# What is Free body diagram: Definition and 249 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. ### Formula derivation connecting vertical water flowrate & horizontal distance moved by a suspended sphere

TL;DR Summary: I am Highschool student writing a 4000 word research paper on Bernoulli's principle and the coanda effect. I need help with derivation of a formula that connects flow rate of water and distance moved by the sphere in my experiment. I am a high school student writing a 4000 word...
2. ### Distributed weight of inclined beam.

I'm having problem in drawing the distributed load (weight per foot) for the inclined beam as it shows. should it be rectangular? if so shouldn't the distributed load be vertical down as the resultant weight at the centroid (W) please help me understand how to draw the free body diagram for this...
3. ### B Elevator Question -- What does a downward acceleration mean?

If an elevator is moving upward, what does a downward acceleration mean? When applying the free body diagram, will the positive direction be upwards since the elevator is moving up?
4. ### Free body diagram for two-force members

Hoping someone can chip in and help me understand a problem when it comes to two-force members. I have a structure as shown below. Essentially its a single body attached at 3 points with pin joints. My question is, is it appropriate to treat each of the left and right side as individual...
5. ### Engineering Is My Free Body Diagram for a Frame Accurate?

can you check if I sketched it correctly? And please if you know any good resources refrence it.
6. ### B Question about a simple free body diagram

In this diagram, if the system begins by being held static, and then at time ##T## release of all components occurs, at all times ##>T##, until vertical movement stops upon vertical block ##m## making contact with the Normal Force at the base of block ##M##, will the lateral acceleration of...
7. ### Free body diagram for an inverted pendulum in the rolling sphere

So, to obtain the motion equations I initially plotted the free-body diagram (see picture). Then I’ve tried to get equations, but I’m not sure, do I have done it rightl. I will be gratefull if someone could help me.
8. ### I How can you make a free body diagram for someone running then sliding?

Let's say you are riding a bike very fast, and then you sharply turn into a slide (where the bike is sliding perfectly sideways). I'm trying to calculate the angle that the bike would be leaning at, but I'm having trouble creating the free body diagram. Right now I have the normal force and...
9. ### Free Body Diagram for a Piece of Gum on the Underside of a Desk

So I’m a high school physics teacher and I came up with the question above. However I haven’t given it to my students because I’m not sure what the answer would be. There is a force holding the gum up, and that force must balance the force of gravity. I’d probably call that an applied force, so...
10. ### Finding Radial Force from Free Body Diagram

I have a question regarding a homework exercise. My professor asked me to find the radial force in the free body diagram in the image included. There is a weight Fz from above and it is assumed that it is countered by the vertical component of both the Ff (friction force) and the Fn (normal...
11. ### Automotive Vehicle Parking Brake Test on a Slope [How Convert to a Flat Ground test?]

Vehicle Mass : 3 tonnes Manufacturer's instruction is to test vehicle's parking brake effectiveness is to engage parking brake on 30.96 degrees slope. If it holds, it is effective. I do not have 30.96 degrees slope & I want to replicate the same test on flat ground. I was thinking of...
12. ### Free body Diagram of a Plank resting on two Cylinders

I have put a picture of the problem above. The picture below shows my free body diagram. Fg is the component of the gravitational force in the direction fo the tangent at the point of contact and Ff is the frictional force between the plank and cylinder. I put Ff in the opposite direction as Fg...
13. ### Shear Force on Bolts mounting gearbox to engine

Hello, I have designed a gearbox that bolts on to a fixed engine and fixed pump. It is completely supported by them. The total mass of the gearbox and the components attaching it to the engine and pump is 7.7kg. Its centre of mass is 0.167m along the x-axis and 0.09m along the z-axis from the...
14. ### Value of frictional forces in a 3-block system

So I started by checking the options.I substituted the value of friction in the equations I got by making free body diagrams.I got different value of Tensions.For 1 and 3 Tension came to be 38 N.For 2 Tension came out to be 42N and for 4 Tension came out to be 40 N. Now I think that I will take...
15. ### Free body diagram -- Ball rotating on one arm of a Y shaped pole

To start off with, I can't seem to interpret the FBD here. Here are my drawing: and what I interpret as. From here, I feel like I can (it's wrong obviously but I'm not sure why) state that sin theta = o/h = o/mg = N/mg , so N= mg sin theta? Thanks
16. ### Need Help with Free Body Diagram of Oil & Gas Packer Tool

Has anyone created a thread on Free Body Diagram on assembly having many components ? For example a Casing having premium threads in both end and a set packer within it. What would be the FBD equations to determine various forces and reaction forces
17. ### Is the Normal Force on m2 Affected by Vertical Acceleration in Different Cases?

