What is Free body diagram: Definition and 250 Discussions

A free body diagram consists of a diagrammatic representation of a single body or a subsystem of bodies isolated from its surroundings showing all the forces acting on it.
In physics and engineering, a free body diagram (force diagram, or FBD) is a graphical illustration used to visualize the applied forces, moments, and resulting reactions on a body in a given condition. They depict a body or connected bodies with all the applied forces and moments, and reactions, which act on the body(ies). The body may consist of multiple internal members (such as a truss), or be a compact body (such as a beam). A series of free bodies and other diagrams may be necessary to solve complex problems.

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  1. W

    Identifying the Potential Energy of a Spring Pulley System

    Homework Statement Homework Equations U = 1/2 kx2 The Attempt at a Solution So, I took dynamics off campus and needless to say, we didn't really do very much deriving so that aspect of physics really bogs me down and I'm trying to learn it now in another class. So if anyone wants to also...
  2. Frankenstein19

    Free Body Diagram Help: Solving a System of Equations for Forces (PreCalc)

    Homework Statement Homework EquationsThe Attempt at a Solution I got the components of each force. I called the Force from BA "B" and the force from CA "C" and then the force going downward on D "W" FBy=sin30*B FBx=-cos30*B FCy=3/5*C FCx=4/5*C W=-500 ~~~~~~ ΣFx= -B*cos30 + 4/5C = 0 ΣFy=...
  3. C

    Draw a free body diagram for the electric force

    Homework Statement A positive charge Q1=7.4uC is located at a point X1=-2 m, a negative charge Q2=-9.7uC is located at a point X2=3m and a positive Q3=2.1uC is located at a point X3=9 A. Draw a free body diagram for the electric force acting on Q1, Q2, and Q3. B. Find the magnitude of the force...
  4. S

    Calculating Distance: Free Body Diagram for Box Sliding with Friction

    Homework Statement A 250 kg box slides down the ramp and then across a level floor. The coefficient of kinetic friction along the floor is 0.20. A person see the box moving at 1.0 m/s(left) and pushes on it with a horizontal force of 140 N (right). How far does the box travel before coming to...
  5. B

    Free Body Diagram and directions

    Hi everyone, I am an electromechanical engineering student. The last few days I am trapping into some confusion about some things. I am just going to state my question underneath. Question: First question: As they learned me at the university. When you draw a free body diagram it doesn't mind...
  6. S

    Pressure force in water on truncated cone with air inside

    Homework Statement Consider the truncated cone tank submerged in water: inside the truncated cone tank there is air. Evaluate the forces acting on the truncated cone tank. Homework EquationsThe Attempt at a Solution The forces are the following Boyuant force : $$F_b= \rho_w g V_{tank}$$...
  7. E

    How do I use a free body diagram in this case?

    In the above cases I want to find the acceleration a for m1. I can do it by considering m1 and m2 to be a system, which would give me a = F/(m1+m2). How can I use a free-body diagram instead to calculate the acceleration? Using a free-body diagram, m2 only affects the vertical motion by exerting...
  8. E

    Basic Forces & Bolts: Getting Started on Homework

    Homework Statement Homework Equations sum of forces in x and Y = 0 sum of the moments at a point = 0 Ffr = normal force * friction coefficient The Attempt at a Solution Im just trying to make a start, I am struggling to wrap my head around the basics with this question. Do you guys think...
  9. T

    Determining the Free Body Diagram for a Dolly & Trailer

    Homework Statement The context of this problem involves a dolly pulling a trailer, and I am trying to establish the basic free body diagram for the trailer. Is what is done so far acceptable and is this a step in the right direction? Homework EquationsThe Attempt at a Solution I am confident...
  10. N

    Concrete Block Incline acceleration question

    Homework Statement A concrete block of mass 25kg is placed on a smooth slope that makes an angle of 30 degrees with the horizontal. Ignoring the effects of air resistance, calculate a) the acceleration of the block as it slides down (g = 9.81 ms-2) b) the distance the block moves in 3 seconds...
  11. Z

    Challenging Free Body Diagram Problem (Statics)

    1. Homework Statement Given the picture, find theta, and the magnitude of the force going from point A to B. I have asked multiple people how to solve this problem and they have no idea, I end up getting 2 equations with 2 unknowns but then when I try to solve for theta I get 70cos(theta) -...
  12. C

    How do I draw a free body diagram of a car on a slope?

