I need to update my previous comment with more current and correct information. The basic idea is that work is done at a constant velocity and balanced external forces are not needed for an object to move at a constant velocity. There is no distinction made between an object moving at a constant velocity with balanced external forces on it and an object moving at a constant velocity with no external forces acting on it. This is to say that the object is being displaced by its own momentum in both cases and ,therefore, that no work is being done by an external force on an object that is moving at a constant velocity with balanced external forces on it. So, the weight lifter in the video is not doing any work on the barbell that is moving up at a constant velocity. The external force by the weight lifter on the barbell is simply balancing out the external force of gravity allowing the barbell to be displaced upward by its own momentum. The truth is these are really external impulses on the barbell, but that's another story. Work is a vector quantity(i.e. it's not a scalar) and is defined as an inertial-displacement due to or caused by a force, a constant impulse, or a constant kinetic force acting for a time. I previously had labelled work as being a physical-displacement which is incorrect and it is an inertial-displacement. What the hell does this mean you ask? This is just a taste of what is modified kinematics which would describe the motion of a physical object with a resistance to change taken into account. It is necessary to take into account the inertia of a physical object when describing motion in order to understand what work really is or labelled as and to be able to define it. Inertia or mass resistance is the amount of matter resistance a physical object has to a change in its state of motion. Just like mass is the amount of matter, we have mass resistance which is the amount of matter resistance. Inertia is directly proportional to and depends on mass. The greater the mass that an object has the greater the inertia or mass resistance that the object has. Inertia(mass-resistance) ∝ mass Inertia(mass-resistance) = k*mass Inertia(mass-resistance) = (1)mass This means that inertia is a scalar quantity and has the same unit as mass. We can also refer to inertia using the term resistive-mass(mr) with "r" as a subscript as a reference to its resistance to change in its state of motion. We have an object such as the barbell being displaced at a constant velocity by its own momentum which means the weight lifter is not doing any work on it. However, there is work being done on it by its own momentum or kinetic force. What is kinetic force you may ask? Kinetic force is the force with which a body moves and is the velocity of a moving object in conjunction with its inertia or resistance to change. The kinetic force of a moving object tends to keep the object moving at a constant speed in the same direction, thereby displacing it. Kinetic force(k) = Inertia(resistive-mass) x velocity Displacement = vt Inertial-displacement = Inertia(resistive-mass) x displacement Inertial-displacement = Inertia(resistive-mass)x vt Inertial-displacement = Kinetic force(k) x time(t) The "inertial-displacement" done or work done by the kinetic force would be referred to as kinetic work. inertial-displacement = kt Kinetic-work(W) = kt Kinetic work is the inertial-displacement due to or caused by a constant kinetic force acting on an object for a time. You can see that we are multiplying a scalar(i.e. inertia) by a vector(i.e. displacement) for kinetic work which means that work is a vector quantity.
The concept of work in Physics is completely erroneous or wrong and work is not really force times displacement(F•d). The work done on an object does not reflect the energy transferred to the object neither. Instead, the amount of energy transferred to an object by an external force would reflect the magnitude of the external force on the object. Work is a vector quantity(i.e. it's not a scalar) and is defined as a "physical-displacement" by or due to a force, an impulse, or the kinetic force acting for a time. So, let's use the example in the video with a weight lifter lifting the barbell up and displacing it at constant speed. The "physical-displacement(ms)" is considered to be due to the kinetic force or momentum of the barbell and is calculated based on this. Displacement(s) Physical-displacement = mass(m) x displacement(s) Displacement(s) = vt Physical-displacement(ms) = mvt kinetic-force(k) = mv The "physical-displacement" done or work done by the kinetic force acting for a time would be referred to as kinetic work. We would ordinarily substitute physical-displacement(ms) with a "W" having a lower case "k" as a subscript to represent kinetic-work, but "W" will do. Physical-displacement(ms) = kt Kinetic-work(W) = kt
@@sciencylopedia7717 This all goes back to the beginning with experiments centuries ago by Willem Gravesande and others in which metal balls were dropped from varying heights onto a layer of soft clay and the craters left were compared. You can check out one of these experiments at the link here. The experiments were done based on the erroneous belief that the crater left by a ball (i.e. the work done by a ball) represented its kinetic energy. ruclips.net/video/mPLqqycxtYI/видео.html The energy transferred to the clay is not work and is not reflected in the crater itself, but rather it is reflected in the change in momentum of the clay in the formation of the crater. There is an unbalanced force on the clay by the ball that is acting for a period of time to displace material and form the crater. The work done is nothing more than the crater left by this unbalanced force acting on the clay for a period of time which is to say that there's nothing special about work.
