9th

Govt. Sen. Sec. School, Samana (Patiala)

Submitted By: Class 9th (Kiran Kalyaan) (Karan Kumar)

Supported By: Sh. Satpal Verma S. Rashpal Singh (Science Master)

Computer Support Smt. Monika Bansal, Sh. Sonu Bansal (Computer Teachers)

INTRODUCTION When we want to open a door we have to push the door handle. When we want to close the door we have to pull the door handle with our hand. This means that to move a body, it has either to be pushed or pulled. A push or pull on body is called force. In physics, force is an influence that may cause a body to accelerate. It may be experienced as a lift, a push, or a pull, and has a magnitude and a direction. The actual acceleration of the body is determined by the vector sum of all forces acting on it (known as net force or resultant force). In an extended body, it may also cause rotation or deformation of the body. Rotational effects and deformation are determined respectively by the torques and stresses that the forces create. Force is a vector quantity defined as the rate of change of the momentum of the body that would be induced by that force acting alone. Since momentum is a vector, the force has a direction associated with it.

HISTORY 1. Force was first described by Archimedes. 2. Galileo Galilei used rolling balls to disprove the Aristotelian theory of motion (1602- 1607) 3. Isaac Newton is credited for giving the first mathematical definition of force. However, he understood that the definition is not physical correct. 4. Charles Coulomb is credited for experimental discovery of the inverse square law of interaction between electric charges using torsion balance (1784). 5. Henry Cavendish’s in

measured the force of gravity

between 1798 two masses (in torsion balance experiment)

With the development of quantum field theory and general relativity in 20th century it was realised that “force” is strictly a concept which arises from each theory in a totally different way and in both theories, it is only a helping concept which cannot be physically correct. In QFT, the force is arising from conservation of momentum of interacting elementary particles. Aristotle and others believed that it was the natural state of objects on Earth to be motionless, and that they tended toward that state (eventually settling down to inertness), if left alone. This was a common experience of humans with ordinary conditions in which friction was involved, so Newton's idea that force naturally produces a constant increase in velocity was not an obvious one. Frictional forces, acting in opposition to other kinds of forces, historically tended to hide the correct mathematical relationship between simple unopposed force and motion.

DEFINITION A force is an influence which tends to set a stationery body in motion or stop a moving body or which tends to change the speed and direction of a moving body, or which tends to change the shape of a body.

EFFECTS OF FORCE A force can produce the following effects: • A force can move a stationery object. • A force can stop a moving body. • A force can change the speed of a moving body. • A force can change the direction of moving body. • A force can change the shape & size of a body.

Types of Force Force is of two types: 3. Balanced Force 4. Unbalanced Force

Balanced Force If the resultant of all the forces acting on a body is zero, the forces are called balanced forces.

Unbalanced Forces If the resultant of all the forces acting on a body is not zero, the forces are unbalanced forces.

Laws of Motion 2. A body at rest will remain at rest and a body in motion will continue in motion in strait line with the uniform speed unless it is compelled by an external force to change its state of rest or of uniform motion 3. The rate of change of momentum of a body is directly proportional to the applied force, and takes place in the direction in which the force acts. 4. To every action there is an equal and opposite reaction.

Units The SI unit of force is Newton which is denoted by N. A Newton is that force which when action on a body of mass one Kg produces an acceleration of 1m/s2 in it. Formula : Force = Mass * Acceleration F=M*A

Conversions Below are several conversion factors between various measurements of force: 1 dyne = 10-5 newtons

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1 kgf (kilopond kp) = 9.80665 newtons

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1Metric Slug = 9.80665 kg

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1 lbf = 32.174 Poundals

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1 slug = 32.174 lb

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1 kgf = 2.2046 lbf

Bibliography 2. Science Book of Class Ninth. 3. Microsoft Encarta 4. Internet