Understanding Energy: Types, Transfers, and Conservation

Energy

Energy is the ability to do work or cause change.

Kinetic Energy

Stored in moving objects.

Gravitational Potential Energy

Stored in objects at height.

Elastic Potential Energy

Stored in stretched or squashed objects.

Chemical Energy

Stored in fuels, food, and batteries.

Thermal Energy

Stored in hot objects.

Atomic/Nuclear Energy

Stored inside atoms.

Mechanical Energy Transfer

By forces (e.g., pushing/pulling).

Electrical Energy Transfer

By moving charges.

Energy Transfer by Heating

From hot to cold objects.

Energy Transfer by Radiation

Through light or sound waves.

Energy Transfer in Falling Objects

Gravitational potential energy → Kinetic energy (object speeds up).

Energy Transfer on Impact

Kinetic energy → Thermal energy & Sound energy (dissipated due to friction).

Law of Conservation of Energy

Energy cannot be created or destroyed, only transferred.

Importance of Conservation of Energy

It ensures that total energy remains constant in all processes.

Closed System

A system in which no energy is transferred to or from the surroundings.

Energy in Closed Systems

Energy transfers within the system, but the total energy remains the same.

Work in Science

Work is the energy transferred by a force.

Work Done Calculation

[ Work done (W) = Force (F) × Distance (s) ] (Unit: Joules (J), Newtons (N), Meters (m))

Work Done Against Friction

It is converted into thermal energy and dissipated.

Example of Work Done Against Friction

A car braking - Kinetic energy transfers to thermal energy in brake pads.

Change in Gravitational Potential Energy

[ ΔE_p = Mass (m) × Gravitational Field Strength (g) × Height Change (Δh) ] (Unit: Joules (J), Kilograms (kg), Newtons per kg (N/kg), Meters (m))

Factors Affecting Kinetic Energy

Mass - More mass = more KE; Speed - Higher speed = more KE.

Kinetic Energy Calculation

[ E_k = 1/2 × Mass (m) × Speed² ] (Unit: Joules (J), Kilograms (kg), Meters per second squared (m/s²))

Elastic Potential Energy Calculation

[ E_e = 1/2 × Spring Constant (k) × Extension² ] (Unit: Joules (J), Newtons per meter (N/m), Meters (m))

Efficiency of Energy Transfers

Efficiency = (Useful energy output / Total energy input) × 100

Dissipated Energy

Energy spread out to surroundings, often as heat.

Chemical Energy Definition

Stored in fuels, food, batteries.

Thermal Energy Definition

Stored in hot objects.

Kinetic Energy Definition

Stored in moving objects.

Gravitational Potential Energy Definition

Stored in objects at height.

Power in physics

Power is the rate at which energy is transferred or work is done.

Power calculation

[ P = \frac{E}{t} ] (Unit: Watts (W), Joules (J), Seconds (s))

Example of power in action

A stronger light bulb uses more power because it transfers more energy per second.

Efficiency calculation

[ \text{Efficiency} = \frac{\text{Useful energy output}}{\text{Total energy input}} \times 100 ]

How to make energy transfers more efficient

1. Lubrication - Reduces friction. 2. Insulation - Prevents thermal loss.

Electrical power calculation

[ P = V \times I ] (Unit: Watts (W), Volts (V), Amperes (A))

Electrical energy transfer in circuits

Electrical energy is transferred when charges move through a potential difference.

Formula for energy transfer in circuits

[ E = Q \times V ] (Unit: Joules (J), Charge (C), Volts (V))

Energy stores in everyday objects

Car moving → Kinetic energy; Ball lifted → Gravitational potential energy; Rubber band stretched → Elastic potential energy.

Specific heat capacity

The amount of energy needed to raise the temperature of 1kg of a substance by 1°C.

Specific heat capacity calculation

[ E = m \times c \times \Delta \theta ] (Unit: Joules (J), Kilograms (kg), J/kg°C, Degrees Celsius (°C))

Example of dissipated energy

A hot drink cooling down—thermal energy dissipates into the air.

Energy loss in wires

Some energy is lost as heat due to resistance.

How to reduce energy loss

Use low-resistance wires or cooling systems.

Difference between renewable and non-renewable energy sources

Renewable - Can be replenished (e.g., solar, wind, hydro); Non-renewable - Finite supply (e.g., coal, oil, gas).

Sankey diagrams

They show energy transfers, including useful vs wasted energy.

Thicker arrow in Sankey diagram

More energy is transferred.

Examples of wasted energy in homes

Heat loss from windows; Light bulbs emitting heat; Friction in appliances.

How to reduce wasted energy

Insulation, energy-efficient bulbs, low-friction devices.

Importance of sustainability in energy use

To reduce environmental impact and ensure long-term availability of resources.

Example of a sustainable energy solution

Solar panels—renewable & reduces carbon emissions.

How forces transfer energy

When a force acts on an object, it does work, transferring energy to the object.

Formula for force-related energy transfer

[ W = F \times d ] (Unit: Joules (J), Newtons (N), Meters (m))

Energy changes when a car slows down

Kinetic energy → Thermal energy (due to friction in brakes); Kinetic energy → Sound energy (from engine & tires).

How to minimize energy loss in vehicles

Efficient engines, aerodynamics, regenerative braking.

What happens during energy conversions

Some useful energy is transferred; Some energy is wasted or dissipated.

Example of energy conversion

A phone battery → Chemical energy → Electrical energy → Light & sound energy.