Force ppt class 8

full explanation of NCERT chapter of class 8 "FORCE" i hope you understand it clearly any doubts you can leave a comment i will try to reply .i have written in very simple language to make you all understand

1. FORCE AND PRESSURE
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2. Swati Mathur (Science Teacher, MLZHS, Hayathnagar) 2

3. Note: Force come in notice when at
least two bodies interact
https://youtu.be/IJWEtCRWGvI
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4. Swati Mathur (Science Teacher, MLZHS, Hayathnagar) 4

5. Force:
Force can be defined as a
push or a pull or we can say
force is a physical quantity
that can change the speed,
state, directionand
dimensionof an object.
The changes that a force can bring are………
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6. Force comes
in notice
when atleast
two bodies
interact
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7. Force can change the
state of body
Motion →Rest
Rest →Motion
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8. Force can change the dimensions of an object
i.e shape and size
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9. Force can change the direction of a moving object
https://youtu.be/B6mi1-YoRT4
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10. We have realized that, a FORCE…
Is a pull or push from one object to another.
Comes to notice when at least two bodies interact.
Is a physical quantity.
Can change speed of a moving object.
Can bring moving body to rest.
Can stop a moving object.
Can change shape or size of an object.
Can change direction of a moving object.
Therefore, none of these actions can take place without
the action of force.
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11. TYPES OF FORCES
CONTACT
FORCES
NON
CONTACT
FORCES
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13. TYPES OF CONTACT FORCES
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14. Muscularforce..
Itistheforceappliedusingpartsofthebodylikearmsorlegs.
Itisforcethatresultsduetotheactionofmuscles.
Itisacontactforce,sincethereisacontactbetweenourbodywiththeobject.
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15. ❖It is a contact force as force applied by machines in contact with another object.
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16. Frictional Force
❖Frictional force arises when only when the surfaces of two objects are in touch with
each other therefore it is a contact force.
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17. Swati Mathur (Science Teacher, MLZHS, Hayathnagar) 17

18. TYPES OF NON CONTACT FORCES
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19. Swati Mathur (Science Teacher, MLZHS, Hayathnagar) 19

20. Repulsive:
Between
same
charges
Attractive:
Between
opposite
charges
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21. Magnetic force, attraction or repulsion that arises between electrically
charged particles because of their motion.
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22. TYPES OF FORCES
https://youtu.be/iGwBZTWySWk
Types of forces
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25. PRESSURE
It is defined as “force exerted per unit area.”
•Pressure is produced when a force acts on an object.
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26. Factors on which pressure depends…
•It is directly proportional to force.p α F
•It is inversely proportional to area.P α1/A
❖Pressure is a physical quantity
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27. UNIT OF PRESSURE
S.I. unit of pressure is PASCAL (Pa)
(system Internationalis)
1 Pa = 1 Newton / 1 square meter
Pressure is defined as “1 Pascal when 1 Newton
force is applied on 1 meter square area.”
1Pa=1N/1m2
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28. Numericals
Solution:
Given: Force = 100 N, Area = 4 m
2
∴Pressure =25pa.
Example 1:
A force of 100 N is applied on an area of 4 m2.
Compute pressure being applied on the area.
Given:
Force applied by elephant F = 20,000 N, area A = 1000
cm
2
=1000/100×100m
2
= 0.1 m
2
The pressure is given by
Pressure P =F/A
=20,000N/0.1m2
= 2,00,000 N/m
2
.
Example 3:
Calculate the pressure produced by a force of 800 N acting on
an area of 2.0 m
2
.
Solution:
Pressure is defined as force per unit area or P = F / A
P = (800 N) / (2.0 m2
)
P = 400 N / m2
= 400 Pa
Example 2:
The elephant weighs 20,000 N stands on one foot of
area 1000 cm
2
. How much pressure would it exert on
the ground?
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29. 1.Calculate the pressure when the force of 200N is exerted on an area
of:
(a) 10m.square
(b) 5m.square
2.The same force F acts on four different objects having the area given
below, one by one. In which case the pressure exerted will be
maximum?
(a) 20m.sq (b) 50m.sq (c) 10m.sq (d) 100m.sq
3.A pressure of 10 Kpaacts on an area of 0.3 m.sq. The force acting on
the area will be:
(a) 3000N (b) 30N (c) 3N (d) 300N
GET THE SOLUTIONS……..
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30. We can conclude that…
•Pressureisaforceactingonanunitareaoftheobject.
•Pressureisaphysicalquantity.
•Pressuredependsupontwofactors-
1.forceapplied
2.areaoverwhichforceacts
•Whenaforceactsoveralargeareaofanobject,itproducesa
smallpressure.Butifthesameforceactsoverasmallareaofthe
object,itproducesalargepressure.
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31. •We know that pressure is inversely proportional
to area.
•Therefore more is the area, less is the pressure
exerted.
•And due to less pressure, it is more comfortable
to carry the heavyschool bag.
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32. Swati Mathur (Science Teacher, MLZHS, Hayathnagar) 32

