Questions tagged [free-body-diagram]

A pictorial device which analyzes forces present on any body with the use of vectors. Allows easier grasping of problems involving either objects at equilibrium or in motion. Can be used to predict presence of forces.

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160
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20answers
136k views

Given Newton's third law, why are things capable of moving?

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 ...
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10answers
18k views

Why I think tension should be twice the force in a tug of war

I'm going to provide my argument for why I think the tension in a rope should be twice the force exerted on either side of it. First, let's consider a different example. Say, there is a person named <...
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3answers
13k views

When is tension constant in a rope?

Consider a massless rope with pulling forces applied at each end. How do we decide if tension is constant or not in a rope? Consider a few example scenarios: For example, if there is a knot in the ...
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3answers
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Can you lift a basket up while standing inside it? [closed]

Suppose you stand in a basket and you try to pull the handles of the basket. Will you be able to lift the basket from ground? Similarly, Baron Münchhausen allegedly pulled himself and the horse on ...
3
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2answers
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Rolling resistance and static friction

I am a bit confused about the relation between rolling resistance and static friction. I have often heard that it is the static friction that lets the wheel roll. Consider the following two cases: ...
49
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3answers
19k views

If Newton's third law is true, why can we sink in sand? [duplicate]

Newton's third law of motion states that every action has an equal and opposite reaction. That is the reason we do not sink into the earth, because when our weight exerts a force on the earth it also ...
7
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3answers
4k views

Tension in an Atwoods machine conceptual?

Assuming $T_1$ is the force that acts on box $1$ and $T_2$ is the force that acts on box $2$. Exactly what causes the Tension? Why does $T_1 = T_2$? The problem is we are told to memorize that $T_1 =...
11
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3answers
31k views

The direction of frictional force in smooth rolling motion

I want to ask about the direction of frictional force in smooth rolling motion which means the rolling object doesn't slide on the surface. Here is the first case, the wheel rolls to the right so the ...
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4answers
4k views

Can momentum be conserved in a perfectly elastic collision?

I am taking for granted that when we say that something is conserved it is understood 'in its full integrity'. Energy is represented by a scalar J, and is conserved in elastic collision. momentum ...
22
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6answers
5k views

Would you feel Centrifugal Force without Friction?

This question arose from my sci-fi discussions with my friend. It concerns artificial gravity through centrifugal Force. Partly inspired by the Artificial Gravity created on the Hermes ship from the ...
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6answers
5k views

Why does a car engine not do work if the wheels don't slip?

I saw this mind boggling result that if the tires don't slip then the work done by an engine to move a car is zero. Why is this true? Moreover, what does this truly mean? Update: Sorry about not ...
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7answers
27k views

Is gravity a force and if so what is its opposite?

For every force there is an equal force in the opposite direction on another body, correct? So when the Suns gravity acts on Earth where is the opposite and equal force? I also have the same ...
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3answers
891 views

Watching something fall into a black hole from far away

I am observing (theoretically) an object falling into a black hole from a safe distance away. My understanding is that from far away it appears as if the body will asymptotically approach the event ...
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3answers
2k views

If $F=ma$, how can we experience both gravity and a normal force even though we are not accelerating?

As I sit in my chair, I experience a gravitational force pushing me into the chair and I'm also experiencing the normal force of the chair pushing back at me so I don't fall. According to Newton's ...
3
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1answer
1k views

Why is tension in a rope the same at every point?

So, I had this lecture where it was explained that if the pulley is friction-less, then the tension on any point of the rope is going to be same. I can understand the friction-less part, as pulley is ...
5
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2answers
2k views

Rigorously proving equal tension on both ends

There is always one point in introductory mechanics that has been continuously bothering me ever since I had taken my freshman physics course - Why does a massless rope have its tension equal on both ...
15
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5answers
5k views

How do levers amplify forces?

