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