
2answers
41 views

Does air resistance give a falling skydiver weight?

An observer in free fall is weightless as he is accelerating at 9.8 m/s^2. However, when a skydiver jumps from a high plane, his acceleration gradually slows until becoming 0 m/s^2 at terminal ...
0
votes
1answer
59 views

Properly deriving the formula for the kinetic energy

I am a physics student and recently attended my first lectures. One thing that strikes me even now was the way the professor derived the formula for the kinetic energy. He started with the (already ...