Title:What is Work in Physics?
Introduction:
In Physics, the concept of What is Work ?plays a pivotal role in understanding how forces cause movement and how energy is transferred or transformed in physical systems. The term "work" in physics has a precise definition, different from its everyday use, where it generally refers to any physical or mental effort. In physics, work is a fundamental concept that connects force, displacement, and energy, serving as a cornerstone in mechanics, thermodynamics, and various other domains of physics.
In his article I will try to delve into the definition of What is Work in Physics?, the mathematical formulation, the different types of work, the relationship between work energy, power and various applications of the concept in understanding natural phenomena.
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Explanation:
Let, us start with What is Work in Physics?
Definition of Work in Physics:
Work, in the context of physics, is defined as the process of energy transfer when a force is applied to an object, causing it to move in the direction of the force.
Mathematically, work (W) is expressed as:
W=F⁻⁻>d⁻⁻>=Fd cosθ
Where,
W is the work done by the force,
F⁻⁻> is the vector representing the force applied,
d⁻⁻> is the vector representing the displacement of the object,
F is the magnitude of the force,
d is the magnitude of the displacement,
θ is the angle between the force vector and the displacement vector.
Work is a scalar quantity, meaning it has magnitude but no direction
The unit of work in the International System of Units (SI) is the joule (J), where one joule is equivalent to one newton-meter (1 J=1 N⋅m)
Again, in simple words, work can be defined as, force x displacement or W = F x d
What is 1 J ?
FAQ
Answer: When 1N force is applied on a body which at rest and it displaced 1m in the direction of force i.e; if it achieved 1 m displaced then the work which is done is called 1J.
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Answer: When 1N force is applied on a body which at rest and it displaced 1m in the direction of force i.e; if it achieved 1 m displaced then the work which is done is called 1J.
Some problems related on work:
FAQ
Answer: Here,
Force (F) = 5N
Displacement (d) =2m
∴ Work = F x d
= ( 5 x 2)
= 10 J
Question(2)
How much work has to be done to increase the velocity of a car from 30 ms⁻¹ to 60 ms ⁻¹, if the mass of the car is 1500kg.
FAQ
Answer: As we know that the capacity of doing work is called energy. So energy and work are same.
Here,
mass of the car (m) = 1500 kg
1st case, velocity (v₁) = 30 ms⁻¹
2nd case, velocity(v₂) = 60 ms⁻¹
∴ Required work done will be
= ½ m (v₂² - v₁²)
= ½ x 1500 ( 60² - 30² ) [putting values]
= 750 x (3600 - 900)
= 750 x 2700
= 2025000 J
= 2025 kJ [ ∵ 1000 J = 1 kJ]
--
Answer: Here,
Force (F) = 5N
Displacement (d) =2m
∴ Work = F x d
= ( 5 x 2)
= 10 J
Question(2) How much work has to be done to increase the velocity of a car from 30 ms⁻¹ to 60 ms ⁻¹, if the mass of the car is 1500kg.
Answer: As we know that the capacity of doing work is called energy. So energy and work are same.
Here,
mass of the car (m) = 1500 kg
1st case, velocity (v₁) = 30 ms⁻¹
2nd case, velocity(v₂) = 60 ms⁻¹
∴ Required work done will be
= ½ m (v₂² - v₁²)
= ½ x 1500 ( 60² - 30² ) [putting values]
= 750 x (3600 - 900)
= 750 x 2700
= 2025000 J
= 2025 kJ [ ∵ 1000 J = 1 kJ]
Historical Context and Development:
The concept of work has evolved over centuries, deeply intertwined with the development of classical mechanics. The idea of work was formalized during the 18th and 19th centuries as scientists began to understand the relationship between force, motion, and energy.
The term "work" in the scientific context was first introduced by the French mathematician Gaspard-Gustave Coriolis in the early 19th century. Coriolis was instrumental in defining work as the product of force and distance moved by the force in the direction of its action. This formalization was crucial in linking the concept of work to energy, setting the stage for the development of the law of conservation of energy.
