What is Statics: Definition and 902 Discussions

Statics is the branch of mechanics that is concerned with the analysis of (force and torque, or "moment") acting on physical systems that do not experience an acceleration (a=0), but rather, are in static equilibrium with their environment. The application of Newton's second law to a system gives:






F


=
m


a



.


{\displaystyle {\textbf {F}}=m{\textbf {a}}\,.}
Where bold font indicates a vector that has magnitude and direction.





F




{\displaystyle {\textbf {F}}}
is the total of the forces acting on the system,



m


{\displaystyle m}
is the mass of the system and





a




{\displaystyle {\textbf {a}}}
is the acceleration of the system. The summation of forces will give the direction and the magnitude of the acceleration and will be inversely proportional to the mass. The assumption of static equilibrium of





a




{\displaystyle {\textbf {a}}}
= 0 leads to:






F


=
0

.


{\displaystyle {\textbf {F}}=0\,.}
The summation of forces, one of which might be unknown, allows that unknown to be found. So when in static equilibrium, the acceleration of the system is zero and the system is either at rest, or its center of mass moves at constant velocity. Likewise the application of the assumption of zero acceleration to the summation of moments acting on the system leads to:






M


=
I
α
=
0

.


{\displaystyle {\textbf {M}}=I\alpha =0\,.}
Here,





M




{\displaystyle {\textbf {M}}}
is the summation of all moments acting on the system,



I


{\displaystyle I}
is the moment of inertia of the mass and



α


{\displaystyle \alpha }
= 0 the angular acceleration of the system, which when assumed to be zero leads to:






M


=
0

.


{\displaystyle {\textbf {M}}=0\,.}
The summation of moments, one of which might be unknown, allows that unknown to be found.
These two equations together, can be applied to solve for as many as two loads (forces and moments) acting on the system.
From Newton's first law, this implies that the net force and net torque on every part of the system is zero. The net forces equaling zero is known as the first condition for equilibrium, and the net torque equaling zero is known as the second condition for equilibrium. See statically indeterminate.
A physicist who does research in statics is called a statician.

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  1. C

    Statics: Determine the magnitude of the resultant force

    [b]1. Homework Statement : The Attempt at a Solution I keep attempting this problem and so far I have got this: F1x: 150 F1y:260 F2x:424 F2y:424 F3x:600 F3y:250 Then I add the x's together and y's together, square both and take the square root for magnitude, but can't seem...
  2. A

    Vector Mechanics Statics question

    In the question I am not able to understand what the scenario is. Is it that we are removing the P force after insertion? If that is the case, both the normal and the friction forces will change after removal of P. Then how can we calculate. Please help, I am going to have my exams tomorrow.
  3. A

    Statics - Finding Reaction at Supports

    Hey I'm just going over a past paper and I've lost the section of my notes RE this topic. I understand how to draw the free body diagram when there is a pin involved, but not when it is connected at 4 points, the fact that they're at an angle is not helping. Any help greatly appreciated...
  4. A

    Solve Vector Statics Problem - Need Help Now

    I am not able to figure out how to solve this problem. It does not seem to be a statics problem to me. At what point do we consider the equilibrium. Please Help!
  5. A

    Mechanics question on vector statics

    Determine the reactions at B and D when b = 60mm ? (Diagram is attached) Since B and D are hinged we don't know the direction as well as magnitude of the reaction forces at B and D. Hence we have 4 unknowns (Bx, By, Dx, Dy). But I can't find 4 independent equations. I got three by ƩFx= 0...
  6. K

    Statics equilibrium question

    Homework Statement Question: The plate shown, picture is attached, is subjected to force F and 3 reaction forces R1 R2 R3. Find R1 Homework Equations equations of equilibrium: sum of Fx = 0 sum of Fy = 0 sum of moment about point O = 0 The Attempt at a Solution sum of Fx =...
  7. J

    Equivalent Force Systems: Statics Review

    I know how to approach this problem. First, I will need to find the reactions at the supports. Then apply Joint or Section Cut Method to find the forces acting between the members. Then take the force acting on member b0b1 and plug in Euler Buckling equation, while choosing the correct...
  8. A

    Statics - Pin jointed structure - Equations of equilibrium and reactive forces

    Homework Statement Using the pin-jointed structure in the image: a) Set up ALL equations of equilibrium for the structure. b) Determine ALL reactive forces within the structure, including the directions and locations where they act. I have attempted the problem however i can't seem to find a...
  9. H

    Statics and Dynamics problem

    Homework Statement You are working for the Peace Corps in a developing country. Your job is to design a simple, but accurate scale for weighing bulk materials such as food and construction materials. A possible idea consists of a loading platform, D, that is supported by cable AB, where end...
  10. M

    How Do You Solve a 2D Statics Frame Problem with Multiple Unknowns?

