Equilibrium class 9 | conditions of equilibrium class 9 | 9th class physics | atifahmedofficial скачать в хорошем качестве

Equilibrium class 9 | conditions of equilibrium class 9 | 9th class physics | atifahmedofficial

Equilibrium class 9 | conditions of equilibrium class 9 | 9th class physics | atifahmedofficial 4.8 EQUILIBRIUM Newton's first law of motion tells us that a body continues its state of rest or of uniform motion in a straight line if no resultant or net force acts on it. For example, a book lying on a table or a picture hanging on a wall, are at rest. The weight of the book acting downward is balanced by the upward reaction of the table. Consider a log of wood of weight w supported by ropes as shown in figure 4.26. Here the weight w is balanced by the forces F1 and F pulling the log upward. In case of objects moving with 2 uniform velocity, the resultant force acting on them is zero. A car moving with uniform velocity on a levelled road and an aeroplane flying in the air with uniform velocity are the examples of bodies in equilibrium. A body is said to be in equilibrium if no net force acts on it. A body in equilibrium thus remains at rest or moves with uniform velocity. CONDITIONS FOR EQUILIBRIUM In the above examples, we see that a body at rest or in uniform motion is in equilibrium if the resultant force acting on it is zero. For a body in equilibrium, it must satisfy certain conditions. There are two conditions for a body to be in equilibrium. FIRST CONDITION FOR EQUILIBRIUM A body is said to satisfy first condition for equilibrium if the resultant of all the forces acting on it is zero. Let n number of forces F , F , F , 1 2 3 ...........,F n are acting on a body such that The symbol is a Greek letter called sigma used for summation. Equation 4.9 is called the first condition for The first condition for equilibrium can also be stated in terms of x and y-components of the forces acting on the body as: A book lying on a table or a picture hanging on a wall, are at rest and thus satisfy first condition for equilibrium. A paratrooper coming down with terminal velocity (constant velocity) also satisfies first condition for equilibrium and is thus in equilibrium. EXAMPLE 4.5 A block of weight 10 N is hanging through a cord as shown in figure 4.29. Find the tension in the cord. SOLUTION Weight of the block w = 10 N Tension in the cord T = ? Applying first condition for equilibrium There is no force acting along x-axis. Thus, the tension in the cord is 10 N. SECOND CONDITION FOR EQUILIBRIUM First condition for equilibrium does not ensure that a body is in equilibrium. This is clear from the following example. Consider a body pulled by the forces F1 and F2 as shown in figure 4.30(a). The two forces are equal but opposite to each other. Both are acting along the same line, hence their resultant will be zero. According to the first condition, the bod equilibrium. Now shift the location of the forces as shown in figure 4.30(b). In this situation, the body is not in equilibrium although the first condition for equilibrium is still satisfied. It is because the body has the tendency to rotate. This situation demands another condition for equilibrium in addition to the first condition for equilibrium. This is called second condition for equilibrium. According to this, a body satisfies second condition for equilibrium when the resultant torque acting Most related searches 9th class physics chapter 4 9th class physics ch 4 9th class physics 9th physics chapter 4 9th physics ch 4 9th physics physics class 9 chapter 4 physics class 9 physics 9th matric part 1 physics physics matric part 1 part 1 physics physics part 1 physics matric part 1 physics matric part 1 chapter 4 physics matric part 1 ch 4 part 1 physics part 1 physics chapter 4 9 class physics 9 class physics chapter 4 9 class physics ch 4 9 class matric part 1 part 1 matric physics sindh board kpk board punjab board all boards Karachi board by sir atif ahmad atifahmadofficial atif ahmad official #physics #class9 #9thclassphysics #9thphysics #matricpart1 #matricpart1physics #matricphysicspart1 #atifahmadofficial #sindhBoard #urdu #hindi #freeonlineclasses #onlinephysicslecture #equilibrium #conditionsofequilibrium #introductiontoequilibrium