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The concept of work has evolved over centuries, deeply intertwined with the development of classical mechanics. The idea of work was formalized during the 18th and 19th centuries as scientists began to understand the relationship between force, motion, and energy.
The term "work" in the scientific context was first introduced by the French mathematician Gaspard-Gustave Coriolis in the early 19th century. Coriolis was instrumental in defining work as the product of force and distance moved by the force in the direction of its action. This formalization was crucial in linking the concept of work to energy, setting the stage for the development of the law of conservation of energy.
Mathematical Formulation of Work:
The mathematical expression for work, W=Fdcosθ, encapsulates several critical aspects of the physical process:
a. Magnitude of force and Displacement:
The work done depends on the magnitude of the force applied and the displacement of the object. If either the force or the displacement is zero, no work is done. This means that even if a significant force is applied, if there is no movement, the work done is zero.
b. Directionality and the Cosine Component
The angle θ between the force and the displacement is crucial. The cosine component cosθ determines the effective part of the force that contributes to the work done. The scenarios include:
When θ=0°(force and displacement are in the same direction), cos0∘=1, and work is maximized as W=Fd.
When θ=90°(force and displacement are perpendicular), cos90°=0, and no work is done as W=0.
When θ=180°(force and displacement are in opposite directions), cos180°= - 1, and work is negative, indicating that the force is acting against the displacement.
--
The mathematical expression for work, W=Fdcosθ, encapsulates several critical aspects of the physical process:
a. Magnitude of force and Displacement:
The work done depends on the magnitude of the force applied and the displacement of the object. If either the force or the displacement is zero, no work is done. This means that even if a significant force is applied, if there is no movement, the work done is zero.
b. Directionality and the Cosine Component
The angle θ between the force and the displacement is crucial. The cosine component cosθ determines the effective part of the force that contributes to the work done. The scenarios include: When θ=0°(force and displacement are in the same direction), cos0∘=1, and work is maximized as W=Fd. When θ=90°(force and displacement are perpendicular), cos90°=0, and no work is done as W=0. When θ=180°(force and displacement are in opposite directions), cos180°= - 1, and work is negative, indicating that the force is acting against the displacement.
Positive, Negative, and Zero Work :
Positive Work: Positive Work occurs when the force component is in the same direction as the displacement, resulting in the energy being transferred to the object.
Negative Work: Negative Work occurs when the force component is in the opposite direction to the displacement, indicating that energy is taken from the object.
Zero Work: Zero Work occurs when the force is perpendicular to the displacement or when there is no displacement at all.
Types of Work in Physics:
Work can be classified into different types based on the context and the nature of the forces involved:
a. Mechanical Work
Mechanical work refers to the work done by forces that cause the movement of objects. It is the most common type of work encountered in classical mechanics and includes scenarios like lifting an object, moving a block along a surface, or pushing a car
b. Gravitational Work
Gravitational work involves the work done by gravitational forces. For example, when an object is lifted against the gravitational pull of the Earth, work is done by the lifting force, and the object gains gravitational potential energy.
W=mgh
Where,
m is the mass of the object,
g is the acceleration due to gravity,
h is the height the object is lifted.
c. Elastic Work
Elastic work is the work done when deforming an elastic object, such as stretching or compressing a spring. Hooke's Law governs the relationship between the force applied and the deformation in such cases. The work done in stretching or compressing a spring is given by,
W = ½ kx²
Where,
k is the spring constant,
x is the displacement from the equilibrium position.
d. Work Done by a Variable Force
In many real-world scenarios, the force applied to an object may not be constant. In such cases, the work done is calculated using calculus, integrating the force over the displacement,
W=
∫ F(x).dx
This approach is crucial for analyzing systems where the force changes with position, such as in gravitational fields, electric fields, or when dealing with non-linear springs.
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Work can be classified into different types based on the context and the nature of the forces involved:
a. Mechanical Work
Mechanical work refers to the work done by forces that cause the movement of objects. It is the most common type of work encountered in classical mechanics and includes scenarios like lifting an object, moving a block along a surface, or pushing a car
b. Gravitational Work
Gravitational work involves the work done by gravitational forces. For example, when an object is lifted against the gravitational pull of the Earth, work is done by the lifting force, and the object gains gravitational potential energy.