@@sciencylopedia7717 The concept of physical-displacement is "matter-displacement" or ,so to speak, displacement with matter and is analogous to the concept of a physical object which is a "matter object". The term "physical" is used to refer to matter and is quantified in terms of mass. So, physical-displacement(ms) or matter-displacement is quantified in terms of mass(m) x displacement(s). I was mistaken with the example of the barbell being lifted up at constant speed because I learned or realized afterward that the physical-displacement of the barbell is not due to the kinetic-force or momentum of the barbell and ,hence, there is no work done by the momentum of the barbell. We would know this by the fact that the barbell would not continue to go up due to its momentum if you were to let go of it and let it fall. The momentum of an object can only do work if it carries or displaces the object and we can know whether it does by letting it go.
@@sciencylopedia7717 In order for you to start to understand how work is a vector you would need to refer to Kinematics and expand on it with the concept of physical-displacement by taking the mass of the object into account. Kinematics is the study of the motions of real-world or physical objects and by expanding on it with the concept of physical-displacement it would become the study of the physical motions or movements of physical objects. This may be referred to as Physical-Kinematics. This leads to equations for work and shows the fact that it depends on time. However, there's a lot more to it then this.
Thank you so much Dr. Edwards for explaining physics in simple and easy way . This is the type of explaination which Indian students need!!!
thank you
I need to update my previous comment with more current and correct information. The basic idea is that work is done at a constant velocity and balanced external forces are not needed for an object to move at a constant velocity. There is no distinction made between an object moving at a constant velocity with balanced external forces on it and an object moving at a constant velocity with no external forces acting on it. This is to say that the object is being displaced by its own momentum in both cases and ,therefore, that no work is being done by an external force on an object that is moving at a constant velocity with balanced external forces on it.
So, the weight lifter in the video is not doing any work on the barbell that is moving up at a constant velocity. The external force by the weight lifter on the barbell is simply balancing out the external force of gravity allowing the barbell to be displaced upward by its own momentum. The truth is these are really external impulses on the barbell, but that's another story.
Work is a vector quantity(i.e. it's not a scalar) and is defined as an inertial-displacement due to or caused by a force, a constant impulse, or a constant kinetic force acting for a time. I previously had labelled work as being a physical-displacement which is incorrect and it is an inertial-displacement. What the hell does this mean you ask? This is just a taste of what is modified kinematics which would describe the motion of a physical object with a resistance to change taken into account. It is necessary to take into account the inertia of a physical object when describing motion in order to understand what work really is or labelled as and to be able to define it.
Inertia or mass resistance is the amount of matter resistance a physical object has to a change in its state of motion. Just like mass is the amount of matter, we have mass resistance which is the amount of matter resistance. Inertia is directly proportional to and depends on mass. The greater the mass that an object has the greater the inertia or mass resistance that the object has.
Inertia(mass-resistance) ∝ mass
Inertia(mass-resistance) = k*mass
Inertia(mass-resistance) = (1)mass
This means that inertia is a scalar quantity and has the same unit as mass. We can also refer to inertia using the term resistive-mass(mr) with "r" as a subscript as a reference to its resistance to change in its state of motion.
We have an object such as the barbell being displaced at a constant velocity by its own momentum which means the weight lifter is not doing any work on it. However, there is work being done on it by its own momentum or kinetic force. What is kinetic force you may ask? Kinetic force is the force with which a body moves and is the velocity of a moving object in conjunction with its inertia or resistance to change. The kinetic force of a moving object tends to keep the object moving at a constant speed in the same direction, thereby displacing it.
