Newton's First Law of Motion Video Lecture | Science Class 9

0:0:0: have you ever wondered why a car stops
0:0:2: when you apply brakes or why a ball
0:0:5: keeps rolling on a smooth surface until
0:0:7: it hits something or why a book stays on
0:0:11: a table unless you push it or pull it
0:0:14: these are some examples of how objects
0:0:16: behave when they are in different states
0:0:18: of motion or rest and the answer to
0:0:21: these questions lies in the first law of
0:0:24: motion given by one of the greatest
0:0:26: scientists of all time Sir Isaac Newton
0:0:30: Newton's first law of motion states that
0:0:32: an object at rest will remain at rest
0:0:35: and an object in motion will remain in
0:0:37: uniform motion unless acted upon by some
0:0:40: external unbalanced force an unbalanced
0:0:43: force is as the name suggests an unequal
0:0:46: Force applied on an object whereas a
0:0:48: balanced force is forces applied on an
0:0:51: object that are equal and opposite in
0:0:53: direction the first part that states
0:0:56: that an object will remain at rest seems
0:0:58: to make sense since motionless objects
0:1:1: typically don't just start moving but
0:1:4: the second part which states that an
0:1:6: object will remain in uniform motion
0:1:8: unless acted upon by external Force
0:1:10: contradicts much of our everyday
0:1:13: experience when you throw a ball it
0:1:15: doesn't keep moving
0:1:17: forever it eventually stops but where is
0:1:20: the force that stops the ball or changes
0:1:23: its state of motion our planet is a
0:1:26: puzzle of
0:1:27: forces when we move there's this sneaky
0:1:30: thing called friction that tries to slow
0:1:32: us down think of it like walking through
0:1:35: sticky mud it's tough so when we throw
0:1:40: that ball it's not that it wants to stop
0:1:42: it's just these forces like friction
0:1:44: Playing Tricks on it so in conclusion
0:1:48: all these forces act as an unbalanced
0:1:50: force that is required to change the
0:1:52: state of motion there is an important
0:1:55: word in Newton's first law of motion
0:1:57: which is uniform motion what does it
0:2:0: mean that a body will move in uniform
0:2:3: motion it means that its speed or
0:2:5: direction will not change without
0:2:7: external Force without Force there is no
0:2:11: acceleration or
0:2:13: deceleration for example you need the
0:2:15: engine to keep applying Force to
0:2:17: accelerate that is increase the speed of
0:2:19: your car or you need brakes to
0:2:22: decelerate that is decrease the speed of
0:2:24: your car in essence Newton's first law
0:2:28: teaches us how forces affect an object's
0:2:30: motion this understanding sets the stage
0:2:33: for exploring our next exciting topic
0:2:37: inertia Newton's first law of motion is
0:2:40: also called the law of
0:2:41: inertia inertia is the tendency of a
0:2:44: body to oppose any change in its state
0:2:46: of rest or uniform motion the more
0:2:50: inertia a body has the more difficult it
0:2:52: is to change its state of motion let's
0:2:56: understand this in
0:2:57: detail there are three types of inertia
0:3:0: inertia of rest inertia of motion and
0:3:3: inertia of
0:3:5: Direction let us learn about each one of
0:3:7: them in detail the inertia of rest is
0:3:11: the tendency of a body to remain at rest
0:3:13: unless an external Force acts on it for
0:3:17: example when a branch of a tree is
0:3:19: shaken vigorously ripe fruits get
0:3:21: detached and fall this is because the
0:3:25: branch comes in motion but the fruits at
0:3:27: rest tend to remain at rest due to
0:3:29: inertia of rest and get
0:3:31: detached after the fruits get detached
0:3:34: gravity plays its role in making the
0:3:36: fruits fall another example of inertia
0:3:39: of rest is when we are standing in a
0:3:41: stationary bus and the driver starts the
0:3:44: bus suddenly we get thrown backward with
0:3:47: a jerk this is because our feet are in
0:3:50: contact with the floor of the bus and
0:3:52: move along with it while the upper part
0:3:55: of our body remains at rest due to the
0:3:57: inertia of rest this creates a backward
0:4:1: force on our
0:4:2: bodies now the inertia of motion is a
0:4:5: tendency of a body to remain in uniform
0:4:8: motion unless an external Force acts on
0:4:10: it for example when we switch off a fan
0:4:15: it continues to rotate for a while due
0:4:17: to the inertia of
0:4:19: motion this is because the fan has
0:4:21: inertia of motion and tends to maintain
0:4:23: its speed and direction of
0:4:25: rotation another example of this is when
0:4:28: a moving bus suddenly stops people
0:4:30: inside might feel pushed
0:4:32: forward this happens because their
0:4:35: bodies want to keep moving even when the
0:4:37: bus stops so the bottom part of their
0:4:40: body that's touching the bus slows down
0:4:43: but the upper part keeps moving forward
0:4:45: for a moment before everything stops
0:4:48: together the inertia of direction is a
0:4:50: tendency of a body to maintain its
0:4:52: direction of motion unless an external
0:4:55: Force acts on it for example when a car
0:4:58: takes a sharp turn turn the passengers
0:5:0: sitting in the car feel a sideways push
0:5:4: this is because the passengers have
0:5:5: inertia of Direction and tend to move
0:5:8: along a straight line to make them move
0:5:11: along a curved path a force is required
0:5:15: the friction between the seats and the
0:5:16: passengers provides this Force another
0:5:20: example of inertia of direction is what
0:5:22: happens when a stone tied to a string is
0:5:24: worlded around in a circle the stone has
0:5:27: inertia of Direction and tends to move
0:5:30: along a straight line to make it move in
0:5:33: a circular path a force is required the
0:5:36: tension in the string provides this
0:5:38: Force what happens when the string is
0:5:41: cut the stone flies of tangentially due
0:5:44: to the inertia of
0:5:45: Direction the stone no longer has any
0:5:48: force acting on it to change its
0:5:50: direction of
0:5:51: motion now let's imagine you have two
0:5:54: tables in front of you one small and one
0:5:56: large now think about this if we gave
0:6:0: both tables the same push which one do
0:6:2: you think would be harder to move take a
0:6:5: moment to guess let's find out when we
0:6:10: push the small table and then the big
0:6:12: table with the same Force something
0:6:14: interesting happens the big table
0:6:17: doesn't budge easily does it it's almost
0:6:20: like it's saying nope I'm not
0:6:23: moving why do you think that is well
0:6:27: it's because the big table has more
0:6:29: stuff in it more mass and here's the
0:6:32: secret the more stuff or mass something
0:6:35: has the more it doesn't want to change
0:6:37: its
0:6:38: movement and what do we call when
0:6:40: something doesn't want to change we call
0:6:43: this inertia so here's the magical rule
0:6:47: the heavier something is the more
0:6:49: inertia it has that's it so the next
0:6:53: time your bus suddenly stops and you
0:6:55: fall over I want you to remember Newton
0:6:57: and his first law of motion
0:7:1: we hope that you have understood the
0:7:2: concept of Newton's first law of
0:7:5: motion now here's a secret on how you
0:7:8: can study effectively with the urv app
0:7:11: you can learn with chapter notes watch
0:7:14: video lectures and solve ncer based McQ
0:7:17: tests of this chapter on
0:7:20: urv and that's not all you also get
0:7:23: amazing courses for class 9 and much
0:7:25: more for your class 9
0:7:27: preparation thank you