Energy Stores and Energy Transfers - Forces and Movement

Key Points

• Energy exists in different stores.
• Energy cannot be created or destroyed, only transferred between energy stores.
• Some energy transfers are beneficial, others are not.

What is Energy?

• Energy is a core concept in physics, helping us predict outcomes.
• Not directly visible but can be compared to money:
  • Stored in different forms like bank accounts or wallets.
  • Transferred between different stores.
• Energy is stored in various forms:
  • Thermal store of a hot object.
  • Kinetic store of a moving object.
• The unit of energy is the Joule (J).

Energy Stores

• Various forms of energy stores exist.
• Example: A sprinter increases their kinetic store as they speed up.

Energy Transfers

• Energy is transferred from one store to another through different processes:
  1. Mechanical Work: Force applied to move an object (e.g., lifting a book).
  2. Electrical Work: Charges flow in electricity (e.g., battery-powered train).
  3. Heat Transfer: Energy moves from a hot object to a cooler one (e.g., hand warmer).
  4. Radiation: Energy transfer via waves (e.g., infra-red radiation from a grill).

Work

• Work is performed when a force moves an object.
• It measures energy transferred when a force acts over a distance.
  • Energy transferred = Work
  • Both energy and work are measured in Joules (J).

Work Done Equation

• Formula: Work done (J) = Force (N) x Distance (m)
• Work is not an energy store but a method of energy transfer.

How to Calculate Work

• Example: Lifting a toy dragon weighing 30 N to 2 m height.
  • Formula: W = 30 N x 2 m
  • Result: W = 60 J

How to Calculate Force

• Rearrange work equation to find force: W = F x d
  • Formula rearranged: F = W/d
  • Example: Dragging a heavy object 5 m with 4000 J of work.
    • Calculation: F = 4000 J / 5 m = 800 N

How to Calculate Distance Moved

• Rearrange work equation to find distance: W = F x d
  • Formula rearranged: d = W/F
  • Example: Lifting an object 3 m with 210 J of work.
    • Calculation: d = 210 J / 70 N = 3 m

Test Your Knowledge

• A quiz is provided for self-assessment.