Analyzing

Physics Form 4

Forces in Equilibrium

. remains stationary (if the object is stationary) • (ii) moves at a

constant velocity ( if the object is moving)

• The principle of the forces in equilibrium states,

• “When forces act upon an object , the object is said to be in a state of equilibrium when the resulting force acting on the object is zero (no net force acting upon it) ”

Examples Forces in Equilibrium

Weight = Normal reaction Buoyant force = Weight

Weight = TensionWeight = Normal reaction

Examples Forces in Equilibrium

Weight = Normal reaction

Pulling force = Frictional force

Weight = Lifting force

Driving force = Dragging force

Resultant force

Force is a vector quantity and hence it has magnitude and direction.Two or more forces which act on an object can be combined into a single force called the resultant force.If two forces are in same line, we simply add the forces if both pull or push together; subtract them if one is in the opposite direction

Two Forces in Equilibrium

P + Q = 0 P = - Q

Three Forces in Equilibrium

P

Q

R

3 forces in balance

Triangle method

Refer example 2 module

Parallelogram method Two forces of 40N and 60 N act at 600 to each other at a point as represented below

1. Choose a scale

Suppose we let 2cm represent 10N. Then an 8cm line represents the 40N force and a 12cm line represents the 60N force. Draw these lines with a 600 angle between them:

2. Complete the parallelogram

3. Draw the diagonal from the point of application of the forces

The diagonal labelled R represents the resultant force - measure this and convert its length to newtons:Diagonal R = 17.4cm, so the resultant force R = (17.4/2)*10 = 87N4. Measure a suitable angle:The angle A = 230.Thus, the resultant of the two original forces is a force of size 87N acting at 230 to the 60N force

Resolution of forces

Fx = F cos Fy = F sin

A force can be resolved into two components, that is, (i) the horizontal component, Fx and (ii) the vertical component , Fy

• is an angle between the force F to the horizontal line•the sign of the force depend on the quadrant where the force , F is placed

Inclined plane

A = W sin

B = W cos

exampleFind the values of Px and Py for the following figures.

Figure shows a stationary wooden block of mass 50 g which is placed on a inclined plane that is at an angle of 40o to the horizontal. What is the magnitude of the weight parallel to the inclined plane