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# Test yourself now

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# Chapter 5: Work, energy and power

## 5.1 Introduction (ESCM9)

We use the term `work' in everyday conversation to mean many different things. We talk about going to work, doing homework, working in class. Physicists mean something very specific when they talk about work.

In Physics we use the term work to describe the process of transferring energy from object or system to another or converting energy from one form to another.

You will learn that work and energy are closely related to Newton's laws of motion. You shall see that the energy of an object is its capacity to do work and doing work is the process of transferring energy from one object or form to another by means of a force. In other words,

• an object with lots of energy can do lots of work.

• when object A transfers energy to object B, the energy of object A decreases by the same amount as the energy of object B increases, we say that object A does work on object B.

Lifting objects or throwing them requires that you do work on them. Even making an electrical current flow requires that something do work. Objects or systems must have energy to be able to do work on other objects or systems by transferring some of their energy.

• Units and unit conversions, Physical Sciences, Grade 10, Science skills
• Equations - Mathematics, Grade 10, Equations and inequalities
• Techniques of vector addition - Physical Sciences, Grade 10, Vectors and scalars
• Newton's laws - Physical Sciences, Grade 11, Forces
• Force diagrams - Physical Sciences, Grade 11, Forces

Work:

• Define word done on an object by a force.
• Understand that work is a scalar.
• Calculations done on the net work done on an object.
• Understand the difference of positive, negative and no work done.
• Drawing of force diagrams to determine the net work done on an object - Ignore perpendicular forces.

Work-energy theorem:

• Know the difference between conservative and non-conservative forces.
• Understand the result of a net force working in on an object.
• Application of the work-energy theorem to objects on horizontal and inclined planes.
• Calculations of different motions of objects.

Conservation of energy:

• Definition of conservative and non-conservative forces and examples.
• Know the relationship between conservative and non-conservative forces and mechanical energy.
• Calculations done on the conservation of energy.
• Using calculations to prove the relationship between non-conservative forces and mechanical energy.

Power:

• Definition of power as the rate at which work is done.
• Calculations done when work is done.
• Understand what is needed to keep an object moving at a constant speed.
• Calculations done when an object moves at a constant speed.
• Calculations done on power.
• Calculations done on maximum and minimum power.
• Units and unit conversions, Physical Sciences, Grade 10, Science skills
• Equations - Mathematics, Grade 10, Equations and inequalities
• Techniques of vector addition - Physical Sciences, Grade 10, Vectors and scalars
• Newton's laws - Physical Sciences, Grade 11, Forces
• Force diagrams - Physical Sciences, Grade 11, Forces