1. Energy Stores, Transferring Energy & Work Done

1. The Conservation of Energy

The most fundamental principle is that energy is never created or destroyed; it is only transferred between different forms and objects.

2. Energy Stores

When energy is transferred to an object, it is held in one of several "stores":

• Thermal (Internal): Heat energy related to an object's temperature.

• Kinetic: Energy of a moving object.

• Gravitational Potential: Energy an object has due to its position in a gravitational field.

• Elastic Potential: Energy held in a stretched or compressed object (like a spring).

• Chemical: Energy held in chemical bonds.

• Magnetic: Energy in magnetic fields.

• Electrostatic: Energy involving electric charges.

• Nuclear: Energy released by breaking atoms apart.

3. Energy Transfers

Energy moves between stores in four main ways:

• Mechanically: By a force doing work (e.g., stretching a band).

• Electrically: Through a moving charge (e.g., current in a circuit).

• Heating: Due to temperature differences.

• Radiation: Via waves such as light or sound.

4. Systems

In physics, a "system" is simply a collection of matter:

• Open System: Can exchange both energy and matter with the outside world. It can lose or gain energy.

• Closed System: Neither matter nor energy can enter or leave. The total energy remains constant, even if it is transferred within the system.

5. Work Done

"Work done" is another way of saying energy transferred. There are two main types:

• Mechanical Work: Involves using a force to move an object (e.g., kicking a ball transfers chemical energy from your leg to the ball's kinetic store).

• Electrical Work: Done when current flows (e.g., overcoming resistance in a wire).

Example: Friction and Braking When a train applies its brakes, friction does work. It transfers energy from the wheels' kinetic energy store to the thermal energy stores of the surroundings as heat.