W=mgh
Where,
m is the mass of the object,
g is the acceleration due to gravity,
h is the height the object is lifted.
c. Elastic Work
Elastic work is the work done when deforming an elastic object, such as stretching or compressing a spring. Hooke's Law governs the relationship between the force applied and the deformation in such cases. The work done in stretching or compressing a spring is given by,
W = ½ kx²
Where,
k is the spring constant,
x is the displacement from the equilibrium position.
d. Work Done by a Variable Force
In many real-world scenarios, the force applied to an object may not be constant. In such cases, the work done is calculated using calculus, integrating the force over the displacement,
W= ∫ F(x).dx
This approach is crucial for analyzing systems where the force changes with position, such as in gravitational fields, electric fields, or when dealing with non-linear springs.
Work-Energy Theorem:
The work-energy theorem is a fundamental principle that relates the work done on an object to its kinetic energy. It states that the net work done on an object is equal to the change in its kinetic energy,
Wₙ = Δ K = ½ mvᵢ² - ½ mvₘ²
Where:Wₙis the net work done on the object,
Δ K is the change in kinetic energy,
m is the mass of the object,
vᵢ is the initial velocity,
vₘis the final velocity.
This theorem is a powerful tool in mechanics, allowing the prediction of an object's motion and speed after a force is applied.
--
The work-energy theorem is a fundamental principle that relates the work done on an object to its kinetic energy. It states that the net work done on an object is equal to the change in its kinetic energy,
Wₙ = Δ K = ½ mvᵢ² - ½ mvₘ²
Where:Wₙis the net work done on the object,
Δ K is the change in kinetic energy,
m is the mass of the object,
vᵢ is the initial velocity,
vₘis the final velocity.
This theorem is a powerful tool in mechanics, allowing the prediction of an object's motion and speed after a force is applied.
Work and Energy Conservation:
The concept of work is deeply linked to the law of conservation of energy, one of the most fundamental principles in physics. According to this law, energy cannot be created or destroyed, only transferred or transformed from one form to another.
a.Work and Kinetic Energy
As mentioned in the work-energy theorem, the work done on an object results in a change in its kinetic energy. If positive work is done on the object, its kinetic energy increases. Conversely, if negative work is done, its kinetic energy decreases.
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The concept of work is deeply linked to the law of conservation of energy, one of the most fundamental principles in physics. According to this law, energy cannot be created or destroyed, only transferred or transformed from one form to another.
a.Work and Kinetic Energy
As mentioned in the work-energy theorem, the work done on an object results in a change in its kinetic energy. If positive work is done on the object, its kinetic energy increases. Conversely, if negative work is done, its kinetic energy decreases.
Some problems on Kinetic Energy:
Question(1) A body of mass 13 kg moving with a uniform velocity of 4 ms⁻¹, find its kinetic energy.
Answer: Here,
Mass of the body (m) = 13 kg
Uniform velocity (v) = 4 ms⁻¹
∴ Kinetic energy (Ke) = ½ mv²
= ½ x 13 x 4 x 4 [putting values]
= 13 x 2 x 4
= 104 J
Question(2) A car with mass 1500kg moving with a speed 60 kmh⁻¹,to stop this car what amount of work has to be done.
Answer: Here,
mass of the car (m) = 1500 kg
speed of the car (v) = 60 kmh⁻¹
= (60 x 1000) / 3600 [∵1km =1000m and 1hr = 3600s]
= 1000 / 60
= 16.666….
= 16.67 ms⁻¹ (approximately)
∴ Work has to be done to stop the car
= ½ mv²
= ½ x 1500 x 16.67 x 16.67 [putting values]
= 750 x 277.8889
= 208416.675
= 208417 J (approx.)
b.Work and Potential Energy
Work done against conservative forces like gravity or spring force is stored as potential energy. For example, lifting an object increases its gravitational potential energy, while compressing a spring increases its elastic potential energy.