    Homework Statement A car attempts to accelerate up a hill at an angle θ to the horizontal. The coefficient of static friction between the tires and the hill is µ > tan θ. What is the maximum acceleration the car can achieve (in the direction upwards along the hill)? Neglect the rotational...
  13. Z

    Work and Kinetic Energy of a Sled

    Homework Statement A man pulls a 15-kg sled containing a 5.0-kg dog along a straight path on a horizontal surface. He exerts a force of 55 N on the sled at an angle of 20.° above the horizontal, as shown in the figure above. The coefficient of friction between the sled and the surface is 0.22...
  14. W

    Easy Free Body Diagram Question

    Homework Statement Draw the free body diagram of the system. (I know that's not what the problem is, but that's what I need clarity on) Homework EquationsThe Attempt at a Solution So I drew the same thing, more or less, but for mine Ay went up. This was how a very similar problem was done -...
  15. C

    Truss Free Body Diagram & initial conditions

    Homework Statement Complete a free body diagram for the truss structure with a weight attached to node 2 (this is known as 151N) Homework EquationsThe Attempt at a Solution I have attached my Free Body Diagram The diagram is to display what is know at the start of the problem before working...
  16. O

    Why is Block B not experiencing a normal force in this static friction problem?

    Homework Statement How come for the following image when I assume block B slips up, block A does not move. The free body diagram at block B does not have a normal from the ground. This is a static friction problem. [/B]Homework Equations No relevant equations all theory[/B] The Attempt at a...
  17. Racer_Rob

    Free body diagram for a sliding contact

    Homework Statement Component A is pushed vertically down with a known force F into component B. The angled surface of B is parallel to the angled surface of A. The contact between A and B is rough and so is the contact between B and the ground. The coefficients of friction are known and so is...
  18. I

    Calculating reaction forces on 3d object

    Hello all, I am in the process of calculating reaction forces on an object, and need some help. Attached is a free body diagram of an object in two different views- one looking from the sides (z-x plane) and one looking it in birds eye view. (xy plane) 7 variables I am looking to solve are...
  19. J

    Help please -- Free body diagram for a weightlifter?

    Homework Statement A weightlifter stands up at constant speed from a squatting position while holding a heavy barbell across his shoulders. Draw the free body diagram of the lifer using Fg, normal force, and force by barbell Homework Equations Fnet=0 ? The Attempt at a Solution I tried...
  20. Mr Davis 97

    Representing Free body diagrams

    I have a simple question. I know that the objects that we work with in introductory physics are point particles. Thus, say we have a picture frame that is put on a wall. There is a wire holding it up, where the wire is attached to the top right and the top left corners of the frame. The passes...
  21. W

    Solve Truss Joints Using Method of Joints

    Homework Statement Determine the axial forces in the members of the truss and indicate whether they are in tension or compression. Homework Equations Fx = 0 Fy = 0 Mp = 0 The Attempt at a Solution I attempted to find the reactions at the supports first. So: Fx = 0 = Bx + 800cos(250)N Fy...
  22. W

    How Do You Calculate the Reactions at Supports in a 3D Equilibrium Problem?

    Homework Statement The 1.1m bar is supported by a ball and socket support at A and 2 smooth walls. The tension in the vertical cable CD is 1kN. Draw the Free Body Diagram of the Bar. Determine the Reactions at A and B. Homework Equations Equillibrium equations. Perhaps the vector...
  23. W

    Free body diagram of pin support and cable

    Homework Statement A) Draw a free body B) determine the tension in rope A and the reactions in B. Homework Equations [/B] Standard equilibrium equations The Attempt at a Solution My free body shows a collinear force T through the rope, the given downward force at 5ft, and then a Bx and By...
  24. DanielleG

    Centripetal Force Theory Questions

    Homework Statement Answer True, False, or Cannot tell to each of the five statements below. A small projectile is launched horizontally 1 m above the surface of a smooth, airless planet, with sufficient speed for orbit. A bug riding in a small hole in the projectile has apparent weight...
  25. T

    What are the equal-and-opposite forces of friction forces?

