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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5answers
294 views

Newton's 3rd law and propellantless propulsion

I was thinking lately about a potential misunderstanding regarding Newton's $3^\text{rd}$ law and the supposed impossibility of creating a device that moves by utilizing just internal forces (...
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3answers
823 views

Inclined plane with friction and a spring

I am given a body with a mass of 1 kg that slides at a constant speed down an inclined plane with an angle of 30 degrees. At the end of the incline there is a spring with a spring constant of 500 N/m. ...
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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. ...
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4answers
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Forces acting while running

If I am running on a surface with friction with no air resistance and also accelerate then net force acting on me is F=ma. The friction acts opposite to direction of motion and is less than the forces ...
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2answers
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Blocks and pulleys problem with friction - the condition for sliding [closed]

I encountered a problem with blocks and pulleys, which I'm not sure about. The diagrams I've drawn are given below. We need to find the minimal mass $M$ of the block $3$, such that block $1$ starts to ...
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Why do we feel weightlessness in water but not on land?

When we draw a Newtonian free body diagram of a man standing still on land, we draw force g and the reaction force. In water when floating still, we still have force g but we also have the reaction ...
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2answers
29 views

Do we ignore weight of the rod in vertical spring-block system?

Problem: The first spring is placed at the middle of the rod and the second one at the end as shown in the figure. If the end of the rod is slightly pulled up and released, determine the angular ...
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3answers
547 views

Bending of a cyclist while taking a turn on a horizontal road

I am a high school student and my teacher taught me that a cyclist bend while taking a turn on a horizontal road because if he doesn't bend it then it will rotate due to net torque of friction about ...
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2answers
391 views

Pressure on each leg - why multiply the area?

Here's the problem (From here): "A large man sits on a four-legged chair with his feet off the floor. The combined mass of the man and chair is 95.0 𝑘𝑔. If the chair legs are circular and have ...
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5answers
108 views

Intuition behind hydrostatic force/pressure being applied laterally

I can understand how the downward vertical force is being applied: due to the weight of the water column directly above it. However, I cannot understand how the lateral and the upward forces act. How ...
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2answers
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Question regarding tug-of-war and tension

I am having a hard time understanding these questions regarding tension$-$ Is the tension in a rope uniform in a tug of war? If yes, then who wins the game? If no, doesn't that violate Newton's ...
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Why does twisting a cork make it easier to remove from a bottle?

When we want to remove a cork from a bottle first we turn the cork. Turning in one direction makes it easier to remove in the axial direction. Does anyone know something more about this?
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Where does the centripetal force come from? How to calculate?

When a bucket filled with water rotates, the water surface will be parabolic( I mean the water is rotating and the water surface is parabolic). Where does the centripetal force of a particle of water ...
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Force on the lower half of the rod by the upper half

I broke the force into two components, along the rod as $T_1$ and perpendicular to the rod as $T_2$. If we see the forces on the lower half of the rod, $$T_2 + \frac{mg}{2}\cos 60° = ma \\ T_2 = -\...
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Reaction force cancels out? [duplicate]

Lets say Im pushing on the wall with a force of 1N. According to newtons laws the wall will push me back with a force of 1N. What I dont get is that my hand already has this 1N of force meaning when ...
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Newtons third law of motion [duplicate]

Im having a real hard time understanding how newtons third law works. Say im accelerating a 1kg ball to 50m/s^2. This means that im applying a force of 50N on the ball. Newtons third law tells us that ...
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4answers
202 views

What happens when a man walks on a canoe? what are the forces acting on canoe and man and how to describe it with law of conservation of momentum?

In my physics class our teacher taught us about this canoe-man problem, where a man walks across a canoe and due to the "law of momentum conservation", the canoe attains a constant $v$ ...
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3answers
60 views

How does friction accelerate a car after rest?

If a car moves using the friction force from the rotation of the wheels, shouldn't a car be unable to accelerate immediately after the car is at motion, since there will be a friction force of equal ...
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Working with ramps and rotational acceleration (friction involved)

Say you have bicycle tire moving with constant velocity. Since the point of contact with the surface remains stationary, so tire will not slide even on an icy surface. But if pushed tangentially to ...
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3answers
80 views

How do pulleys redirect force?

Consider this setup of three blocks, in which you would like to find the acceleration of the 8 kg one: One way I've heard to solve it is to consider the three blocks as one system and look at the ...
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4answers
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How does Newton's third law hold up when a block kept on a table breaks the table?

Suppose there's a block of some mass that is kept on a table. But, instead of staying at rest on the table, it breaks through the table. How does Newton's third law hold up here? If the block is at ...
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1answer
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Two hanging masses connected by springs

I had this problem for a candidacy exam, but wasn't able to get the complete answer. Their spring constants and masses are not the same, find the equilibrium position and frequencies of the system. ...
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5answers
420 views

Doubt relating pure rolling

As we know, when an object perform pure rolling on a plane having friction the friction acts on the edge in the direction opposite to the direction of its translational motion. There are no other ...
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1answer
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On methods to know the type of friction

Suppose 3 blocks are stacked on top of one another and a constant force is applied on the bottom one, how could I know if the friction that is acting on those objects is kinetic or static? Moreover, ...
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4answers
345 views

Friction on a car

I wanted to ask why doesn't the car move on a frictionless surface. Suppose you are on a frictionless surface When you press the accelerator the wheels start rotating and apply a force to the ground. ...
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418 views

In what frame of reference does friction exists?