Some problems related on Potential Energy:
Question(1)
A ball has a mass 5kg is lifted at a height 10 meter from the ground find its potential energy. (Take g = 10 m/s²)
FAQ
Answer: Here,
Mass (m) = 5 kg
Height (h) = 10m
g = 10 m/s²
∴ Potential Energy = mgh
= 5 x 10 x 10
= 500 J
Question(2)
To lift a mass of 50 kg at some height 500 J work has been done.Find the height.(Take g = 10 m/s²)
FAQ
Answer: Here,
Mass (m) = 50kg
work (w) = 500 J
g = 10m/s
Let, height = h meter
∴ Height (h) = w / mg
= 500 / (50 x 10) [ Here, work = mgh]
= 500 / 500
= 1 m
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Question(1) A ball has a mass 5kg is lifted at a height 10 meter from the ground find its potential energy. (Take g = 10 m/s²)
Answer: Here,
Mass (m) = 5 kg
Height (h) = 10m
g = 10 m/s²
∴ Potential Energy = mgh
= 5 x 10 x 10
= 500 J
Question(2) To lift a mass of 50 kg at some height 500 J work has been done.Find the height.(Take g = 10 m/s²)
Answer: Here,
Mass (m) = 50kg
work (w) = 500 J
g = 10m/s
Let, height = h meter
∴ Height (h) = w / mg
= 500 / (50 x 10) [ Here, work = mgh]
= 500 / 500
= 1 m
Power: The Rate of Doing Work:
Power is the rate at which work is done or energy is transferred. It quantifies how quickly work is performed and is given by,
P=W/t
Where,
P is the power,
W is the work done,
t is the time taken.
The SI unit of power is the watt (W), where one watt is equivalent to one joule per second (1 W =1J/s)
Power is a crucial concept in understanding how efficiently work is performed in mechanical systems, engines, and electrical circuits.
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Some problems related on Power:
Question(1) A boy has a mass of 50kg climbed up 45 stairs in 9 secs,height of each stair is 15 cm,find the power of the boy.(Take g = 10m/s²)
Answer: Here,
Mass of the boy(m) = 50kg
Height (h) = (45 x 15) cm
= (675 /100)m [∵100cm =1m]
= 6.75 m
Acceleration due to gravity(g) = 10m/s²
Time(t) = 9sec
∴ Work has been done by the boy (w)= mgh
= (50 x 10 x 6.75)[putting values]
= 3375.00
= 3375 J
∴ Power of the boy = w/t
= 3375/9 Jsec⁻¹
= 375 watt.
Question(2) A body of mass 12 kg is kept at a height from the ground,if the potential energy of the body is 480 J,then find the height of the body from the ground.(Take g =10m/s²)
Answer: 1st Method,
Here,
mass of the body (m) =12kg
Acceleration due to gravity(g) = 10m/s²
Potential energy (P.E) = 480 J
∴height of the body(h) from the ground = P.E /(mxg)
= 480/(12x10)[putting values]
= 480/120
= 4 m
2nd Method,
Here,
mass of the body (m) =12kg
Acceleration due to gravity(g) = 10m/s²
Potential energy (P.E) = 480 J
Let height of the body from the ground = h meter
A/Q,
mgh = 480
=>12 x10 x h = 480
=> 120 h = 480
=> h = 480 /120
=> h = 4
∴height of the body(h) from the ground = 4m
Work in Different Physical Systems:
The concept of work extends beyond simple mechanical systems and is applicable in various fields of physics, including thermodynamics, electromagnetism, and quantum mechanics.
a. Work in Thermodynamics
In thermodynamics, work is associated with the transfer of energy between a system and its surroundings. It is often related to the expansion or compression of gases. For example, in an ideal gas undergoing expansion, the work done by the gas is given by,
w =∫ P.dv
Where
P is the pressure of the gas,
V is the volume of the gas.
This work is crucial in understanding heat engines, refrigerators, and various other thermodynamic processes.
b. Work in Electromagnetism
In electromagnetism, work is done when a charge moves in an electric field. The work done on a charge q moving through a potential difference V is given by
W=qV
This relationship is fundamental in the study of electric circuits, capacitors, and the energy stored in electric fields.
