Class-8 ppt for ch- force and pressure

1. ARSHPREET KAUR
CLASS-8 D
ROLL NO-8

4. UNDERSTANDING PRESSURE
 Pressure ,P as force unit area
STATE RELATIONSHIP BETWEEN PRESSURE AND AREA
 Pressure depends on 2 factors :
a. Forces acting
b. Area of surface
 Pressure increases as surface area decreases

5. APPLICATION INVOLVING IN HIGH PRESSURE
A sharp knife has very small surface area
on its cutting edge so that high pressure can
be exerted to cut the vegetable.
In the case of blunt knife ,the cutting edge BLUNT KNIFE
is thicker ,as the result, the force of our
hand falls over a larger area of the knife,
producing less pressure.
HENCE IT IS DIFFICULT TO CUT WITH BLUNT
KNIFE SHARP KNIFE

6. NAILS,NEEDLES AND PINS
Nails , needles and pins have very sharp
ends with very small surface areas. when
a force is applied to the head of the nail,
the pressure will drive its sharp end into a
piece of wood easily.

7. FOOTBALL BOOTS
 the stud on football boots have
only a small area of contact with the
ground . The pressure under the
studs is high enough for them to sink
into the ground , which gives extra
grip.

8. APPLICATION INVOLVING LOW PRESSURE
Skis have large area to reduce the pressure
on the snow so that they do not sink in too far.

9. TRACTORS
A tractor moving on soft ground was
wide tires to reduce the pressure on
the ground so that they will not sink
into the ground .

10. BAGS
A wide shoulder pad of a heavy
bag will reduce the pressure
exerted on the shoulder of a
person carrying a bag.

11. UNDERSTANDING PRESSURE IN LIQUID
Liquid with higher density exerts a
higher pressure.
This is because liquids with higher
density has a larger weight.
The pressure in a liquid is directly
proportional to the density of the
liquid .

12. CHARACTERSTICS OF PRESSURE IN LIQUIDS
Pressure increase with depth.
Pressure acts in all direction.
Pressure at 2 points at the same
liquid are equal .
Pressure doesn’t depend on area
of surface.
Pressure doesn’t depend on shape
or size of container.

13. APPLICATION OF ATMOSPHERIC PRESSURE
DRINKING STRAW
When sucked, air inside straw is removed,
Leaving a low pressure area.
The higher atmospheric pressure acts on
The surface of water and pushed drinks
Into the straw.

14. SUCKER HOOK
When the sucker hook is press, the air
inside is pressed out and leaving a low
pressure area.
The higher external atmospheric
pressure outside pressed down on the
hook and makes it stick firmly to the
wall.

19. CONTACT FORCES
Contact forces are those types of forces which result
when two interacting objects are perceived to be
physically contacting each other.

20. TYPES OF CONTACT FORCES
MUSCULAR FORCE
FRICTIONAL FORCE

21. MUSCULAR FORCE
Muscular strength is defined as
the ability of a muscle group to
develop maximal contractile force
against a resistance in a single
contraction. Muscular endurance
is the ability of a muscle group to
exert sub maximal force for extended
periods.

22. FRICTIONAL FORCE
Force that opposes the motion
of an object . It always acts in the
opposite direction to the attempted
motion. Its size depends on how
rough the surface is and on the
weight pushing down on the surface.

23. NON CONTACT FORCES
GRAVITATIONAL FORCE
MAGNETIC FORCE
ELECTRIC FORCE

24. GRAVITATIONAL FORCE
The force of attraction
between two objects due to
their masses.

25. MAGNETIC FORCE
The force of attraction
between a magnet and
another suitable object
or magnet.

26. ELECTRIC FORCE
Force exerted by a charged
body by another charged
body.