What is friction? Wikipedia defines friction as: Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. But forces are ...
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332 views

What is the force $N$ and $P$ of the cart and Pendulum for?

I am trying to understand the force present in the system below. I found this picture online and I would like to ask what is the force $N$ and $P$ of the cart and Pendulum for? I tried to google it ...
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60 views

A mathematical analysis of a single fixed pulley

I think Physics stack exchange is correct for this. Suppose we take a simple fixed pulley like this: Suppose the string is inextensible, massless and strong. One end of the string is connected to ...
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4answers
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Physics behind breaking [closed]

A very simple query. Suppose a box rests on a frictionless table. It has a max. normal force of $100 N$, say. Suppose I exert a force of $150 N$, which I suppose is not possible, since normal force by ...
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3answers
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Where would $mg$ act if I consider a man standing on a block and consider the block as my system?

When a man stands on a block, the weight of the man i.e. $mg$ acts downward on the block and Normal reaction $N$ in opposite direction (provided I consider the man as my system). However, if I ...
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2answers
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Is this the right way to calculate the force on a screw?

My brother wants to mount his T.V. to the wall and wants to know if his drywall anchors will be enough. We haven't done any free body diagram analysis in a long time so we just want to know if what we ...
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120 views

Best way to break a rope?

What is a better way to break a rope, two kids pulling from opposite ends, like tug of war, OR , attaching one end of the rope to a wall and then the two kids pulling together. I think the second one ...
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1answer
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Static friction [closed]

Why is this wrong ? My teacher simply said that it is wrong and asked us to solve it by taking cases( The blocks move together or they move separately.),the first case being the blocks move together. ...
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1answer
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How does friction in tires create a centripetal force when turning? [duplicate]

I understand when a car turns, it requires centripetal force and this comes from static friction of the tires. But my question is how? How does friction as in the picture below push outward to the ...
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3answers
52 views

Question about friction, work, and Newton’s 3rd law

So I would like to know the directions of friction acting on the man and the plank in the following situation: The man walks on a rough plank (upper surface rough) kept on a smooth floor. My idea was ...
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6answers
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Non-constant tension in rope

Could somebody explain to me intuitively how tension is not the same in a rope with mass? My physics teacher (when regarding a massless string) told me that the tension is always equal because if you ...
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1answer
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Tension In circular motion

In the below question is given 2 scenarios in which we have to find the tension in two particular cases, A ball is held at rest in position A by two light cords.the horizontal cord is now cut and the ...
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2answers
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How centrifugation can be explained in an inertial frame?

I am reading about centrifugation and I can't understand what forces are responsible for the sedimentation and how the motion of particle can be explained in an inertial frame. I can understand ...
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2answers
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Atwood's machine doubt

The below image is from the book Concepts of physics by H.C. Verma. The last line says that if pulley $B$ is also light then $T_1=T_2$ I don't understand how this happens.
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1answer
42 views

The reaction force of a normal force

Assuming I have a book on a table. First, there is gravitational force acting on the book, which causes the book to also exert the same amount of force on the Earth. Now, the table will also exert a ...
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1answer
53 views

Newton's law doubt

Consider the following arrangement When I drew the FBD of block C then I got a doubt that why tension in string pulling C backwards cannot be equal to force F. I know it is against what actually ...
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1answer
84 views

How does a string pulls pulley at both the ends? [duplicate]

For an Atwood's machine, why does the string exert a downwards force on the pulley that is twice its tension? I'm neither able to understand nor imagine this scenario. How does a wrapped string with ...
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3answers
545 views

Equation of motion - choosing directions for the coordinate axis

I'm not sure this equation is the right one if we invert the direction of the positive $y$-axis. Am I right if we assume the positive direction of the $y$-axis downwards, that the correct equation of ...
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102 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 ...
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1answer
53 views

The Forces Affecting a Sailboat

I've recently read an article about a practical example for " The Forces Affecting a Sailboat " .. I know the standard formula for the wind force which is : Wind force = Wind pressure * ...
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2answers
142 views

How does the system of particles respond to the external force?

If I push a box forward, then probably, the force I apply can be considered external force acting on the system of particles of the box. In rigid bodies like the box, each particle of the body should ...
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2answers
59 views

The purpose of leg drive in the bench press (force body diagram)

A common explanation I've heard for the purpose of the leg drive in the bench press is that the lateral forces generated by the quads off the floor are "converted" into a downward force into ...
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2answers
134 views

Why is it easier to push down a rope from the middle compared to the side?

Intuitively, if I push down on a rope at the middle, I know that it will sink down farther than if I were to press it at the sides. Below I drew a diagram of a person standing on a tightrope to give ...
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3answers
110 views

Why is the rod moving to and from?

These are tow pulleys, and a plastic plank is placed above them which can slide freely. The plank has uniform density and it touches both the pulleys. Both pulleys are placed on the same plane, and ...

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