Work, energy and power are the central concepts of classical Physics. Work is the displacement of a body when a force (pull or push) is exerted on it. Energy is the capacity to do the work. Work done per given time is known as power.
Work
Work is the measure of energy transferred when a body is moved over a distance by an outside force that is exerted in the direction of the displacement. If the applied force is constant, work done can be calculated by multiplying the length of the path by the force component acting along the path. To represent this idea mathematically, the work W is equivalent to the force ‘F’ times the distance ‘d’ ( W = Fd). If the force is being applied at angle ‘θ’ to the displacement direction, then work w = Fdcosθ. Work done on an object is acquired not only by the object’s displacement as a whole from one position to another, but also by various other processes like rotating an axis, compressing a gas, particle motion within a body by an outside magnetic field. The work done is stated as the product of the force component in the displacement’s direction and value of this displacement. Among the work energy power trio, work is the most elementary concept.
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W = (F cos θ )d = F.d |
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It can be summarised that no work is produced if:
- The acquired displacement is zero, the applied force is zero.
- The force and displacement are at an angle of 90° with each other.
- The work’s SI unit is Joule (J). If a force of 10 newtons is exerted on a body and moves 5 metres, the work done will be 50 newtons per meter or 50 Joule (1J = 1N).
Energy
Energy is the ability or the capacity to do work. It may exist in the form of kinetic energy, potential energy, chemical energy, thermal energy, etc. In the case of heat and work, energy is the means of heat transfer from one system to another. After it has been transmitted, energy is always considered according to the nature acquired after transmission. So, the heat transmitted may become thermal form while work done may develop into the mechanical energy form.
In classical mechanics, all energy forms are connected to motion. For example, a body possesses kinetic energy when it is in motion. A body suspended on a spring (even though it is at rest) has certain potential energy for generating motion. It possesses potential energy due to its configuration. In the case of an atom, nuclear energy is the potential energy as it is the consequence of the arrangement of subatomic particles in an atom’s nucleus.
In SI units, energy is calculated in joules. A unit joule is equivalent to the work done by one unit newton force acting over a unit distance.
Kinetic energy is the energy that exists due to the motion of a body. A few examples are flowing water, moving buses, rolling balls, falling rockets, etc.
Kinetic energy
Where m is the mass of the body and v is the velocity of the body.
Potential energy is the energy accumulated in a body due to its height and position. It is calculated by the amount of work done. A few examples are a ball on a bench, water stored in a dam, etc.
Potential energy PE = mgh
Where m is the mass of the body, g is the acceleration due to the Earth’s gravity, and h is the height.
Power
Power is the quantity of energy converted or transferred per unit time. It is also expressed as the work done divided by the time period t. In the SI units, power is calculated in newton metres per second.
In the International System of Units, power is measured in newton metres per second.
Power can be found by dividing work done by time. The formula for power is:
P is the power, W is the work done by the body and Δt is the time taken.
The video is about the basic concepts of work, energy and power.
Important Work Energy Power Questions with Answers
1) Name the three central concepts of classical physics.
Work, Energy and Power are the central concepts of classical Physics. Work is the displacement of a body when a force (pull or push) is exerted on it. Energy is the capacity to do the work. Work done per given time is known as power.
2) What is meant by work?
Work is the measure of energy transferred when a body is moved over a distance by an outside force that is exerted in the direction of the displacement. If the applied force is constant, work done can be calculated by multiplying the length of the path by the force component acting along the path.
To represent this idea mathematically, the work W is equivalent to the force ‘F’ times the distance ‘d’ ( W = Fd). If the force is being applied at angle ‘θ’ to the displacement direction, then work w = Fdcosθ.
Work done on an object is acquired not only by the object’s displacement as a whole from one position to another, but also by various other processes like rotating an axis, compressing a gas, particle motion within a body by an outside magnetic field. The work done is stated as the product of the force component in the displacement’s direction and value of this displacement.
3) What is the formula for work?
The work done is stated as the product of the force component in the displacement’s direction and the value of this displacement.
W = (F cos θ )d = F.d
4) What are the conditions for work done to be zero?
It can be summarised that no work is produced if:
- The acquired displacement is zero.
- The applied force is zero.
- The force and displacement are at an angle of 90° with each other.
5) What is the SI unit of work?
The work’s SI unit is Joule (J). If a force of 10 newtons is exerted to a body and moves 5 metres, the work done will be 50 newtons per meter or 50 Joule (1J = 1N).
6) What is meant by energy?
Energy is the ability or the capacity to do work. It may exist in the form of kinetic energy, potential energy, chemical energy, thermal energy, etc. In the case of heat and work, energy is the means of heat transfer from one system to another. After it has been transmitted, energy is always considered according to the nature acquired after transmission. So, the heat transmitted may become thermal form while work done may develop into the mechanical energy form.
In classical mechanics, all energy forms are connected to motion. For example, a body possesses kinetic energy when it is in motion. A body suspended on a spring (even though it is at rest) has certain potential energy for generating motion. It possesses potential energy due to its configuration. In the case of an atom, nuclear energy is the potential energy as it is the consequence of the arrangement of subatomic particles in an atom’s nucleus.
7) What is the SI unit of energy?
In SI units, energy is calculated in joules. A unit joule is equivalent to the work done by one unit newton force acting over a unit distance.
8) What is meant by conservation of energy?
No energy can be created or destroyed, and it can only change from one type to another. This law is called conservation of energy. For example, when a car slips down from a slanted road, the potential energy that the vehicle has from being positioned high up on the slanted road is transformed into kinetic energy. As the car slows down to a halt through friction, the kinetic energy from the vehicle’s motion is transformed into thermal energy that heats the car’s surface, which is in contact with the road.
Energy can be changed from one type to another through different methods. For instance, electrical or mechanical energy is generated by various types of devices like generators, fuel cells, batteries, magnetohydrodynamic systems and heat engines.
9) What is meant by kinetic energy?
Kinetic energy is the energy that exists due to the motion of a body. A few examples are flowing water, moving buses, rolling balls, falling rockets, etc.
10) What is the formula for kinetic energy?
Where m is the mass of the body and v is the velocity of the body.
11) What is meant by potential energy?
Potential energy is the energy accumulated in a body due to its height and position. It is calculated by the amount of work done. A few examples are a ball on a bench, water stored in a dam, etc.
12) What is the formula for potential energy?
Potential energy PE = mgh
Where m is the mass of the body, g is the acceleration due to the Earth’s gravity, and h is the height.
13) What is meant by power?
Power is the quantity of energy converted or transferred per unit of time. It is also expressed as the work done divided by the time period t. In the SI units, power is calculated in newton metres per second.
14) What is the SI unit of power?
In the International System of Units, power is measured in newton metres per second.
Power can be found by dividing work done by time.
15) What is the formula for power?
p is the power, W is the work done by the body and Δt is the time taken.
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Practice Questions
1) What is the difference between energy and work?
2) What is the difference between kinetic energy and potential energy?
3) What is meant by thermal energy?
4) What are the two units of power?
5) What are the examples of kinetic energy and potential energy?
The below video helps to revise the concepts in the chapter Work and Energy Class 9
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