ICSE Class 8 Physics Notes Chapter 3 Force and Pressure

ICSE Physics Class 8 Notes Chapter 3 Force and Pressure

→ FORCE : “Is the cause which changes the state of a body (rest or state of motion) or it changes the size or shape of a body”.

Weight of a body → The force with which a body is attracted towards the centre of earth mg = force of gravity.

→ A force does not change the mass of the body that is why mass of a body on earth and moon in same but weight → force exerted on body is different.

→ Force cannot be seen but it is felt.

→ represents force, length of arrow gives magnitude and arrow points the direction.

→ S.I. unit of force is Newton (N).

→ Newton : “Is that much force, which when acting on a body of mass 1 kg produces in it (increases) a speed of 1 m
s^-2 in the direction of its motion. kgf = 9.8 N = 10 N (nearly)

→ RIGID body : “When a force is applied on a body and inter¬spacing between its constituent particles do not change is called RIGID body” force can cause only the motion in it.

→ NON-RIGID body : “When force applied changes inter-spacing.” Force causes both change in its size (shape) and the motion in body.

→ TURNING EFFECT : “When force is applied on a pivoted (at a point) body, it can turn it and turning of body about point of rotation is called TURNING EFFECT.” or Moment of force. This is measured as:

→ TURNING EFFECT = MOMENT OF FORCE = Force x perpendicular distance from point of rotation.

Moment of force = F x OP
S.I. unit of moment of force – N x m = Nm

→ THRUST : “Force acting normally on a surface.” Smaller the area of surface, larger is thrust.

→ PRESSURE : “Thrust per unit area.” S.I. unit of pressure is Nm^-2 or pascal (Pa)

→ If Thrust is measured in kgf and area in cm , then pressure is expressed as kgf cm^-2.
ATMOSPHERIC Pressure: 1 atm = 76 cm of mercury column 1 atm = 1.013 x 10⁵ Pa

→ FACTORS AFFECTING THE PRESSURE :  {∵ P = \(\frac {F}{A}\)}

1. Area: Greater the area, lesser is pressure and lesser area, greater is pressure.
2. Magnitude of thrust acting: greater thrust, greater pressure.

→ Factors Affecting LIQUID PRESSURE = hdg

1. High of liquid column: increases with height
2. Density of liquid: increases with density of liquid.
3. Gravity …………… constant.

→ ATMOSPHERIC PRESSURE: “Pressure exerted by the air of atmosphere around us.”

→ STANDARD ATMOSPHERIC PRESSURE 1 Atm = 76 cm ofHg column = 1.013 x 10⁵ Pa

ICSE Class 8 Physics Notes