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 ...

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2answers
70 views

Can you launch an item farther by slamming into it or accelerating it along a length

I am trying to desgin a little penny balista toy (built with a 3d printer). The short description is that there is a track with a mass ("hammer") that slides along it. There is a stack of pennies in ...
0
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3answers
356 views

How to imagine the following power and torque?

I can roughly feel a force of 10 newton only by considering the weight of 1 kilogram object. How to imagine the following measurements? Maximum horsepower 16 hp @ 9,500 RPM Maximum torque ...
2
votes
5answers
521 views

Find drag force on link of rotating chain

Given a closed chain with a total length of 1.2m rotating at 1'800 rpm and a total mass of 0.4kg, what is the drag force pulling on one chain link? I originally thought that since no link size was ...
4
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3answers
1k views

Why do we need the quantity momentum?

Why do we need the quantity Momentum in physics when we have the quantities like Force and Energy? Isn't it possible to substitute the usage of Momentum with equivalent of Force and Energy?
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1answer
108 views

In hydrostatics, is it possible for the bouancy to be greater than the weight of a body?

In the diagram we have two bodies, with density and volume $\delta$ and $V$, and a fluid $\ell$. $$\delta_1=0,7 \rm\frac{gr}{cm^3}$$ $$\delta_2=2 \rm\frac{gr}{cm^3}$$ $$V_1=100 \rm {cm^3}$$ $$V_2=10 ...
2
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2answers
982 views

Calculating forces in a mass suspended by four cables

As a project, I am designing a cable-controlled camera system (i.e., a home-made Skycam clone). Basically, it is a mass suspended by four cables connected to fixed points; by lengthening or shortening ...
1
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1answer
2k views

Two problems with free body diagrams. Contradictions (solutions are provided)

This problem is similar, but also different question from my previous question. They are both unfortunately long. Problem/Solution #1 ! ! Quick Concept Check a) Could someone briefly explain to me ...
8
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0answers
381 views

Measurement of Tangential Momentum Accomodation?

(this question is a crosspost from theoretical physics.) I am using atomic force microscopy (AFM) for characterizing pores of the size of nanometers for application in gas flow. For this, knowing ...
2
votes
1answer
748 views

Circular Motion Equation Derivation

I am given a series of three equations, which someone has used to determine the Tension force in a rope swing: $$mgh=1/2mv^2$$ $$T-mg=\frac{mv^2}{r}$$ $$T=3mg=1764N$$ I am asked to exaplain the steps ...
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2answers
916 views

How to get statics out of a dynamic force concept?

If one defines force as the time derivative of momentum, i.e. by $$ \vec{F}= \frac{d}{dt} \vec{p} $$ how can this include static forces? Is there a generally accepted way to argue in detail how ...
2
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1answer
614 views

Combined Gravitational Force Vectors in a Spherical Coordinate System

Asking a question here is quite intimidating for me -- while I love Physics, my high-school understanding only allows me to go so far... I've been trying to solve this problem for the last couple of ...
1
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0answers
165 views

Hooke's Law and the shape of coils

I've learned in school that the force in a coil is $F=kx$, linear on how much the coil is stretched. Two questions: Is it always linear for every shape of a coil? Does it remain linear if we ...
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1answer
1k views

How positively charged protons remain glued to each other while they should repel each other out of nucleus? [duplicate]

Possible Duplicate: Protons' repulsion within a nucleus How positively charged protons remain glued to each other while they should repel each other out of nucleus?
1
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0answers
321 views

Slackline Jump Tension

So a slackline is basically a bouncy tight rope. I found a site that has a calculator for the tension of a static slackline ...
1
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1answer
696 views

What forces act on a person sitting in a chair with wheels when they push off another stationary object

What is slowing me down when I push off my desk? What are the "Major" contributors? and Does how hard I push with one hand (or with two hands) make a significant difference?
0
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1answer
148 views

Say we're driving a bike and suddenly hold the brakes?

It's easy for me to imagine that if we brake the front wheel then there is a chance that I'll flip. On the other hand if I brake the back wheel, there is no way it'll happen no matter how fast I ...
12
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4answers
1k views

How to sail downwind faster than the wind?

