Heat Transfer, Energy Types, and Motion Principles

Heat and Thermal Equilibrium

Heat is a way to transfer energy, measured in Joules (J) by the SI. It can also be measured in calories (cal), where 1 cal = 4.184 J and 1 kJ = 1000 J. Heat can be transferred in three ways: conduction, convection, and radiation.

Conduction

Conduction is the process of heat transfer within a solid. Thermal energy is transferred, not matter. Thermal conductivity is the ability of a substance to conduct heat. Thermal conductors transfer thermal energy quickly, while thermal insulators transfer it slowly.

Convection

Convection is the transfer of thermal energy in a fluid (liquid or gas) due to fluid movement. Thermal energy is transmitted through the transport of matter. Convection currents occur when heating water.

Radiation

Radiation is heat transfer through emitted energy that can move through a vacuum. Thermal energy is transferred without a medium.

Thermal Equilibrium

When bodies at different temperatures come into contact, heat flows until they reach thermal equilibrium.

Energy and Its Forms

Energy is a property of matter that produces changes. It exists in different forms:

• Mechanical energy: Kinetic and potential (Em = Ec + Ep)
• Chemical energy: e.g., batteries
• Electromagnetic energy: e.g., X-rays/gamma
• Thermal energy: temperature
• Nuclear energy: En - Et - Eelectrica
• Electric energy: e.g., car battery
• Internal energy: energy inside a body

Renewable and Non-Renewable Energy

• Renewable: solar, biofuel, wind, tidal, hydroelectric, geothermal
• Non-Renewable: nuclear, fossil fuels

Law of Conservation of Energy

Energy transforms from one type to another, but the total energy remains constant. “Energy is neither created nor destroyed, it only transforms.”

Mechanical Energy

Mechanical energy is related to the position and movement of bodies. It is the sum of kinetic and gravitational potential energy.

Kinetic Energy

Kinetic energy is the energy of motion, related to mass and speed. It is calculated as: Ec = 1/2 mv²

Gravitational Potential Energy

Gravitational potential energy is the energy due to gravity, related to the position of a body relative to the ground (h). It is calculated as: Ep = mgh

Total Mechanical Energy

Mechanical Energy = kinetic energy + gravitational potential energy. Em = Ec + Ep = 1/2 mv² + mgh

Frame of Reference and Motion

A frame of reference determines if something is at rest or in motion. Position is the location of a body relative to a frame of reference, given as a distance. Displacement is the straight-line distance between two positions of a moving object. Trajectory is the path a body takes, which can be a straight line or a curve. Distance travelled is the length of the trajectory.

Speed

Speed is the rate at which a body changes its position. Average speed is the distance travelled divided by the time taken: average speed = distance travelled / time taken = s/t. Instantaneous speed is the speed of a moving object at a particular moment.