Kinetic force(k) = Inertia(resistive-mass) x velocity
Displacement = vt
Inertial-displacement = Inertia(resistive-mass) x displacement
Inertial-displacement = Inertia(resistive-mass)x vt
Inertial-displacement = Kinetic force(k) x time(t)
The "inertial-displacement" done or work done by the kinetic force would be referred to as kinetic work.
inertial-displacement = kt
Kinetic-work(W) = kt
Kinetic work is the inertial-displacement due to or caused by a constant kinetic force acting on an object for a time. You can see that we are multiplying a scalar(i.e. inertia) by a vector(i.e. displacement) for kinetic work which means that work is a vector quantity.
Dr Edwards on Example 3, why is Work of static friction measured in Newtons?
There's a typo at 21:45. The work done by static friction should be in joules, not newtons. Sorry about that!
The concept of work in Physics is completely erroneous or wrong and work is not really force times displacement(F•d). The work done on an object does not reflect the energy transferred to the object neither. Instead, the amount of energy transferred to an object by an external force would reflect the magnitude of the external force on the object.
Work is a vector quantity(i.e. it's not a scalar) and is defined as a "physical-displacement" by or due to a force, an impulse, or the kinetic force acting for a time.
So, let's use the example in the video with a weight lifter lifting the barbell up and displacing it at constant speed. The "physical-displacement(ms)" is considered to be due to the kinetic force or momentum of the barbell and is calculated based on this.
Displacement(s)
Physical-displacement = mass(m) x displacement(s)
Displacement(s) = vt
Physical-displacement(ms) = mvt
kinetic-force(k) = mv
The "physical-displacement" done or work done by the kinetic force acting for a time would be referred to as kinetic work. We would ordinarily substitute physical-displacement(ms) with a "W" having a lower case "k" as a subscript to represent kinetic-work, but "W" will do.
Physical-displacement(ms) = kt
Kinetic-work(W) = kt
I understand your logic, and I want to know more. The internet has no mention of Work being a vector, can you elaborate please?
@@sciencylopedia7717 This all goes back to the beginning with experiments centuries ago by Willem Gravesande and others in which metal balls were dropped from varying heights onto a layer of soft clay and the craters left were compared. You can check out one of these experiments at the link here. The experiments were done based on the erroneous belief that the crater left by a ball (i.e. the work done by a ball) represented its kinetic energy.
ruclips.net/video/mPLqqycxtYI/видео.html
The energy transferred to the clay is not work and is not reflected in the crater itself, but rather it is reflected in the change in momentum of the clay in the formation of the crater. There is an unbalanced force on the clay by the ball that is acting for a period of time to displace material and form the crater. The work done is nothing more than the crater left by this unbalanced force acting on the clay for a period of time which is to say that there's nothing special about work.
@@sciencylopedia7717 The concept of physical-displacement is "matter-displacement" or ,so to speak, displacement with matter and is analogous to the concept of a physical object which is a "matter object". The term "physical" is used to refer to matter and is quantified in terms of mass. So, physical-displacement(ms) or matter-displacement is quantified in terms of mass(m) x displacement(s).
I was mistaken with the example of the barbell being lifted up at constant speed because I learned or realized afterward that the physical-displacement of the barbell is not due to the kinetic-force or momentum of the barbell and ,hence, there is no work done by the momentum of the barbell. We would know this by the fact that the barbell would not continue to go up due to its momentum if you were to let go of it and let it fall. The momentum of an object can only do work if it carries or displaces the object and we can know whether it does by letting it go.
@@sciencylopedia7717 In order for you to start to understand how work is a vector you would need to refer to Kinematics and expand on it with the concept of physical-displacement by taking the mass of the object into account. Kinematics is the study of the motions of real-world or physical objects and by expanding on it with the concept of physical-displacement it would become the study of the physical motions or movements of physical objects. This may be referred to as Physical-Kinematics. This leads to equations for work and shows the fact that it depends on time. However, there's a lot more to it then this.
@@sciencylopedia7717 So, nothing to comment on with my elaborate explanation?