Equilibrium of Forces

MOTION AND FORCE MOTION AND FORCE IN EQUILIBRIUMIN EQUILIBRIUM

STATIC – calculation of the forces acting on

and within structures that are in

equilibrium.

Kind of ForcesKind of Forces

• Concurrent Forces

• Non- concurrent forces

• Coplanar Forces

• Non-coplanar Forces

CONCURRENT FORCES

-forces acting at a point on a body, or whose lines of action converge at a point.

• NON- CONCURRENT

- forces acting on a body whose lines of action do not converge at point.

• COPLANAR FORCES

- forces acting on a plane

• NON-COPLANAR

- acting on more than one plane.

TYPE OF FORCESTYPE OF FORCES

• Contact Forces

• Action-at-a Distance Forces

CONTACT FORCESCONTACT FORCES

• Frictional Force

• Tensional Force

• Normal Force

• Air Resistance Force

• Applied Force

• Spring Force

ACTION-AT-A-DISTANCE FORCESACTION-AT-A-DISTANCE FORCES

• Gravitational Force

• Electrical Force

• Magnetic Force

Applied Force – applied to an object by another or by a person.

Gravity Force – force with which the earth, moon, or other massive body attracts an object towards itself.

- it is always equal to the weight of the object

Normal Force – support force - force pressing the bodies together - exerted perpendicular to the

contact surfaces. - equal to the weight of the

block

Frictional Force - opposes the motion

- proportional to the normal force

- parallel force

Air Resistance – special type of frictional force which acts upon objects as they travel through the air.

Tensional Force – force transmitted through a string, rope, or wire when it is pulled tight by forces acting at each end.

Spring Force – exerted by a compressed or stretched spring upon any object which is attached to it.

EQUILIBIRUMEQUILIBIRUM

- (latin for “equal force” or “balance”

- Is a condition of a body where it does not change its linear or rotational motion under the influence of a force or set of force.

- A body is in equilibrium when it is either at rest or moving uniformly.

A body is in equilibrium when these two conditions A body is in equilibrium when these two conditions are met:are met:

1. The vector sum of all the forces acting on it is zero.

F = 0

2. The vector sum of torques is zero.

L = 0

When a body is in equilibrium, its force diagram is closed polygon, or the sum of the rectangular components of the forces must equal zero:

Fx = 0 and Fy = 0

Free-Body DiagramsFree-Body Diagrams

Diagrams used to show the relative magnitude and direction of all forces acting upon an object in a given situation.

FREE BODY DIAGRAMFREE BODY DIAGRAM

•The only rule for drawing free-body diagrams is to depict all the forces which exist for that object in the given situation

Drawing Free-Body DiagramsDrawing Free-Body Diagrams

• Know the types of forces• Begin by using your understanding of the force types to

identify which forces are present.• Determine the direction in which each force is acting.• Finally, draw a box and add arrows for each existing

force.• Label each force arrow according to its type.

ExampleExample

• Determine the tension in each cord that supports the 200-N hanging box as shown in the figure.

45º 30º

T3 T2

T1

W=200 N

ExampleExample

• Determine the tension in each cord that supports the 150-N hanging box as shown in the figure.

35º 40º

T3 T2

T1

W=150 N

ExampleExample

• Rope 3 shown in figure below has a tension of 150 N. Determine T2 and θ1 if weight = mg = 160 N.

T3 40º Θ2 T2

T1