1. MOMENT OF FORCE Dr. Ajay Kumar School of Physical Education DAVV Indore

2. Introduction and concept In addition to linear forces in which all forces occurs along the same action line, In addition to linear forces in which all forces occurs along the same action line, Or Or The concurrent force in which force acting at different angles are applied at the same point. The concurrent force in which force acting at different angles are applied at the same point. Another situation exist in which force not act in the same action line but parallel to each other act at different points on a body. Another situation exist in which force not act in the same action line but parallel to each other act at different points on a body. These forces are known as parallel forces. These forces are known as parallel forces.

3. Cont. The effects of parallel forces on a body depends on the magnitude, the direction, and application point of each other. The effects of parallel forces on a body depends on the magnitude, the direction, and application point of each other. Parallel forces may act in the same or opposite direction. Parallel forces may act in the same or opposite direction. They may be balanced and cause no motion or They may be balanced and cause no motion or They may cause linear or rotatory motion. They may cause linear or rotatory motion.

4. Cont. If we exert equal and opposite forces rotatory motion about the center of gravity of the weight will occur. If we exert equal and opposite forces rotatory motion about the center of gravity of the weight will occur. The effect of equal parralel force acting in opposite direction is called a couple or force couple. The effect of equal parralel force acting in opposite direction is called a couple or force couple. Example : Steering of the if controlled by both hands. Example : Steering of the if controlled by both hands.

5. Cont. The turning effect of a force is called torque or moment of force. The turning effect of a force is called torque or moment of force. The torque about any point equals the product of the force magnitude and its perpendicular distance from point of application of force to the point of axis of rotation. The torque about any point equals the product of the force magnitude and its perpendicular distance from point of application of force to the point of axis of rotation.

6. Cont. The perpendicular distance is called the moment arm or torque arm. The perpendicular distance is called the moment arm or torque arm. Since a force moment is the product of force and moment arm length, it may be increased or decreased by increasing or decreasing either the force or the force arm length. Since a force moment is the product of force and moment arm length, it may be increased or decreased by increasing or decreasing either the force or the force arm length.

7. Cont. In human body the mass or weight of a segment cannot be altered, therefore the torque of a segment due to gravitational force can only be changed by changing the length of the momnet arm in relation to the axis. In human body the mass or weight of a segment cannot be altered, therefore the torque of a segment due to gravitational force can only be changed by changing the length of the momnet arm in relation to the axis.

8. Moment of Inertia The quality of a body to resist change in its state of motion or rest was identified as inertia. The quality of a body to resist change in its state of motion or rest was identified as inertia. The inertia of a body with respect to the linear motion was shown to be directly proportional to the mass of the object. The inertia of a body with respect to the linear motion was shown to be directly proportional to the mass of the object. The heavier the object the more force it takes to start it moving and more force to stop it. The heavier the object the more force it takes to start it moving and more force to stop it.

9. Cont. This is also true in rotatory motion. This is also true in rotatory motion. The amount of force needed to start or stop a spinning object is related to its mass. The amount of force needed to start or stop a spinning object is related to its mass. But practically we can easily feel that to start a hammer moving in a circular motion or to stop a moving hammer in a circular fashion is difficult. But practically we can easily feel that to start a hammer moving in a circular motion or to stop a moving hammer in a circular fashion is difficult.

10. Cont. Therefore it seem that hammer inertia is greater when moving in an angular pattern than moving in a linear path. Therefore it seem that hammer inertia is greater when moving in an angular pattern than moving in a linear path. Since the mass of the hammer does not change, this increase in inertia must be due to some other factor. Since the mass of the hammer does not change, this increase in inertia must be due to some other factor.

11. Cont. In the same way the torque causing rotatory motion is dependent upon the magnitude of the force and the perpendicular distance from the line of action to the force to the axis, the inertia of a rotatory body is affected by the distance between the mass and the axis of rotation. In the same way the torque causing rotatory motion is dependent upon the magnitude of the force and the perpendicular distance from the line of action to the force to the axis, the inertia of a rotatory body is affected by the distance between the mass and the axis of rotation.

12. Cont. As the distance between the axis and the mass increases, the inertia increases. As the distance between the axis and the mass increases, the inertia increases. THIS ANGULAR INERTIA IS CALLED THE MOMENT OF INERTIA (I) THIS ANGULAR INERTIA IS CALLED THE MOMENT OF INERTIA (I)

13. Cont. The exact nature of this relationship is shown in the equation for the moment of inertia The exact nature of this relationship is shown in the equation for the moment of inertia I = ∑mr 2 Where m is the mass of the object and r is the perpendicular distance between mass and axis of rotation. Where m is the mass of the object and r is the perpendicular distance between mass and axis of rotation.