Physics Work and Energy Concepts

Work

• Work occurs when an object is moved or rearranged by an applied force.
• Work is defined as a scalar quantity, calculated using the formula: Work (W) = Force (F) x Distance (d) or W = F x d.

Energy

• Energy is the ability to do work and is measured in joules (J).
• Energy causes movement, combustion, and the production of light and sound.
• Energy is not directly visible, but its effects can be observed.

Types of Energy with Examples

• Bricks and Pulley: The person pulling the bricks has the energy to lift them.
• Rock and Explosive: The explosive material possesses the energy to break the rock.
• Jack in the Box: The compressed spring holds elastic potential energy that transforms into kinetic energy when released.
• Windmill: Wind has kinetic energy that turns the vanes.
• Light Globe: The battery provides electrical energy that is converted into light.

Energy Transformation

• Energy can change from one form to another:
  • In a jack-in-the-box: Elastic Potential Energy → Kinetic Energy.
  • Electric light: Electrical Energy → Light Energy.
  • Hammering a nail: Kinetic Energy → Heat Energy.

Energy Converters

• Examples of energy conversion:
  • Chemical to Kinetic.
  • Electrical to Thermal.
  • Chemical to Electrical.
  • Electrical to Radiated.
  • Electrical to Sound.

Types of Energy Focus

• Kinetic Energy (KE): The energy of moving objects, calculated by KE = ½ x mass (m) x speed (v)².
• Gravitational Potential Energy (GPE): Energy based on an object's position in a gravitational field, calculated by GPE = mass (m) x gravitational field strength (g) x height (h).
  • Gravitational field strength (g) = 9.8 N/kg.
• Elastic Potential Energy (EPE): Energy in stretched or compressed objects, represented as EPE = ½ x spring constant (k) x extension/compression (e)².

Example of Kinetic Energy Calculation

• For a car with mass 1400 kg traveling at 40 km/hr:
  • Convert speed to m/s: 40 km/h = 11.1 m/s.
  • Calculate KE: KE = ½ x 1400 x (11.1)² = 86,247 J (or 86 kJ).
• If the car travels at 80 km/h, the kinetic energy increases to 344,988 J (or 345 kJ), highlighting that KE is proportional to the square of speed.

Law of Conservation of Energy

• The total energy in an isolated system remains constant; energy cannot be created or destroyed, only transformed from one form to another.