Recently a group set a record for sailing a wind-powered land vehicle directly down wind, and a speed faster than wind speed. Wikipedia has a page talking about it, but it doesn't explain exactly how ...
1
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2answers
157 views

Please explain this circular movement problem [closed]

I was working over some problems from my physics textbook, and I came across this one, it involves circular movement: A car with the mass of 1t is moving over a hill with the velocity of 20 m/s. The ...
1
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1answer
422 views

What conditions must be met for a ball to roll perfectly down an incline without slipping?

What conditions must be met for a ball to roll perfectly down an incline without slipping? A mathematically rigorous definition, please. I honestly don't know where to begin with answering this ...
2
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1answer
218 views

Does a slinky hanging downward double in length if gravity doubles?

Also would a spring under tension greater than the force of gravity pulling the spring downward shrink in both directions until it has depleted it's stored energy while in free fall?
4
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2answers
412 views

Why don't massive water-borne animals crush under their own weight when they're in water?

If you take a giant whale out of the water and put it on land for long enough, it will crush itself under its own weight. Why doesn't the animal get crushed under its own weight when it's in water?
1
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1answer
687 views

Trajectories using Polar Coordinates

Once I asked my teacher how to find the trajectory of any particle that is acted upon any force.(Generally) He Told me that I couldn't do it as I did not know polar coordinate geometry as of then but ...
2
votes
1answer
129 views

How should I be thinking about tides?

I am working on a project for physics that involves tides. This is my current mind set when thinking about tides: The earth applies a gravitational force on some mass ...
2
votes
2answers
243 views

Interaction speed between electric charges and magnetic materials

Einstein said that the speed of a matter in universe cannot exceed the speed of light. Is it correct for electric force transmission speed from one electric charge to other one? What is ...
2
votes
1answer
583 views

Conservation of Energy in Special Relativity

In classical Newtonian mechanics, from what I understand, conservation of energy stems from the fact that all known forces are conservative forces, and vector calculus tells us that they can be ...
0
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1answer
296 views

Does friction act in the same way in different directions?

A physics textbook is launched up a rough incline with a kinetic energy of $X$ joules. When the book comes momentarily to rest near the top of the incline, it has only gained ($X-20$) joules of ...
1
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1answer
939 views

Force in relation to stationary and non stationary objects

Say you have two situations with an object interacting with the ground. In the first situation the object has been sitting on the ground for a while so the force will be mg. In the second situation ...
8
votes
5answers
9k views

Why does work equal force times distance?

My 'government-issued' book literally says: Energy is the capacity to do work and work is the product of net force and the 1-dimensional distance it made a body travel while constantly affecting ...
1
vote
1answer
103 views

More efficient far-future means of keeping the earth alive? [closed]

In about 7 Billion years our planed will be consumed by the ever-growing sun, life would have become extinct long before that. That means that in several hundred thousand years we have a deadline to ...
1
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0answers
212 views

Simple: What do these ballistic impact numbers represent?

I bought physics for game programmers, found here, today to study ballistic impact, but I'm confused as to where a few numbers are coming from. I'm basically looking to understand what the values ...
0
votes
1answer
269 views

Momentum question?

The problem: In a car crash, a passenger with a mass of 82kg is not wearing a seatbelt. The car is travelling at 45km per hour. What impulse must the car's airbag provide in order to stop the ...
0
votes
2answers
1k views

How to interpret this vertical circular motion problem?

A bucket of water is tied to a rope and swung in a vertical circle. The distance from the bucket centre to the axis of rotation is $2.08m$. Calculate the angular velocity (in $rad s^{-1}$) of ...
1
vote
1answer
445 views

What techniques can be used to analyze a rod rotating about the edge of a table?

A uniform rod of length $4x$ is rotating about the edge $O$ of the table. (The rod does not fall off the table.) The centre of mass $G$ of the rod is distance $x$ away from $O$. The rod is making ...
0
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1answer
455 views

Value and direction of the force applied by a rubberband on an object

Is there a model that would allow me to compute the value and the direction of the force F applied to the object in this case: I have to fixed points: $ A = (-l/2,0) $ and $B=(l/2,0)$. A rubberband of ...
4
votes
3answers
3k views

How does gravity force get transmitted?

