What is Work? Video Lecture | Science for Grade 6

0:0:2: what is work there is a difference in
0:0:5: the way we use the term work in
0:0:6: day-to-day life and the way we use it in
0:0:9: science in everyday Talk work means
0:0:13: effort but in science work is about
0:0:16: moving things for example pushing a rock
0:0:19: with all your strength does not count as
0:0:21: work if it does not move climbing stairs
0:0:25: count as work because you are moving
0:0:27: yourself and going against gravity
0:0:30: in the world of science we cannot base
0:0:32: our explanations on
0:0:34: perception all the words must be
0:0:37: properly defined using clear terms and
0:0:39: parameters for which all agree so let us
0:0:42: first understand what work actually
0:0:44: means in the world of physics in
0:0:47: scientific terms work is defined as a
0:0:50: measure of energy transfer that occurs
0:0:52: when an object is moved by an external
0:0:54: Force along a
0:0:56: displacement it is the product of the
0:0:58: force acting on the object and the
0:1:0: distance it is moved in the direction of
0:1:2: the force let us try to understand by
0:1:5: using few simple
0:1:6: examples throwing a balling ball pushing
0:1:10: a boulder pulling a trolley are all
0:1:14: examples of work done in
0:1:16: physics so always remember in science
0:1:19: work is done when a force moves an
0:1:21: object a certain
0:1:23: distance it is considered no work done
0:1:25: if carrying a heavy load without moving
0:1:27: it even if it makes you tired
0:1:30: we will discuss it mathematically to
0:1:33: understand why no work done is
0:1:34: considered in this case mathematical
0:1:38: expression now we can say that work is
0:1:41: defined by two numerical parameters as
0:1:44: seen from the
0:1:45: definition
0:1:47: Force displacement in the direction of
0:1:50: force so formula for work done is force
0:1:53: ftimes displacement s the SI unit of
0:1:58: work is Jewel it is represented by the
0:2:1: letter G let us try an example you push
0:2:5: a box with a force of 10 Newtons and it
0:2:8: moves 5 m then the work done is 50 juw
0:2:12: it is now easier to comprehend by
0:2:14: carrying a heavy load without moving
0:2:17: much like a statue seller who Bears the
0:2:19: weight of his Goods on his head all day
0:2:21: is considered as doing no work according
0:2:24: to
0:2:26: physics isn't it
0:2:28: unfortunate let let's discuss why this
0:2:31: is so it is because since the goods are
0:2:33: on his head and are stationary they are
0:2:35: not moving therefore the distance
0:2:37: covered is zero therefore work which is
0:2:41: force times displacement is
0:2:44: zero Force at an angle so according to
0:2:48: the formula if we try to apply vertical
0:2:51: force on a block and it moves
0:2:53: horizontally is it considered work done
0:2:57: the answer to this question is a big
0:2:59: note no the reason is simple enough let
0:3:3: us revise the definition of work once
0:3:7: again see something
0:3:9: interesting yes there is a little catch
0:3:12: to the second condition it states that
0:3:15: displacement is in the direction of
0:3:17: force in the current scenario force and
0:3:20: displacement are not in the same
0:3:22: direction hence there is no work done
0:3:26: imagine a scenario in which instead of
0:3:28: pushing the Box horiz horizontally or
0:3:30: vertically you decide to push it at an
0:3:32: angle of theta de upward from the
0:3:35: horizontal direction from common
0:3:37: knowledge we know that the complete
0:3:39: force is not causing the motion of the
0:3:42: Box only a small part of the force is
0:3:45: responsible for motion to find the value
0:3:48: of this part of force we use the angle
0:3:50: between force and
0:3:52: displacement so now we can generate a
0:3:55: universal formula to calculate the work
0:3:57: done as work is equal to products of
0:4:1: force F displacement s and cosine of the
0:4:5: angle between them cos Theta now let us
0:4:8: try to solve a problem you are pushing a
0:4:11: box at an angle 60° from horizontal
0:4:14: Direction the Box moves 5 m horizontally
0:4:18: but now the angle between the force and
0:4:20: the displacement is
0:4:22: 60° to calculate the work done in this
0:4:25: case use the formula W is equal to f * s
0:4:29: * cos Theta here f is still the force 10
0:4:33: Newtons s is the displacement 5 m and
0:4:37: Theta is now
0:4:39: 60° the cosine of 60° is a half or
0:4:43: 0.5 therefore the work done is W is
0:4:47: equal to 10 * 5 * 0.5 which is 25
0:4:53: JW types of work done now let us
0:4:57: understand how to represent different
0:4:59: types of work done work done can be
0:5:2: positive negative or even zero depending
0:5:6: on the angle between the force and
0:5:8: displacement let's explore these with
0:5:11: examples positive work done when the
0:5:15: angle between force and displacement is
0:5:17: acute that is angle is less than 90° the
0:5:21: work done is positive a gardner pushes a
0:5:24: lawn roller through a distance applying
0:5:26: a force at an angle Theta de to the
0:5:29: ground which is an acute angle the work
0:5:32: done by the gardener is force time
0:5:34: displacement time cos Theta and it is
0:5:37: positive zero work done when the angle
0:5:41: between force and displacement is 90°
0:5:44: the work done is Zer as work done equals
0:5:47: force time displacement time cos Theta
0:5:50: and since cos 90 is 0 hence work done is
0:5:53: 0o Imagine lifting a book and placing it
0:5:56: back on the same shelf if you lift it up
0:6:0: and then put it back down without moving
0:6:2: it horizontally the work done is zero
0:6:5: because there's no net displacement in
0:6:7: the direction of the force applied for a
0:6:10: body moving in a circular path the work
0:6:12: done by the centripetal force is zero
0:6:15: since the force is perpendicular to the
0:6:18: displacement negative work done when the
0:6:21: angle between force and displacement is
0:6:24: 180° as cos 180 is minus1 so the work
0:6:29: done is
0:6:30: negative this often occurs when dealing
0:6:33: with friction a block is pushed by a
0:6:36: force and displaced through a
0:6:38: distance the work done by the applied
0:6:40: force is positive while the work done by
0:6:43: the frictional force is negative as the
0:6:45: frictional force Works opposite to the
0:6:47: direction of displacement and hence the
0:6:50: angle between the frictional force and
0:6:52: the direction of displacement is
0:6:55: 180° work done is maximum when the angle
0:6:58: is 0°
0:7:0: as work done is force time displacement
0:7:2: time cos Theta and as the value of cos0
0:7:5: is 1 hence work is force times
0:7:7: displacement only which is the maximum
0:7:10: work done and it happens when the force
0:7:12: acts in the direction of the
0:7:17: displacement
0:7:19: conclusion in physics work is a dance of
0:7:22: forces and movements involving Push Pull
0:7:25: and
0:7:26: angles it's the story of how energy
0:7:28: moves when when we push lift or deal
0:7:31: with obstacles like
0:7:34: friction we hope that you have
0:7:36: understood the concept of work now
0:7:39: here's a secret on how you can study
0:7:42: effectively with the urv app you can
0:7:45: learn with chapter notes watch video
0:7:47: lectures and solve ncer based McQ tests
0:7:51: of this chapter on
0:7:52: urv and that's not all you also get
0:7:55: amazing courses for class 9 and much
0:7:58: more for your class 9
0:8:0: preparation thank you