Page 1 :
J, "------ ------ ------, , (, , GENERA L SCIENCE, I PHYSICSj, , FORCE AND PRESSURE, FORCE, Force 1s the cause which provides motion, to the stationary body or stops the moving, body or changes the velocity of the body., If we kick a football. then it starts moving, in a definite direction, we could have kicked, in some other direction also. This means that, force is a uector quantity. A cricket ball is hit, of a bat to deflect in desired direction. We, apply force by bat on ball in a certain direc-, , Consider a moving car or a cydc on a, plane road. There are four forces acting on, t hem. One is th e weight of the vehicle acting, down and second one is the reaction force of, the ground, acting invertically upward.direction. Third force is what is applied by us to, move the vehicle and the fourth one is the, friction of the surface of the road, which acts, in a direction opposite to the direction of m<r, tion of vehicle., , Definition : Force is that physical cause, which changes the state of rest or state of motion, ofa body. It either changes or tries to change the, shape of bodies., Force is a vector quantity. It _h as both, magnitude and the direction. The SI unit of, force is newton. The symbol of which is N. The, forces acting on a body can behave in two, ways: (iJ Balanced force or (ii) Unbalanced, force., , Balanced Force, If a force is applied toward~ right hand,, the block starts moving in the n ght hand . If, 0 n the other hand a force is applied on left, hand side the block starts moving towards, lt:ft hand. 'u equal force is applied from both, side in apposite direction, the block docs not, move. This means that the total effec~ of the, forces is neutralized , then forces are swd to be, balanced., If the resultant force of several forces ac•, ting on a body is zero then the forces are called, balanced force ., llnbalanced Foree, If several forces are worhing on a body, and their resultant is not zero, then these are, Called un balanced forces., , o naloru, Fricti~, ---+, Dircct(on of, , ~, , i, , l Q, , l, , Wo1ghtofCar, , i, , for-:, , R~, , . ,, Reaction ,orcc, , con., , applied, Fonx, lom~c, , ~, , FnC'-011~, , CffW>OJ«, Fam: r·, 1, i:,cwa., ~, , "~, :, ~, Du-.cr,on, , _ _ _ ofmouoc, , ~, , -, , l, , 'l'"t:ch:ofC}.:l:, , Reaction force is just balanced by weight, of the vehicle. Frictional forces has a limiting, value. If the force applied is less, then force uf, friction just balances the applied force . All the, forces are balanced and the vehicle does not, move. But if we apply greater force to move, the vehicle, frictional force does not increase, beyond a certain value and so the applied, force being larger, forces are unbalanced. So, the vehicle move in the direction of applied, force., If the peddnlli ng of bicycle is stopped, it, stops as th e forces are balanced, the frictional, force gradually retard it and finally 1t stops., lftho person holding the suitcase loaves it, the, upward force is cut and tt fnlls., Galileo, told that if balanced forces ore, applied on any body or no force is applied, if it, ts stationary, it will rem ain stationary, if it is, unzfonnly mouing, it will continue to m oue, uniformly in the same straigh t line.

Page 2 :
NEWTON'S LA\VS OF MOTION, To describe the motion of t he moving, objects Newton gave three luws of motion :, (l) Newton's First Law of Motion, Every body in this universe will continue, in its state of rest or uniform ntotion in a, straight line unless acted upon by some external force., The first part of the law is obvious. If we, observe that s·o me object is stationary with, respect to us, it remains stationary if not, disturbed. It cannot move by its own. This, state of the body is called the state of rest., If we kick a football, i t starts moving in, some dir~ction, rolls on the ground for sometime then stops. If we stop pedalling our, bicycle, it stops after some time. Aristotle, believed that force is necessary to keep the ·, body moving uniformly. A rolling ball stops ., because of frictional force present. Similarly, a bicycle stops if pedalling is stoped. Galileo, and thereafter Newton told ,. that no force is·, required to keep a body in a uniform motion, along a straight line if no other force such as, friction etc. are present. The second part of the, above law is, Every body in this \universe will continue in, its state of unifonn motion in a straight line,, unless acted upon by some external force. ·, Inertia, From Newton's first law it can be safely, concluded that "a body will change its state of, rest or state of uniform motion only when some, external force acts on it." In other wo'f ds, any, thing or material is incapable of chan&ing its, state of rest or state of uniform motion, and, hence is in the state of inertness or inertia., Law of inertia : The tendency of a body, to continue in its state of rest or uniform motion in a straight line is called its inertia., Inertia can be further divided into two, types:, (1) Inertia of Rest : The tendency of a body, , to continue in its state of rest and oppose any, change when an exrernal force is applied is, called inertia of rest., . In order to produce change in lighter, bodies smaller force is sufficient but for, heavier bodies larger force is required to, , change i'L H stale. The mass of the body i 8, , -, , meatJ ure of its inertia., a, JJ)xample of Inertia of Rest :, The pu~senger sitting jn a bus falls back., ward when the bus suddenly starts. The, reason is that when the bus moves, the Pas., senger due to the property of inertia of rest, ate left behind and hence fall backwards. ', (2) Inertia af Motion : The tendency of a, body to continue in its state of motion is called, ine;rtia of motion., Examples of Inertia of Motion :, A rider falls forwards when a galloping, horse stop~ suddenly. When the horse stops., the rider on account of inertia of motion, continues moving and hence falls in forward, direction., The property offorce that a body possesses, due to the ·c ombined effect of its mass and, velocity is called momentum., Or, Momentum is defined as the force possessed _by a body. at some particular instant, dur:1ng its course of motion. Mathematically., it is the pr<:>dtict of mass and velocity., :. Momentum =·Mass-x Velocity, p=mx v, where p is momentum, m mass and v, velocity of the body., Momentum is a vector quantity . The SI, u11:it of momentum is kg ms-1., Law of Conservation of Momentum : It, states that the total momentum of a systetU, remaining constant, if no external force is, acting on the system., (2) Newton's Second Law of Motion, The law states that the rate .of change of, momentum of a body is directly proporti~71 al, to the impressed force and takes place in, direction in which the force acts., 1, Expression of force: Let a body ofmass", move with an initial velocity u such that a~er, a time period oft second it acquires a velocitY, v under the action of a force F. Then, Initial momentum of the _body = mu, Final momentum of the body == mv, Change in momentum int second, =mv-mu, , °