Work and Energy Concepts

Work and Energy

• Work is done when energy is required
• Animals use food for energy; machines use fuel
• Reading, writing, and thinking don't require work scientifically
• Work is done when a force moves an object
• A body is stationary when there is zero work done
• Work is done when a moving object stops or starts moving
• Force applied to a body changes the velocity or shape to do work
• Force must be applied and the body must move for work to be done

Conditions of work done

• A force must be applied to the body.
• The body must be displaced.

Work is done when

• A person cycles
• A person lifts a weight

Work is not done when

• A person stands still carrying a load
• A person tries to move a large rock

Work done by a fixed force

• For a body in motion, the work done is the force multiplied with the displacement in the direction of the force
• Work = Force x Displacement (W = F x S)
• Work is a scalar quantity

Unit of Work

• The unit of work is Newton metre or Joule
• 1 Joule = 1 Newton x 1 metre (1 J = 1 Nm)

Work done against gravity

• When work is done against gravity, the amount of work done is equal to the product of the weight and the vertical distance moved
• Work (W) = Weight of the body x vertical distance
• W = m x g x h
• Where 'm' is mass, 'g' is acceleration due to gravity, and 'h' is the height

Factors affecting work done

• Magnitude of force: Greater the displacement, greater the amount of work and vice-versa.
• Displacement: Greater the displacement, greater the amount of work done, and the vice-versa

Negative, positive, and zero work

• Positive work: force acts in the direction of motion
• Negative work: force acts opposite to the direction of motion
• Zero work: force acts perpendicular to the direction of motion

Energy

• The capacity to do work is known as energy
• The sun is the biggest source of energy
• Energy comes from the sun (atoms, the interior of the earth, and the tides)

Forms of energy

• Mechanical energy: energy due to position or motion
• Kinetic energy: energy due to motion (e.g., moving cricket ball, flowing water, moving bullet, moving car, etc.)

Kinetic energy formula derivation

• Work done (W) = Force (F) x distance (s)
• W = 1/2 m (v² - u²)
• Work done = Change in kinetic energy
• KE = 1/2 m v²

Potential energy

• Energy due to position or shape is known as potential energy
• Example: water in a dam, wound-up spring of a toy car

Factors affecting potential energy

• Mass
• Height above the ground
• Change in shape

Transformation of energy

• Change of one form of energy to another form
• Example: A stone at a height has potential energy. As it falls, the potential energy changes to kinetic energy. At the bottom, kinetic energy is maximum.
• In a hydroelectric power plant, water potential energy transforms to kinetic energy, then electrical energy
• At thermal powerhouses, chemical energy transforms to heat energy, then to kinetic and electrical energy
• Plants transform solar energy to chemical energy in food

Laws of Conservation of energy

• Energy cannot be created or destroyed, only transformed
• Whenever energy changes form, the total amount of energy remains constant

Conservation of energy during free fall

• As a ball falls, its potential energy decreases, and kinetic energy increases
• The sum of potential and kinetic energy at all points in its fall remains constant

Rate of doing work - Power

• Power is the rate at which work is done (or energy is consumed)
• Power (P) = Work done (W) / Time taken (t)
• Unit of Power is Watt (W) = 1 Joule/second (1 J/s)

Commercial unit of energy

• A larger unit of energy used for commercial purposes is kilowatt-hour (kWh)
• 1kWh = 3.6 x 10⁶ J

Explore the principles of work and energy in this quiz. Understand how work is done, the conditions required, and the calculations involved. Test your knowledge on the applications of work in various scenarios.