Energy Transfer Review

Energy Categories

• Energy can be divided into two main categories:

  • Kinetic Energy: Energy of motion.

  • Potential Energy: Energy stored in an object due to its position.

Potential Energy Transformation

• The potential energy stored in a rock at the top of a cliff:

  • Increases as the rock is lifted.

  • Decreases as the rock falls towards the earth due to gravitational force.

Energy Transformations in Devices

• Electric Hair Dryer:

  • Energy transformation that takes place is:

  • Electrical energy $\rightarrow$ Heat energy + Kinetic energy (from the fan).

Types of Stored Energy

• Battery Energy: The kind of energy stored in a battery is chemical energy.

Temperature Measurement

• Device Used: The device used to measure temperature is a thermometer.

Heat Transfer Concepts

• Lizard on a Heating Rock:

  • Direction of heat transfer: From the rock to the lizard.

  • Type of heat transfer occurring: Conduction.

• As the temperature of a material increases, the kinetic energy of the particles increases.

• Definition of Heat:

  • Heat is the transfer of thermal energy from areas that are warmer to areas that are cooler.

• Temperature and Kinetic Energy:

  • Temperature is the average kinetic energy of the particles of an object and does NOT depend on the mass of the object.

Thermal Energy Explanation

• Thermal Energy Definition:

  • Thermal energy is the total kinetic energy trapped in an object which depends on the mass, temperature, and state of the object.

Freezing of Water

• Cause of Freezing: When water is put in the freezer, the cooling air removes heat from the water, causing it to freeze.

Cold Sensation

• When you go outside and it is cold out, you feel “cold” because:

  • Heat is rapidly escaping from your body to the colder environment.

Water Freezing and Boiling Points

• Freezing Point of Water: Water freezes at 0°C (32°F).

• Boiling Point of Water: Water boils at 100°C (212°F).

• Absolute Zero: The temperature of absolute zero is -273.15°C (0 K).

Thermal Conductivity in Insulation

• For the insulated box challenge, the materials that would do the best to slow down heat transfer by conduction are:

  • Materials with low thermal conductivity.

Kinetic Energy during Freezing

• As water freezes, the kinetic energy of the water molecules decreases.

Sensation of Heat

• Touching a Hot Cup of Coffee: You feel hot when you touch a hot cup of coffee due to:

  • Heat transfer from the cup (which is at a higher temperature) to your skin (at a lower temperature).

Heat Transfer in Water

• When ice is added to a warm glass of water, the heat from the warm water goes to the ice cube melting the ice cube and making the water cooler.

Insulation in Homes

• Material Used: Insulation is typically placed in between the walls of a home to keep heat from escaping.

Heat Transfer Direction in Homes

• Summer: In your house, heat transfers from the outside (warm air) into the home because the inside is cooler.

• Winter: In the wintertime, heat transfers from inside (warm air) out to the colder outside air.

Gravitational Potential Energy (GPE)

• In the context of gravitational potential energy, the ball with the greatest gravitational potential energy is the one at the highest position.

Energy Conservation

• According to the Law of Conservation of Energy, the energy in a system:

  • Cannot be created or destroyed, only transformed from one form to another.

Energy Efficiency

• Energy efficiency of a machine is never 100% due to:

  • Losses to heat and other forms of energy dissipation.

Types of Heat Transfer

• The type of heat transfer that allows the sun’s electromagnetic heat energy to travel through the vacuum of space is radiation.

• The type of heat transfer that helps distribute heat within a house is convection.