33. Swati Mathur (Science Teacher, MLZHS, Hayathnagar) 33

34. Why it is easier to hammer sharp nail ?
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35. Why it is difficult to walk on sandy floor with pencil heels ?
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36. FLUID PRESSURE
It is defined as “pressure exerted by fluids.”
Fluid -Any material that can flow and that take
the shape of a container. (WHY?)
Example -Liquid and gas
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37. PRESSURE EXERTED BY LIQUIDS
All liquids exert pressure on the base
and walls of their containers.
Pressure exerted by liquid is:
Here,
force = weight of the liquid
Area = area of base of the vessel
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38. Pressure increases with increase in depth
•Liquid also exerts pressure on
the walls of the vessel in which
they are stored.
•The sideways pressure exerted
by liquid also increases with the
depth of the liquid.
Least depth
Least pressure
Greatest depth
Greatest pressure
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39. Liquid exerts pressure on the bottom of its container
•The pressure
exertedbyaliquid
dependsonthe
heightoftheliquid
column.
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40. Liquid exerts pressure on the walls of its container
•The sideways pressure
exerted by liquid also
increases with the
depth of the liquid.
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41. Liquid exerts equal pressure at the same depth
•Liquid also exerts
pressure on the walls of
the vessel in which they
are stored.
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42. Liquid exerts pressure in the upward direction also
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43. LIQUID EXERTS PRESSURE IN ALL DIRECTIONS
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44. We can conclude that……
•Pressure increases with increase in depth.
•Liquid exerts pressure on the bottom of its container.
•Liquid exerts pressure on the walls of its container.
•Liquid exerts equal pressure at the same depth.
•Liquid exerts pressure in the upward direction also.
•Therefore, liquid exerts pressure in all directions.
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45. PRESSURE EXERTED BY GASES
•Thepressureofagasistheforcethat
thegasexertsonthewallsofits
container.
•Airpressurearisesduetotheconstant
collisionofthetinymoleculesofthe
gasespresentintheairwiththewallsof
thecontainerinwhichitisenclosed.
•Airexertspressureinallthedirection.
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46. •Whenyoublowairintoaballoon,theballoon
expandsbecausethepressureofairmoleculesis
greaterontheinsideoftheballoonthanthe
outside.
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47. Swati Mathur (Science Teacher, MLZHS, Hayathnagar) 47

48. ATMOSPHERE (300 kilometers)
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49. ATMOSPHERIC PRESSURE
•Atmospheric pressure is due to the
weight of air present in the
atmosphere.
•Atmospheric pressure also acts in all
directions.
•Gravity pulls air molecules towards
earth.
•Creates more pressure above the
ground.
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50. Why do climbers take oxygen
cylinder along while climbing
height ?
•Mountaineerscarryanoxygencylinder
alongwiththem.
•Itisbecausewhentheyclimbmountains,
asaltitudeincreases,theamount
ofoxygenlevelintheatmosphericair
decreasesastreesarenotfoundat
higheraltitudes.
•Asaresult,mountaineerssufferfrom
dizziness.
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51. Why deep sea divers wear special suits
while diving ?
•Liquidpressureincreaseswithdepth.
•Thedivingsuitsarerequiredto
enablediverwithstandthesepressures
andswimcomfortably.
•Hence,Deepseadiverswearspecially
designedsuitstoprotectthemselves
fromhighpressures
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52. TO SHOW EXISTENCE OF ATMOSPHERIC PRESSURE
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53. Magdeburg hemispheres to show large atmospheric pressure
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54. OUR BODY AND ATMOSPHERIC PRESSURE
If the pressure due to atmosphere is so great then why we are not
crushed by it ??
Our bodyhave an internal bloodpressurewhich is more or less equal
to theatmospheric pressureinoursurroundings. Thus the
twopressurecancel each other and that is howour body balance with
atmospheric pressure.
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59. We can conclude that….
•Airexertspressureinallthedirection.
•Atmosphericpressureisduetotheweightofair
presentintheatmosphere.
•Gravitypullsairmoleculestowardsearth.
•Atmosphericpressuredecreaseswiththehigh
altitudes.
•Ourbodyhaveaninternalbloodpressurewhichis
moreorlessequaltotheatmospheric
pressureinoursurroundings.
•Vacuumisaspacecontainingverylittleornomatter.
•Avacuumcanbecreatedbyremovingairfroma
space.
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60. A barometer is a scientific instrument that is used to measure air
pressure in a certain environment.
Pressure tendency can forecast short term changes in the weather.
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