I want you to tell me if I'm right For 1), does ##m_2## feel a normal force? Because I don't think so, since it isn't pushing the wall. For 2), ##m_2## suffers a normal force because it feels a pseudo-force to the left and so it pushes the wall
18. ### Free body diagrams for boxes, inclined planes and springs

FIRST PICTURE I have some doubts here because of the spring... I'll tell you what forces I've drawn. For ##A##, I drew the weight and the force applied by ##B## (the normal force) on the vertical axis; and the elastic force pointing to the right on the horizontal axis. For ##B##, I drew the...
19. ### Draw the F.B.D. (Free Body diagram) of two blocks

Summary: In the situation given, all the surfaces are friction less, pulley is ideal and string is light, F=mg/2, Find the acceleration of block 2 ? Here's the diagram-- My attempt- (i) I tried to solve the question by making FBD of the two blocks, but i am not able to draw all the forces...
20. ### Understanding Free Body Diagrams: Explaining the Forces on a Compressed Board

Hello everyone. I find the following problem confusing. A board sandwiched between two boards in the figure below weighs 95.5N. If friction exists between the middle and the compressing boards, draw the free body diagram of the middle board. Below I attached the diagram found in the solution...
21. ### Analyzing Forces & Electrons: Free Body Diagram

Hi i am posting this to double check my work. Please help and feel free to ask any questions. I posted a picture of my work and what i currently have. 1. Homework Statement Two small insulating objects are hung from strings attached to the ceiling. The masses of each object is 0.0076 kg. The...
22. ### Statics problem (moment and equilibrium)

1. Having really hard time understanding the concept of moment and equilibrium in statics. In the following picture the man is carrying a 6kg uniform rigid board. I'm asked to calculate the amount of force the man feels on his shoulder. (at point A) Now I know I'm supposed to start by making...
23. ### What are the equations for circular motion on a Ferris wheel with R2D2?

Homework Statement 3. Consider R2D2 (a droid) with mass 30kg riding on a Ferris wheel with diameter 25m, with a velocity of 2.8m/s. a) Compute the free body diagram for R2D2 at the exact top, exact bottom and at both horizontal positions. Remember to include gravity. (Note: The forces act in...
24. ### Free body diagram on a block pushed against a ceiling

Homework Statement A 2kg block is being pushed along a ceiling with friction by an angled force of 70 degrees. I'm asked only for the free body diagram. Homework EquationsThe Attempt at a Solution I figured both the gravitational and normal force would point downwards, but the force applied at...
25. ### Create the free-body diagram for the scenario below.

Homework Statement A Mercedes-Benz 300SL (m = 1700 kg) is parked on a road that rises 15 degrees above the horizontal. What are the magnitudes of (a) the normal force and (b) the static frictional force that the ground exerts on the tires? Important: Assume that the road is higher up to the...
26. ### Finding the force on a cord from a pulley

(Mentor note: moved from General Eng hence not homework template) This is the given scenario. I'm trying to find the 'String R (lower part)' force. I know every other variable (the angles, string L and string R and the Rectangle is a mass m). Any help would be appreciated!
27. ### Calculating Free Body Diagram Forces

On EngineersEdge.com they have a free body diagram of a scissor lift https://www.engineersedge.com/mechanics_machines/scissor-lift.htm Can anyone explain how the Fy, Fx components are determined? What is specifically confusing to me is how Fy is opposite in direction given the system. To me...
28. ### Force Calculation -- Hydraulic cylinder and a rotating arm

Hi There, Long time reader, first time poster.. I hope someone out there can help me. I'm designing an add-on to an existing piece of equipment and I'm unsure of how to calculate the resultant force output from a hydraulic cylinder. On a straight push, the chosen hydraulic cylinder has an...
29. ### Determine the forces acting on the two rods - Free body diagram

Homework Statement Determine the forces acting on the two rods in the figure. Explain which stresses that act on the rods and the bolts holding the rods to the brackets in point A and C. Homework Equations ∑Fx = 0 ∑Fy = 0 ∑Fz = 0...
30. ### [Calc] Sign Convention in damping spring system

Homework Statement A carriage is mounted on a spring, as shown in the diagram. The bottom of the spring is fixed to the ground. The carriage (loaded with its passenger) has a mass of 150kg. The carriage can only move vertically. The natural length of the spring is 10m and its spring...
31. ### Free body diagram of a preloaded system with a gasket

Hello,Ive got a question and wondering if there is someone that could help me? I would really appreciate it! I am studying for an exam that I am going to have in a couple of weeks and it has been going great besides that I have been stuck on a question about tension in a preloaded system with a...
32. ### Statics problem free body diagram

Homework Statement Homework EquationsThe Attempt at a Solution why are my reactions at A considered wrong? I know that AC and DC are two force-members
33. ### Statics free body diagram (frames and machines)

Homework Statement Homework Equations Trying to find the reaction forces at E. But, I am kinda confused about drawing the free body diagram for each member. I know that member AD and CB are two force members. What is wrong with my free body diagram then? The Attempt at a Solution i...
34. ### How can I draw a free body diagram of a rotating wheel?