    Homework Statement A block rests on a table, and a second block, connected to the first with a rope, hangs over the side of the table. See the illustration. (Assume the pulley is massless and frictionless.) All objects pictured are stationary. Identify every force involved in the pictured...
  26. N

    Force & Motion Homework: Force Diagrams, Velocities & Accelerations

    Homework Statement A small box (mass m1) is placed upon a large box (mass m2); the large box i placed on a horizontal table. The boxes begin a rest on the table. The lower box is hit by a horizontal blow at the time t=0 resulting in a initial velocity v0. The frictioncoefficient between all...
  27. B

    Problem with making the correct FBD

    Homework Statement Consider a wedge of mass ##m## whose upper surface is a quarter circle and is smooth. The lower part is rough. A small block of same mass is kept at the topmost position and the initial position is shown in figure. The block slides down the wedge. Find the minimum value of...
  28. A

    Maximum weight a bar and cables can hold before breaking

    Homework Statement A weight W is supported by bar AO and cables AB, AC, and AD. Point A lies in the xy plane, if the bar and cables have the strengths listed below, determine the largest value W may have. Hint given: A FBD of joint A is recommendedto being this problem. Bar AO should be...
  29. A

    Force needed to support Suspension of a Vehicle

    Homework Statement A model for the suspension of a vehicle is shown where the spring has stiffness k = 178 N/mm and an unstreched length of 347 mm. http://imgur.com/1dTVs12 Determine the value P and the force supported by member AB so that the suspension has the equilibrium position shown...
  30. W

    Setting up systems of forces and free body diagrams

    Homework Statement Suppose I've got a static mass on a downward plane. (For instance a car on a drive way). How would you set up this free body diagram? Homework Equations F = f1+f2...etc The Attempt at a Solution My preference is A, but I've seen it displayed in examples in my book as B...
  31. A

    Statics: four crates, four springs, free body diagram

    Homework Statement In figure (a), four identical crates weighing 2,000 lb each are stacked one on top of another, and in figure (b) a simple model for determining the deformation of the stack of crates is shown. In this model, each spring has the same stiffness k = 4,500 lb/in. and the forces...
  32. A

    Equilibrium of a Collar and Pulley System with Spring - Free Body Diagram

    Homework Statement A collar with a pulley slides on a frictionless vertical bar GH. A string A B C D is wrapped around, where portion AB of the string is horizontal. A spring with 2.5 lb/in. stiffness is placed between the collar and point H. The spring has 7 in. unstreched length and 5 in...
  33. A

    What is the force required to keep two blocks in equilibrium

    Homework Statement Blocks A and B each weight 170 lb and rest on frictionless surfaces. They are connected to one another by cable AB. Determine the force P required to hold the blocks in the equilibrium position shown and the reactions between the blocks and surfaces. Hint given: This...
  34. A

    Finding largest value of H of a ramp, from a FBD

    Homework Statement The dimension h is to be determined to that a worker can comfortably slides boxes weighing up to 106 lb up and down a frictionless incline. If the worker can apply a 50 lb horizontal force to the box, what is the largest value h should have? Hint given: Before taking any...
  35. L

    Free body diagram drawing for a two force members on machine

    Homework Statement When a force of 2 lb is applied to the handles of the brad squeezer, it pulls in the smooth rod AB. Determine the force P exerted on each of the smooth brads at C and D Homework Equations ##\sum F_x=0## ##\sum M=0## ##\sum F_y=0## The Attempt at a Solution I drew a free...
  36. monsteruf

    Free body diagram for all forces

    Homework Statement Two ropes are connected to a steel cable that supports a hanging weight as shown in the figure. Draw a free-body diagram showing all of the forces acting at the knot that connects the two ropes to the steel cable. Draw the force vectors with their tails at the knot. The...
  37. E