    Homework Statement I will attach a scanned pic of the problem, but it seems to be a basic frames problem. However, everything seems to have to many unknowns on it to solve. I feel like I'm missing something simple, but I can't seem to make any more progress. Homework Equations ƩM=0...
  11. J

    Need help clarifying statics problem.

    http://postimage.org/image/8i5i2dtgr/ http://postimage.org/image/8i5i2dtgr/Homework Statement What is the magnitude of the internal force in member BC?Homework Equations So I figured out the reaction force at A and D by taking the moments about point A to find the vertical force at D and then...
  12. D

    Statics: Magnitudes/Resultant force

    Homework Statement I'll attatch it. The Attempt at a Solution Alright, so I work out the angle of the right side... cos-1(12/13) = 22.6° Find the components of the right side... F1x = 800cos(40) = 612.84 F1y = 800sin(40) = 514.23 F2x = 600cos(22.6) =...
  13. S

    Statics Truss Problem, Stuck at force in one member. Please help

    Homework Statement Figured it would be easier if I showed a picture http://img210.imageshack.us/img210/707/problemcz.jpg Homework Equations Ʃm=0 Ʃfx=0 Ʃfy=0 The Attempt at a Solution Here is my attempted solution, I am missing member BD and not sure which way to solve it, I...
  14. W

    STATICS truss/ math equation - joint by joint

    studying for my test, I have a truss joint equation with 2 variables ƩFx = 0 : 4/15 (15kN) - 10/10.44(Fbd) - 4/5(Fbe) = 0 12 = .957(Fbd) + .8(Fbe) ƩFy= 0 : 3/5 (15kN) - 6kN - 3/10.44(Fbd) + 3/5(Fbe) = 0 6 = 9 -.287(Fbd) + .6(Fbe) -3 = .287(Fbd) + .6(Fbe) this is where I'm...
  15. X

    Statics struss tension/compression

    Homework Statement see attachment Homework Equations The Attempt at a Solution Why is DG, DE in tension while HG is in compression according to the FBD? How did the book determine this? Do you just randomly guess tension/compression and then do the calculations and see if you get...
  16. X

    Is the Strut a Two Force Member? Why is Only One Force Used in Calculations?

    Homework Statement see attachment Homework Equations The Attempt at a Solution The book says the strut is a two force member. Why then isn't there a equal but opposite direction force Fba at point B? Isn't that what a two force member means? Why for this two-force member only the force at...
  17. J

    Statics Problem: hanging disk, tensions etc.

    Homework Statement The circular plate has a weight W and a center of gravity at its center. If it is supported vy three vertical cords tied to its edge, determine the largest distance d from the center to where any vertical force P can be applied so as not to cause the force in anyone of the...
  18. X

    Statics free body diagram concept question

    Homework Statement See attachments Homework Equations The Attempt at a Solution In the explanation attachment, I don't get the last paragraph "Note that force Fce acts downward on bar...compression." Since from the figure Fce is pointing down, and Fbd is pointing up, shouldn't...
  19. B

    Basic statics question on shear moment equation

    Sorry, I meant to title it "Basic statics question on bending moment equation." Oh well. Homework Statement Problem F7-7 http://www.scribd.com/doc/94480961/Chapter-7-Fundamental-Problems Homework Equations Summation of the forces in y, summation of the momentsThe Attempt at a Solution I...
  20. V

    Statics problem about an anchored plank in water

    Hello, I'm new and quite unfamiliar with all the conventions, but I'll use underline for vectors since I couldn't find the proper thing (is the convention to use bold here?) Problem: No more.Relevant equations: Fnet = ma = 0 τnet = Iα = 0 τ = r x F = rFsinθ Fbuoyancy = ρwaterVgAttempt at...
  21. S

    Solving a FRAMEwork Static Problem - Find Correct Solution

    [b]1. every member is 0.45m and all the angle is 45degree... C is fixed support, D is roller support [b]3. Ʃfx = 0 , Cx = 0 Ʃfy = 0 , Cy + Dy = 20N ƩMc = 0 , 20(0.45) + Dy(0.45) = 0 Dy = -20N...
  22. K

    Statics Allowable load problem.