Some problems related on work in electromagnetism:
Question(1) An electric bulb of 60w is used 6hr/day, find the energy consumed by the bulb in units in a day.
Answer:
Here,
Power(P) = 60w
= 60 /1000 kw [ ∵ 1000 w = 1kw]
= .06 kw
Time (t) = 6hrs
∴ Energy consumed by the bulb(w) = P x t
= .06 x 6
= . 36 kwhr
= .36 units [∵1kwhr = 1unit]
Question(2) In a house energy consumed in a month is 250 unit,how much will be this energy in joule unit?
Answer: Energy (w) = 250 unit
= 250 kwhr [∵ 1unit = 1kwhr]
= (250 x 3.6 x 10⁶ J [1kwhr = 3.6 x 10⁶ J]
= 250 x 3.6 x 1000000 J
= 900,000,000 J
c.Work in Quantum Mechanics
In quantum mechanics, the concept of work is more abstract but still essential. Work can be related to the change in the quantum state of a system or the energy associated with a particle's wavefunction. Though the classical definition of work is not directly applicable, the principles of energy transfer and conservation remain relevant.
Practical Examples and Applications of Work:
The concept of work is not just theoretical; it has numerous practical applications in everyday life and technology.
a.Lifting Objects
When we lift a heavy object, you are doing work against the force of gravity. The energy we expend is transferred to the object as gravitational potential energy, which can be released if the object falls.
b.Machines and Engines
Machines like levers, pulleys, and engines are designed to do work more efficiently. For example, an internal combustion engine does work by converting chemical energy from fuel into mechanical energy, which powers a vehicle.
c.Electrical Appliances
Electric appliances like fans, refrigerators, and computers do work by converting electrical energy into mechanical work, cooling, or processing data. The power rating of these devices indicates how much work they can do in a given time.
Misconceptions about Work in Physics:
Several misconceptions about work in physics often arise due to the difference between its scientific and everyday meanings.
a. Work is Always Associated with Physical Effort
In physics, work can be done even if there is no visible physical effort, as long as there is a force causing displacement. For example, a battery doing work to power a device involves no physical effort but is still a form of work.
b. Work Always Results in Motion
While work generally involves movement, there are cases where energy is transferred without visible motion. For example, in lifting an object, work is done even if the object is held stationary at a height, as energy is stored as potential energy.
Conclusion:
What is Work in Physics is a fundamental concept that bridges the gap between force and energy. By understanding work, we can explain how forces cause motion, how energy is transferred and transformed, and how different physical systems operate. From the simple task of lifting a book to the complex processes inside an engine, the concept of work is integral to our understanding of the physical world.
In summary, work in physics is the energy transferred to or from an object via the application of force along a displacement. It is a concept deeply embedded in the fabric of classical mechanics, thermodynamics, electromagnetism, and beyond. As we continue to explore the physical world, the concept of work will remain a vital tool in our quest to understand and manipulate the universe.
-- FREQUENTLY ASKED QUESTIONs ON WHAT IS WORK?
(i).SI unit of work
+Answer:S.I unit of work is Joule.
(ii).What best defines work?
+Answer:When an external force is applied on a body and if the body is displaced in the direction of force; if the body gets a displacement in the direction of force then,in science it is called work has been done or simply work.
(iii).What is work definition class 10?
+Answer:If a force is applied from outside to a body which is rest is displaced and it occurs a motion,i.e;the body is displaced in the direction of applied force , then it is called work.
(iv).What is 1 joule in CGS?
+Answer:∵ 1Joule = 1Newton x 1meter
= 1N x 1m
= 10⁵ dyne x 100 cm
= 10⁵ x 10² dyne X cm
= 10⁷ erg
So, 1 joule in CGS system is 10⁷ erg
(v).What is SI unit of energy?
+Answer:As, we know the ability of doing work is called energy.
So, S.I unit of work and energy are same and it is Joule.
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