Question

23. A gum bottle rests on its base. If it is placed
upside down, how does the (i) thrust, (ii) pressure
change?
26. Explain the following:
(a) Sleepers are used below the rails.
(b) A tall building has wide foundations.
27. Describe an experiment to show that a liquid
exerts pressure at the bottom of the container in
which it is kept.
28. Describe a suitable experiment to demonstrate
that a liquid exerts pressure sideways also.
29. Describe a simple experiment to show that at a
given depth, a liquid exerts same pressure in all
directions.
nrormure at a noint​

Answer 1

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-1

in the direction of its motion.

 1 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 × m=Nm

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

is thrust.

 PRESSURE : “Thrust per unit area.p = Thrust/area = F/A S.I unit of area A

pressure is Nm-2 or pascal (Pa)

 If Thrust is measured in kgf and area in Cm2

, then pressure is expressed as kgf

Cm-2

.

Answer 2

Answer:

26. A = sleeper are used below the rails because iron rails does not move and to keep it straight and the rail does not sink into the ground