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Chapter – 11
Force and Pressure
Force: A push ora pull, thatchanges or tendsto change thestate of restor of uniform motion of anobject or changes its direction orshape. A force arises due to theinteraction between twoobjects. Force hasmagnitude as wellas direction. TheSI unit offorce is newton. A change inthe speed ofan object orthe direction ofits motion orboth implies achange in itsstate of motion. Force acting on an object may cause achange in itsstate of motion or a change in its shape. A force canact on anobject with orwithout being incontact with it.
Types ofForces:
Contact Forces: The forces act ona body whenthe source offorce is inactual contact with the body. The point where the force is applied on an object is called the point of application of force (or point ofcontact).
(i) Muscular Force: The force exerted by the muscles of the body. We make use of muscular force of animals like bullocks, horses and camels to get ouractivities done.
(ii) Mechanical Force: The force produced by amachine.
(iii) Frictional Force: The force thatopposes the motion of an object.
Non-Contact Forces: Forces which do not involve physical contact between two bodies onwhich they act.
(i) Magnetic Force: A magnet exerts a non-contact forceon objects madeof iron, steel, cobalt or nickel.
(ii) Electrostatic Force: The force which result due to repulsion of similar charges or attraction ofopposite charges.
(iii) GravitationalForces: The forcethat exists between any two bodies by virtue of their mass.
Pressure:
Thrust acting per unit surface area is called pressure. Thrust is the force acting on an object perpendicular to itssurface. In SIsystem, pressure ismeasured in newton per square metre which is equal to 1 pascal (Pa). Like solids, fluids (liquids and gases) also exert pressure. A solid exerts pressure only in the downward direction due its weight, whereas liquids andgases exert pressure in all directions. Hence liquids and gases exert pressure on the walls of their container. The thick blanket of air that covers the earth is termed atmosphere. The pressure exerted by the atmosphere is called atmospheric pressure. The tremendous atmospheric pressure surrounding us isnot felt byus because thefluid pressure inside our bodies counter-balances the atmospheric pressure around us.
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