This is really bothering me for a long time, because the math is easy to do, but it's still unintuitive for me. I understand the "law of the lever" and I can do the math and use the torques, or ...
18
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6answers
8k views

Why doesn't Newton's third law mean a person bounces back to where they started when they hit the ground?

When we drop a ball, it bounces back to the spot where we dropped it, due to the reaction forces exerted on it by the ground. However, if a person falls down (say, if we push them), why don't they ...
7
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3answers
18k views

Which force makes a wheel roll down the hill? What causes friction?

A wheel rolling down a hill has two axis of rotation. One is where the center or mass is and the other is the point of contact with the surface which acts as a fulcrum. I was trying to understand how ...
5
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3answers
1k views

The direction of static friction?

In my book, the following are described to be the steps that one must follow if he wishes to find the direction of static friction force acting on an object: "(1) Draw the F.B.D(free body ...
3
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3answers
117 views

How to understand the ambiguity of vector resolvation?

When we solve problems where there is a pendulum suspended using a tight, inextensible string and the question asks about the tension developed in the string at the highest point of the bob's swing. ...
3
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2answers
929 views

Question about normal force acting on a mass on an inclined plane

Suppose we are given the free-body diagram above, with a mass on an incline at an angle $\theta$. If my coordinate axes are taken to be the regular $x-y$ plane rotated an angle of $\theta$ (i.e. the x ...
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1answer
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When do we assume that a rope has different tensions in different places?

Working a problem with 2 pulleys and masses in class this week the professor at one point assumed that the tension on the two sides of a pulley would be different. Every other time we've done a ...
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1answer
3k views

How is circular motion possible on a banked road when there is no Friction?

It is given here that the maximum safe speed of a vehicle on a banked road having coefficient of friction $0$, is $V =\sqrt{R g \tan \theta}$, where $\theta$ is the angle of banking. I can't ...
51
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8answers
14k views

How does tilting a bike make it turn sharper?

Note that my question is not why do you tilt your bike when on a curve. It's about the reduction in turning radius when one tilts the bike inwards. Short to-the-point answers are welcome.
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14answers
38k views

Is Newton's third law always correct?

Newton's third law states that every force has an equal and opposite reaction. But this doesn't seem like the case in the following scenario: For example, a person punches a wall and the wall breaks. ...
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5answers
31k views

Why can't a rope be pulled completely straight?

I have found several discussions on how to calculate the sag of rope that is tied off at two points (like a tightrope), and I understand it to a certain extent. What I can't wrap my head around is how ...
18
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5answers
4k views

If Newton's third law is true, why do things compress?

According to the third law of Newton, every action has an equal and opposite reaction. This would (to me) suggest that every surface should put a force exactly opposite the weight of the body. If so, ...
11
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6answers
3k views

Why doesn't friction accelerate a ball undergoing rolling?

Consider this situation: A ball is moving forward and undergoing rotation. Assume that it is not slipping. Eventually, the velocity and rate of rotation of the ball decrease, and it comes to a halt. ...
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4answers
10k views

Particle sliding on a sphere

I believe most of you probably solved the following problem using energy conservation as shown here. It states A particle starts from rest at the top of a frictionless sphere of radius R and ...
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2answers
4k views

Massless string Paradox

If we introduce the notion of a massless string to denote the fact that net force on a massless string will always be $0$, since it is massless. How can these massless strings ever accelerate when ...
7
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3answers
35k views

Why are tensions in the pulley different when the pulley has a mass or moment of inertia?

When two blocks are connected by a string passing over a pulley whose moment of inertia is given (means pulley is not massless) then why does the string not have same tensions? What will be the ...
6
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3answers
25k views

Tension of rope. Different Answers?

The tension of a rope in a tug of war with unequal forces is equal to the least force on the rope. Am I right? (If group A pulls the wire with 20 newton leftwards and the group B pulls with 30 newton. ...
6
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6answers
1k views

Why does the friction act on the inward direction when a car makes a turn on a level road?