I am currently performing failure analysis on an A356 Aluminum alloy wheel subjected to rotational loading, with a maximum load of 650 kgf and a torque of 4600 Nm. Cracks formed in the wheel after 1.3*10^6 rotations. My job is to perform a stress analysis to determine the regions of maximum...
35. M

### Forces and Free-Body Diagrams in Real-World Scenarios

Homework Statement I am just going over my class notes and I just wanted to clear up a few concepts regarding forces and free-body diagrams -- I'm either missing some forces or adding one too many: Identify the forces acting on objects in each of the following situations and draw a free-body...
36. A

### Spring angles at static equilibrium on application of force

Homework Statement Two linear springs with stiffness Kh, Kv are attached to a single mass m at right angle to each other, i.e; one of the spring(Kh) is in the horizontal direction(x-axis) and the other(Kv) is in the vertical direction(y-axis). A constant force F is being applied to the mass...
37. F

### Direction of friction on two stacked boxes

Homework Statement Solve the free diagram of two stacked boxes on a frictionless table accelerated by a force. Homework Equations [/B] None The Attempt at a Solution I have box 2 stacked on box 1. Box 1 is on a frictionless table and accelerated by a force. However, there is friction...
38. ### Finding the magnitude of the force

Homework Statement A force F is applied on the bigger mass 'M', which results in the prevention of smaller masses M1 and M2 moving with respect to larger mass M. The mass 'M' slides smoothly on the frictionless surface. Find the magnitude of the force. The pulley is ideal also consider the...
39. ### Calculating Reaction Forces on Cylinders Resting on an L Profile

Homework Statement Two cylinders, each with a mass of 10kg, are lying on an L profile. Neglect the thickness and weight of the L profile. Calculate the reaction force in b and e. Homework Equations G = mg The Attempt at a Solution So I tried to make a free body diagram of the cylinders. I...
40. ### Free body diagram of a sailboat

This is a practical issue I've trying to resolve by understanding the physics. While I talk sailing jargon, ultimately this is a question of simple torsional forces on a body. So: In a high wind, when heeled over, my boat does what's called "rounding up"; it turns sharply into the wind -...
41. G

### Calculating Forces on an L-Bracket for Supporting Large Pipework

I am installing an L-shaped bracket into a brickwork chimney to support some large pipework. I am trying to work out the forces in each fixing to ensure that I won't be pulling the bracket off the wall once the pipes are filled with water. I've tried drawing the free body diagram and to resolve...
42. ### Simple bending moment calculation

Hi, Really need some help with figuring out the max bending moment in the diagram shown below (I'm aware this is extremely simple but time and stress appear to have the better of me, so any help is appreciated) I think I've worked out the reactions at each support by doing m=wL as the...
43. ### Free Body Diagram of 3-Bar Linkage. Splitting the force?

Homework Statement Hi, please see the attached file. I am trying to find the force as illustrated in the diagram. Homework Equations [/B] The Attempt at a Solution I've found the force for the 4deg beam and therefore the horizontal beam however I am unsure how to take into account the...
44. ### Free Body Diagram lab report -- General Question

< Mentor Note -- thread moved to HH from the technical forums to use a scpecific schoolwork problem to illustrate the general concept of torque in a FBD > I'm writing up a lab report for Physics class and I have to draw FBDs for torque being applied to a ruler resting on a pivot point. I've...
45. ### Rolling Pendulum: Solving the Dynamics Equations

(This is NOT a homework problem. It's an engineering problem I'm trying to crack.) A wheel with a rubber tire (friction) can roll on a suspended rail. Attached to it is a pendulum that's rigidly mounted on the axle of the wheel with a mass that can hand down and swing. (The wheel's rotation...
46. ### Having a hard time writing equations of motion....

Homework Statement [/B] Homework Equations The Attempt at a Solution [/B]
47. ### What would the Free Body Diagram of a Trebuchet look like?

What would the Free Body Diagram of a Trebuchet look like (FOR THE SYSTEM)? Would it be comparable to a see saw/ teeter totter? I am aware of some of the forces at play, but I feel there is some I am missing.
48. ### Ice on an inverted bowl: Radial force?

Hello! I am just stuck on one part of this question and would be grateful for any help. Question A small block of ice slides from rest from the top of an inverted frictionless bowl of radius R (above right). How far below the top x does the ice lose contact with the bowl? Equations mgx =...
49. ### Free body diagram of two different objects

I was wondering if anyone can provide feedback on my free body diagram of two objects acting on each other. The question is asking for two separate free body diagrams. A force is applied to object 1, and object 1 pushes against object 2. Object 1 is on wheels and object 2 is in contact with the...
50. ### 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...