    Homework Statement Determine allowable load on steel tube L= 14 in A= 11 in ^2 Es= 30 x10^6 θ=24,000 psi δ= .008 Homework Equations δ=PL/EA θ=P/A The Attempt at a Solution .008=P(14 in)/(30 x 10^6)(11 in)^2 P=188571.4 lb θ=P/A 24,000 psi=P/11 in^2 P=264,000...
  23. J

    Statics: Reactions at rocker and pin on an A-shaped frame

    Homework Statement Determine the reactions at rocker support A and pin support B.Homework Equations ƩF = 0 ƩM = 0 The Attempt at a Solution ƩFx = 0: -Asin(25) - (800lb) + Bx ƩFy = 0: Acos(25) - (500lb) + By I'm getting thrown off because of the rocker on an incline.
  24. H

    How to Solve a 3-D Truss Problem: Finding Forces at a Specific Point

    Homework Statement FIND A FORCE OF A 3-D TRUSS Homework Equations ƩFX=0 ƩFY=0 ƩFZ=0 The Attempt at a Solution I figured out rB(2i,-1j,0), rc(2i,1j,0),rd(1i,0,2k) can you check if my vectors r right. After find the vectors of point B,C,D I calculated the unit vector, not I am...
  25. M

    Finding the Coefficient of Friction for a Homogeneous Cube in Static Equilibrium

    Homework Statement Homogeneous cube with one edge lying on the floor and the other on a smooth vertical wall. The underside of cube with a horizontal surface makes angle of \frac{\pi}{6}.What is the value to the coefficient of friction between the cube and the floor to cube remain in...
  26. B

    Statics: a hinge held up by a string with a mass

    Homework Statement A uniform beam of mass M and length L is mounted on a hinge at a wall as shown in the figure. It is held in a horizontal position by a wire making an angle (theta) as shown. A mass m is placed on the beam a distance from the wall, and this distance can be varied...
  27. H

    Mechanics statics couple moment problem

    Homework Statement Find the force 'p' and angle 'alpha'. Homework Equations m=rXf The Attempt at a Solution I calculated the couple moment by using M=rXf, I plugged r=12 and f=8 and the answer come out to be 96 lb.m. After finding the couple moment I am stuck now, I could not...
  28. Femme_physics

    Suspension cable statics calculus problem

    Homework Statement http://img706.imageshack.us/img706/7156/mecx1jpg.jpg Homework Equations http://img837.imageshack.us/img837/6987/equationsr.jpg The Attempt at a Solution I find myself with 2 unknowns, 1 equation. http://img708.imageshack.us/img708/4281/mecx2.jpg
  29. Femme_physics

    Statics Mechanics: Looking for the flaw in my logic

    Yep...back to old statics. Not because I have a test (already passed it in flying colours) just for fun seeing what I can solve and can't...now I ran into this:Homework Statement http://img705.imageshack.us/img705/1533/pulleyf.jpg Statics: The weight is 50kg. Find force P to hold it in...
  30. S

    Where Can I Find a Summer Statics Class for My ChemE Student?

    Hello, I am the parent of a ChemE student. He is a Jr at a California State University. He has some learning difficulties which makes problem solving / life issues a bit tough on him. I am just trying to help him out. He failed Statics last fall. He just came home from Spring Break and...
  31. J

    Need Information about statics class offered online?

    URGENT need Information about statics class offered online?? I need to find a university or comm. college that will be offering statics online over the summer. If you have any ideas of schools i could call please list them. Thanks!
  32. J

    What Is the Maximum Mass That Keeps Truss Forces Within Limits?

    Homework Statement Determine the largest mass m of the suspended block so that the force in any member does not exceed 52 kN(T) or 47 kN(C). Homework Equations ƩM = 0 ƩFy = 0 ƩFx=0 The Attempt at a Solution Did I assume the arrows right? Would this be the right track to...
  33. G

    Statics: System (3D) in equilibrium - determine unknown variables (h)

    Homework Statement Good day to all. I have been given a problem in statics and a system in equilibrium which in turn is giving me some problems. I have attached in a pdf file the problem context as well as my attempt at a solution. I have done so, because I was experience some problems with...
  34. G

    Statics: System in equilibrium - determine height (h)

    Homework Statement Good day to all, I have been given a problem in statics, ore specifically a system that is in equilibrium, but a system I am having some trouble with. I have attached (in pdf) the problem's context and the free body diagram I have drawn. The data we are give are as...
  35. Femme_physics

    Basic Statics - A weird outcome. Contradictory?

    This is not a HW question! THIS IS A DISCOVERY that I want to explore. I will explain it as follows: Suppose I have this exercise, where I know the static coeffecient between the beam and the floor is 0.3, whereas in the wall there is no friction. I want to find out if the beam slides, or...
  36. U

    Fluid statics with Pascal's barrel

    I am confused about the some of the concepts behind fluid statics. Here is an example to illustrate this, using Pascal's barrel experiment. Consider a cylindrical barrel with cross-sectional area A and height H. Now insert a straw of height h and cross-sectional area a so that the total of...
  37. N

    Moments about a point (statics)

    Homework Statement Homework Equations M = F*r The Attempt at a Solution I tried splitting each force into its xy components and solve but the answer is wrong. Here is my attempt: For point A: Horizontal moments: (3 * cos 25) * 5.4 - (2 * cos 30) * 4 Vertical moments: - 4 * 1.5 - (3...
  38. T

    Statics problem, determinate without moments, indeterminate with?