I tried looking this question up online but am left a little confused with all the answers, and the diagrams. When a tire of a car negotiates a turn in the road, there exists friction which is ...
5
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2answers
1k views

Can a massless rope accelerate?

Suppose I have an Atwood machine, that is, two different masses connected with an inextensible, massless rope over a pulley. Assuming no friction between the rope and the pulley, the heavier mass will ...
4
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3answers
275 views

Why is velocity of the mass $v/ \cos θ $? Why not $2v \cos θ$?

If we call the velocity of the mass $u$, then we can say: $u \cos θ = v$ and hence $u= \frac v{\cos θ}$. But why can't we write $v \cos θ= u$ and add the contribution from both of the strings: $u= \...
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1answer
3k views

Tension on a massless string

Is it possible to prove that a massless string has the same tension throughout, through contradiction? I've looked through several proofs online, such as Consider a massless string being pulled ...
13
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3answers
2k views

How does the center of gravity work?

In free body diagrams, such as a beam attached horizontally to a wall, $F_g$ is always shown acting on the center of gravity of an object. My question - is this the case in real life, where gravity ...
4
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3answers
5k views

Conical vs Simple Pendulum

I don't understand why the Tension $T$ on a conical pendulum and a simple pendulum are different. In a simple pendulum, one would say that the tension of the rope is $T=mg \cos(\theta)$. simple ...
3
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1answer
303 views

Reaction forces in pyramid stacking of steel coils

I was tasked with solving this problem at work as we are out of coil holders and we bought 140 coils and need to stack them asap. Companies that make the storage holders are on back order for several ...
2
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5answers
125 views

Free body diagram on a rack of wooden blocks [closed]

Considering a rack of blocks, and that I am able to hold it up in a horizontal line without it collapsing. I am trying to draw the free body diagram of one of the blocks in the middle portion, block A....
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2answers
490 views

Newton's third law (action and reaction) and work done with a wheel

I'm aware of the common misunderstanding about action and reaction canceling each other; they don't because they don't act on the same object. This is about a more subtle issue: exactly where is the ...
0
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1answer
6k views

Force of friction in rolling without slipping

Observe this case. We can make two choices regarding the axis of rotation. If we choose an axis of rotation that passes through the center of mass $G$ then the only force that would cause the ball to ...
3
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4answers
36k views

Normal force on vertical circular motion

I have a couple of questions concerning vertical circular motion. The object shown in the diagram moves with constant speed on the inside of a circle. In point A the normal force points to the center ...
2
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3answers
2k views

Friction when walking

To meet a U.S. Postal Service requirement, employees’ footwear must have a coefficient of static friction of 0.5 or more on a specified tile surface. A typical athletic shoe has a coefficient of ...
2
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4answers
591 views

Newton's second law explanation

I remember the first time I saw this formula, $F = ma$, and it seemed perfectly correct and natural to me (in the sense that it is very straight-forward and logical, not that it is easy by any means). ...
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4answers
320 views

Does a non-buoyant (denser than water) object (such as a lead diving weight) weigh any less when submerged in water?

I've just been discussing this question with my eldest son, who is an extremely intelligent man, as well as being an engineer, a sailor and a scuba-diver, and he believes that an object heavier than ...
0
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3answers
363 views

Man inside an accelerating train carriage [closed]

I'm having trouble recognizing the forces at play here. If we have a man is standing inside a train carriage which is accelerating, and the coefficient of friction (for simplicity dynamic and ...
0
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3answers
139 views

How can you push the ground backwards?

Whenever we come across " The physics behind walking" we often get answers stating that we push the ground backwards then it pushes feet forward and we walk ( very brief answer ) but the ...
17
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4answers
56k views

Is there a general rule for determining the direction of tension force?

Tension, for me, is a tricky thing. After finishing a related chapter of my book and watching a video, I still can't get a hang of it. Here is a situation: My knowledge is that tension, just like ...