Overview
This lecture covers the concept of energy, different energy stores, key equations for energy calculations, practical experiments, efficiency, and types of energy sources.
Energy Concepts and Conservation
- Energy is a number that describes what happens when objects interact within a system.
- Total energy in an interaction is always conserved; energy cannot be created or destroyed (except via mass-energy conversion in nuclear reactions).
- Energy is measured in Joules (J).
Types (Stores) of Energy
- Kinetic Energy: Calculated by ( E = \frac{1}{2}mv^2 ); depends on mass and speed.
- Gravitational Potential Energy (GPE): Calculated by ( E = mgh ); depends on mass, gravitational field strength, and height.
- Elastic Potential Energy: Calculated by ( E = \frac{1}{2}kx^2 ); depends on a spring's stiffness (k) and extension (x).
- Thermal Energy (Change): Calculated by ( E = mc\Delta T ); depends on mass, specific heat capacity, and temperature change.
- Chemical Potential Energy: Present in fuels and food; no specific equation at this level.
Energy Transfer and Closed Systems
- Energy transfers occur between objects or energy stores for any change in a system.
- In closed systems, no energy is lost to or gained from surroundings, allowing equations like energy lost = energy gained.
Example Calculations and Rearranging Equations
- For falling objects: GPE lost equals KE gained (( mgh = \frac{1}{2}mv^2 )).
- To solve for speed: ( v = \sqrt{2gh} ) if masses cancel out.
- Energy may be lost to surroundings if not a closed system, usually due to friction or air resistance.
Specific Heat Capacity Practical
- Measure the mass and temperature rise of a heated block to calculate specific heat capacity.
- Some energy is lost to surroundings, making measured SHC values higher than actual.
- Power (( P )) is the rate of energy transfer: ( P = \frac{E}{t} ) (watts = joules/second).
Efficiency
- Efficiency = useful energy out / total energy in (can use power values too).
- Efficiency may be given as a decimal or percentage; lost energy is often in the form of heat.
Energy Sources
- Finite (Non-renewable): Fossil fuels (coal, oil, gas) and nuclear fuel (uranium).
- Renewable: Wind, hydroelectric, solar, geothermal, and biofuels.
Key Terms & Definitions
- Energy Store — Form of energy kept in an object or system (e.g., kinetic, potential).
- Closed System — No energy enters or leaves the system.
- Specific Heat Capacity (SHC) — Energy needed to raise 1 kg of a substance by 1°C.
- Power (P) — Rate at which energy is transferred (watts, W).
- Efficiency — Ratio of useful energy output to total energy input.
Action Items / Next Steps
- Practice rearranging and using energy equations.
- Understand practical setups for measuring SHC.
- Review types of energy sources and their properties.