    Hey everyone. First time poster here. I was helping a friend do some Statics homework (I completed the course last Fall), and I ran into a really unsettling problem. I have done this problem over several times with the same result. When I do the problem only summing forces in the X and then Y...
  39. M

    What is the support reaction at E for the 9m length beam?

    Calculate the support reactions at B and E for the 9m length beam shown below. I have the answers at 4.71KN and 1.79KN but it is old work that i am revising and i can't remember how i got to them. One of the supports not being at the end is throwing me off. If anyone could show a rough working...
  40. A

    U-Tube Fluid Statics: Solving for Water Column Length and Mercury Rise

    Homework Statement Mercury is poured into a U-tube. The left arm has a cross-sectional area A1=.001 m and the right has A2=.0005m. One hundred grams of water are then poured into the right arm. Determine the length of the water column in the right arm of the U-tube; given the density of...
  41. G

    Help with Statics and Strengths of Materials

    Hi, I just signed up with the forum. I have a degree in Mechanical Design, have been working as a drafter. It's been about 10 years since I've done any statics and wanted to re-learn this stuff by making a bucket loader for my garden tractor. The last few months I've been reading my...
  42. T

    2d statics truss, joint method

    Homework Statement Determine force of each member using joint method Homework Equations T = F x D The Attempt at a Solution Answers are: Fab 2465 T Fbd 1200 T Fbc 1375 C Fdc 750 C Fde 860 T (This one is what I tried) Fce 649 C Fac 1922 C Thanks.
  43. B

    Statics in traingles, or trusses

    Hi there, I have been given the questions below as part of some revision before we begin mechanics next term. I have looked back through my notes and I seem to be missing the notes on calculating the forces. So far I know XZ = 9.49m ZY = 4.24 Angle x = 18.4 Angle y = 45 Angle Z =...
  44. P

    Statics Question (Using Modulus of Rigidity)

    Homework Statement Find the displacement (mm) in the horizontal direction of point A due to the force, P. P=100kN w1=19mm w2=15mm Homework Equations \tau = G * \gamma \tau = Shear stress = P / A \gamma = Shear strain = (pi / 2) - \alpha The Attempt at a Solution I haven't...
  45. H

    Calculating Equivalent Forces in Statics

    Homework Statement Replace the force for by the equivalent of two forces parallel at the dot and the other perpendicular to the beam. The force P is 2000 N Determine the forces!Homework Equations Fx= P*cos(x) = Fy= P*sin(x) = The Attempt at a Solution Fx= 2000 N* cos(75)= 0.517 kN Fy=...
  46. K

    Statics Homework Problem: Solving Forces Using Sin Law

    Homework Statement http://img843.imageshack.us/img843/5370/helpxd.jpg Homework Equations Sin law The Attempt at a Solution I got to: F1/sin(105) = F1u/sin(45) = F1v/sin(30) I get F1u = - 219 and F1v = 254.5... It says it is wrong, not sure what I did.
  47. P

    Statics - Mechanics of Materials, check my work please?

    Could someone please check this for me? I attached a rough free body diagram of the whole frame. Any help is appreciated. Homework Statement The member ACF of the frame loaded as shown is connected to member BCD by means of a smooth peg and slot C with force P = 930 N at point D...
  48. K

    Statics problem - bridge made of 2 segments

    ƩHomework Statement Bridge consist of two identical segments M and N connected by rods as shown in the picture. Each rod makes angle of 45° with the horizontal line. Determine the axial forces in each rod due to the load P at point G. http://img266.imageshack.us/img266/2156/62688168.th.jpg...
  49. M

    How Is the Right Triangle Used in Truss Force Calculations?

    Hi, I have a, I believe simple, problem. I am studying for a Statics final and while doing problems with a Truss I came to a problem that I did not know how to solve. It is already solved for me, but I do not get how. The truss has a force coming out from the side but instead of an angle there...
  50. K

    Is my solution to this statics problem correct?

    Hi PF I have a statics problem that i solve. BUT I’m insecure rather or not it is solved correctly. The mechanical system is shown in the link below http://peecee.dk/upload/view/340798 A weight less wire is supsended from the wall in point C and attached to a heavy bar at point A. The...
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