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FORCEFORCE

BYDR AJAY KUMAR

DAVV INDORE

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Meaning& Nature of ForceMeaning& Nature of Force

• Force produces motion , stops motion and prevent motion.

• It may increase speed decrease speed or cause object to change direction.

• Force may be a pull or push to cause a motion or balance each other so that body remain stationary.

• Force is the effect that one body produces on another

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Meaning& Nature of ForceMeaning& Nature of Force

• How a force affects a body is determined by

1. the size or magnitude of the force

2. the direction in which the force is acting

3. the exact point at which the force is applied to the object

Note: A change in any one of the above alters the nature of motion.

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ExampleExample

• Two forces acting in the same line with the center of an object will produce linear motion.

• The same force also applied in the same direction but off center will cause a rotatory motion.

• No motion will occur if these forces are applied at the same point but in opposite direction.

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• Because force has both the magnitude and direction it is a vector quantity.

• Graphically the magnitude of the force is represented by length of the vector line.

• The force is always represented by a pull away from the point of application.

• The force vector may also be resolved and combined using a trigonometric relationship.

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Sources of ForceSources of Force

• The action of a force may be internal or external.

• Internal forces are defined as forces that are generated within a system or body. (Internal forces are unable to move the bodies C.G. without the ability to act upon outside masses or body.) Ex: Muscular Force

• External forces are forces that are outside a body but can act upon that body. (external forces enable a body’s C.G. to be moved.)Ex: Gravity, Air / Water Resistance

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Unit of ForcesUnit of Forces

• Newton : A Newton is that amount of force which is required to accelerate a mass of one kg at the rate of one mts/ sec².

• Pound : A pound is that amount of force which is required to accelerate a mass of one slug at the rate of one foot / sec².

• Dyne : A dyne is that amount of force which is required to accelerate a mass of one gram at the rate of one cm / sec².

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Aspect/Properties of ForceAspect/Properties of Force

• Magnitude : The quantity of force.• Direction : The direction of a force is along

its action line. Because the force of gravity pulls all objects towards the earth’s center, the direction of gravitational force is vertically downward.

• Point of Application : The point of application of a force is that point at which the force is applied to an object. In the case of gravity this point is always object C.G.

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• Component of Force : A force may be resolved into a vertical and a horizontal component, and the relative size of these components depends upon the angle at which the force is applied.

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Parallelogram Law of ForceParallelogram Law of Force

• If two forces acting at a point at any angle at each other they are represented by the two adjecent side of a parallelogram in magnitude as well as in direction and their resultant will be = the diagonal passing through that point.

• The length of the diagonal will give us the magnitude of the resultant and the angle made by any of these two forces will give us the direction.

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ParallelogramParallelogram

P

P

Q Qθ

θά

O

Y

M

Z

X

Q Sin θ

Q Cos θ

R

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• R = ⌡P2 + Q2 +2PQ. Cosθ

• Tan α = Q Sinθ

• P + Q Cos θ