    Free body diagram of a wheel driven by a motor

    Neglecting drag, I'm trying to understand how a wheel driven by a motor on a level surface rolls without sliding and experiences constant velocity. I'm trying to construct a free-body diagram. The wheel has a weight and a normal force acting on it in the vertical directions. The sum of...
  38. C

    Magnetic force to hold machine and required Torque to drive

    Homework Statement The robot crawler has a magnet attached to it. The idea is to get the crawler up the wall. What is the magnetic force required to hold a object (in this case) a robot crawler with an attached Magnet? Is more magnetic force required to hold the crawler while it goes up the...
  39. T

    What is the Sign Convention for Moments in Free Body Diagrams?

    Homework Statement In the picture, I am confused with the sign of the moments. When taking moments about D, the moment due to the 100N is taken as positive, but when they take moments about B, its negative. Homework EquationsThe Attempt at a Solution Shouldn't both cases be negative since in...
  40. D

    MHB Free Body Diagram Explained: Why is Right FBD Upward?

    Can you explain why the free body diagram of each members are as shown? I kind of understand why the FBD of the member on the left is drawn as shown. But the FBD on the right is confusing, Why does it have a component in Y (upward) direction? thanks!
  41. D

    (Vector statics) Effect of a pulley on free body diagram?

    For example, a 1-m bar fixed to a wall holding a weight of 100 N, like this: How will the free body diagram of the second case different from the first?
  42. C

    Free Body Diagram of a ice skater?

    Homework Statement In our science class, we had to draw a free body diagram of an ice skater. The ice skater pushes against a force plate and that results in her skating in the other direction. (Newton's third law of motion). We have to use Newton's three law of motions to explain this...
  43. T

    Help with free body diagram for a pendulum

    Homework Statement I want to sum the forces perpendicular to the pendulum and sum the moments about the pendulums center of gravity. Homework EquationsThe Attempt at a Solution P\sin \theta - mg\cos \theta - N\cos \theta = -m\ddot x\cos \theta + ml\ddot \theta -Pl\sin \theta - Nl\cos \theta +...
  44. K

    Free body diagram of a beam construction

    Homework Statement Beams AC and BD are light (no mass) and they're conjoined at B. Points A and D are fixed but frictionless. The radius of the wheel is R and the weight hanging on the pulley has the mass m. Homework Equations Fx=0 Fy=0 M=0 The Attempt at a Solution I'm stuck at the very...
  45. nate crosby

    Free Body Diagram -- forces on a structure over a balcony wall

    Hi, I am trying to work out the forces involved at the contact points in a design of a structure over a balcony wall. I have drawn up the cross section of the situation equilibrium, with a tolerance. I want to find out what forces will be acting on the structure and the balcony wall when a...
  46. S

    What causes drag on a stationary car?

    See attached photographs. For the car problem, I think the drag should be smaller than the forward acceleration but I'm not sure. For the Rocket question, I am pretty sure I am correct but I'm not sure why. The drag and the weight would both be in the down position.
  47. T

    Free Body Diagram of Car on Mountain

    If a car is on top of a mountain moving with an initial velocity, will it only forces acting on it be the normal force counteracted by the force due to gravity?
  48. U

    How Do You Balance Forces in a Bicycle Free Body Diagram?

    Homework Statement Bicycle with a rider applying weight to on pedal. Draw as free bodies in equilibrium. There are different situations. Homework Equations N/A The Attempt at a Solution So I am working on part a). 1. I believe it is only referring to just the pedal, chain, and the two...
  49. kiwimia

    Help on a free body diagram and equation

    1. Relevant information This is a two-block-system on top of each other to the right side of a wall, both attached with springs that are also attached to the wall. A force is applied on the bottom block to the right direction, frictions occurred on both bottoms of the two blocks. Here is the...
  50. S

    Free body diagram of an incline

    Homework Statement For the maximum angle for which you have data draw a free body diagram and explain how the forces add to give the resultant (net) force and show the calculations required to determine the acceleration. The lab was about using Galileo's inclined plane to measure acceleration...
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