How does gravity force get transmitted? It is not transmitted by particles I guess. Because if it was, then its propagation speed would be limited by the speed of light. If it is not transmitted by ...
2
votes
1answer
981 views

Normal force in a compound pendulum (physical pundulum) system?

Consider a compound pendulum pivoted about a fixed horizontal axis, illustrated by the force diagram on the right: # Okay, I can't figure out where the normal force on the pendlum should point ...
2
votes
2answers
479 views

What sustains a rigid body's rotation at its constant angular(rotational) speed?

Continuing from the following scenario from my previous question Centripetal force of a rotating rigid body? : Consider someone pushing a roundabout in a playground. Initially the roundabout is ...
6
votes
3answers
994 views

How does $F = \frac{ \Delta (mv)}{ \Delta t}$ equal $( m \frac { \Delta v}{ \Delta t} ) + ( v \frac { \Delta m}{ \Delta t} )$?

That's how it's framed in my Physics school-book. The question (or rather, the explanation) is that of the thrust of rockets and how the impulse is equal (with opposite signs) on the thrust-gases and ...
1
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3answers
2k views

Centripetal force of a rotating rigid body?

Consider someone pushing a roundabout in a playground. Initially the roundabout is stationary, but when it is pushed, it rotates with increasing rotational speed. The force of the push is ...
2
votes
3answers
2k views

Why did they add a Centripetal Force in the Free-Body Diagram?

problem ! solution ! Why do they have the centripetal force in there? I understand that the normal force is the centripetal force here, but why would they say "or $\frac{mv^2}{r}$"? I thought it ...
-1
votes
4answers
905 views

A person weighing 100 N stands on some bathroom scales in a lift. If the scales show a reading of 110 N, which way is he going [closed]

Can someone answer and explain it please. Here are the options: Moving downwards and decelerating. Moving downwards with a constant velocity. Moving upwards and decelerating. Moving upwards with a ...
0
votes
2answers
2k views

Would this model of a boat move according to Newtons 3rd Law?

If i have a small toy boat with a sail, and i attach a fan onto it, FACING THE SAIL, which runs by solar. Once the fan turns on will the boat move or will it remain at rest. Apparently it wont because ...
3
votes
2answers
363 views

Does constraint for speed of Electric and magnetic fields violates Conservation of momentum or Newton's third law?

I'm just a beginner so bear with me. Consider two frames at rest wrt to each other separated by distance enough for light to take a minute or so. At a given instant we create two large dipoles by some ...
3
votes
3answers
3k views

Deadlifting the rear end of a car with a lever. What it equates to in actual weight?

Consider this youtube video of a guy lifting a car. (skip to 2:15). I checked, and these cars (PT Cruiser) weigh $1417\:\rm{kg}$. What would the equation be to estimate how much weight he is actually ...
4
votes
1answer
554 views

A Question about Virtual Work related to Newton's Third Law

In describing D'Alembert's principle, the lecture note I was provided with states that the total force $\mathbb F_l$ acting on a particle can be taken as, $$\mathbb F_l=F_l+\sum_mf_{ml}+C_l,$$ ...
1
vote
2answers
958 views

At what point does a projectile leave a slingshot?

Assuming a frictionless / "perfect" environment, and given a ball held in an elastic sling (like a hand-held catapult) where the pocket is lighter than the projectile itself, what is the point at ...
1
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0answers
223 views

Modeling the trajectory of a particle in an Electric field [closed]

[This problem has been resolved, sorry for posting in the wrong forum!] (I was trying to model the trajectory of a particle in an electric field.)
13
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4answers
1k views

Helicopter in an Elevator

You buy one of those remote control toy helicopters. You bring it into an elevator. The elevator goes up. Does the helicopter hit the floor or does the floor of the elevator push the air up into the ...
0
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2answers
4k views

Jumping in an elevator?

I've always been under the impression that jumping in an elevator wouldn't help at all, especially after reading a snippet of physics where Einstein said that free fall was identical to zero gravity. ...
8
votes
3answers
443 views

Whether $m$ in $E=mc^{2}$ and $F=ma$ are both relativistic mass?

I know that $m$ in $E=mc^{2}$ is the relativistic mass, but can $m$ in $F=ma$ can also be relativistic? If the answer is yes, then can you tell me whether this equation is valid $E=\frac{F}{a}c^{2}$? ...