Class 9 Exam > Class 9 Videos > Science Class 9 > What is Work?
What is Work? Video Lecture | Science Class 9
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FAQs on What is Work? Video Lecture - Science Class 9
| 1. What is the definition of work? |  |
Ans. Work is defined as the physical or mental effort exerted in order to achieve a specific task or goal. It involves the application of force or the use of skills and abilities to accomplish something.
| 2. How is work measured? | |
Ans. Work is typically measured in terms of the amount of energy transferred or the force applied over a certain distance. The standard unit of work is the joule (J), which is equal to the amount of work done when a force of one newton is applied over a distance of one meter.
| 3. What are the different types of work? | |
Ans. Work can be classified into various types based on the nature of the task. Some common types of work include physical work (e.g., lifting objects, construction), mental work (e.g., problem-solving, analysis), artistic work (e.g., painting, writing), and social work (e.g., community service, counseling).
| 4. How is work different from power? | |
Ans. Work and power are related concepts, but they are not the same. Work refers to the amount of energy transferred or the force exerted to accomplish a task, while power is the rate at which work is done or the amount of work done per unit of time. In other words, work measures the total effort, while power measures how quickly that effort is applied.
| 5. Can work be negative? | |
Ans. Yes, work can be negative. In physics, work is considered negative when the force applied is in the opposite direction to the displacement. For example, if you push a box uphill, the work done by your force is negative because the force opposes the displacement. Negative work indicates that energy is being taken away from the system rather than being added to it.
Text Transcript from Video
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
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
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Oct 24, 2024 Last updated |
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