Science UNIT 3

Heat and the Environment

• Understanding heat and energy in relation to the environment.

What is Energy

• Definition of energy as the ability to do work and make objects move.

• Overview of the different types of energy and how they move through the world.

• Connection between energy and particle theory.

• Exploration of how energy and heat impact our environment.

Energy and its Types

Types of Energy

• Thermal Energy: Energy of moving particles.

• Chemical Energy: Energy stored in matter, particularly in chemical bonds.

• Magnetic Energy: Energy that attracts or repels certain metals.

• Gravitational Energy: Energy stored due to position above the ground.

• Nuclear Energy: Energy stored at the center of particles.

• Elastic Energy: Energy stored in stretched, compressed, bent, or twisted objects.

• Light Energy: Energy that can be detected by our eyes.

• Electrical Energy: Energy of charged particles in motion.

• Sound Energy: Energy produced from vibrations that we can hear.

• Mechanical Energy: Energy of objects in motion.

Forms of Energy in Use

• Mechanics of Daily Activities:

  • Kicking a ball involves mechanical energy.

  • Using a lamp engages light energy for reading.

  • Nuclear power plants produce nuclear energy.

  • Eating an apple converts chemical energy to mechanical energy.

  • Listening to music utilizes sound energy.

The Law of Conservation of Energy

• Energy cannot be created or destroyed but can be transformed or transferred.

Energy Transfer vs Energy Transformation

• Energy Transfer: Movement of energy from one object to another.

  • Example: Mechanical energy from a leg is transferred to a ball when kicking it.

• Energy Transformation: Change of energy from one form to another.

  • Example: Electrical energy from wires is transformed into light energy by a light bulb.

Examples of Energy Transfer

• Kicking a ball:

  • Mechanical energy moves from the leg to the ball.

• Charging a phone:

  • Electrical energy moves from a socket to the phone.

• Heating soup:

  • Thermal energy moves from a stove to the pot to the soup.

Examples of Energy Transformation

• Dropping a ball:

  • Converts gravitational energy to mechanical energy.

• Turning on a light:

  • Converts electrical energy to light and thermal energy.

• Using a fridge:

  • Transforms electrical energy to thermal energy.

• Eating an apple:

  • Transforms chemical energy to mechanical energy.

• Snapping an elastic:

  • Converts elastic energy to mechanical energy.

• Listening to the radio:

  • Transforms electrical energy to sound energy.

. 2

Heat and the Environment

• Understanding the key concepts of heat and energy.

What is Heat?

• Defining Heat: Heat involves understanding the difference between heat, temperature, and thermal energy.

Temperature, Heat, and Thermal Energy Comparison

• Temperature, heat, and thermal energy seem similar but denote different concepts:

  • Temperature: A measure of the average kinetic energy of particles in a substance.

  • Heat: The transfer of thermal energy.

  • Thermal Energy: A measure of the total kinetic energy of all particles in a substance.

Temperature

• Definition: Temperature is quantified using a thermometer. It reflects the average kinetic energy of all particles in a solid, liquid, or gas.

Measuring Temperature

• Common temperature scales include:

  • Celsius (°C): Water boils at 100°C, freezes at 0°C.

  • Fahrenheit (°F): Water boils at 212°F, freezes at 32°F.

  • Kelvin (K): Water boils at 373 K, freezes at 273 K.

  • Body Temperature examples: 37°C, 98.6°F, 310 K.

  • Notes:

    • Celsius and Kelvin are widely used in science, while Fahrenheit is primarily used in the USA.

    • Fun Fact: Mr. Fahrenheit miscalculated body temperature for his scale.

    • Absolute zero is 0 K; Outer space temperature is approximately 2.7 K (-270°C).

Thermal Energy

• Definition: Thermal energy is the measure of the total kinetic energy of all particles in a substance (solid, liquid, gas).

Difference Between Temperature and Thermal Energy

• Thermal vs Temperature:

  • Total thermal energy considers all particles (e.g., a pot of room temperature water might have more thermal energy than a cup of boiling water due to a higher number of particles).

  • Average temperature is based on the kinetic energy of particles (e.g., the cup of boiling water has a higher average temperature).

Heat

• Definition: Heat is the transfer of thermal energy from one object to another.

• Transfer Conditions: Heat transfer continues until thermal equilibrium is reached (i.e., objects have equal thermal energy).

  • Heat travels from areas of higher thermal energy to areas of lower thermal energy:

    • Example transfers:

      • From mug to hands.

      • From fire to air to hands.

      • From flame to pot to water.

• Solid

  • Defined shape and volume.

  • Particles are closely packed and vibrate in place.

• Liquid

  • Defined volume but no defined shape.

  • Particles are close but can move past each other, allowing liquids to flow.

• Gas

  • No defined shape or volume.

  • Particles are far apart and move freely at high speeds.

Phase Changes

• Adding or Removing Thermal Energy

  • Change in Speed of Particles: Increasing thermal energy causes particles to move faster, while decreasing thermal energy causes them to slow down.

• Phase Transitions

  • Melting: Solid to liquid (adding thermal energy)

  • Freezing: Liquid to solid (removing thermal energy)

  • Evaporation: Liquid to gas (adding thermal energy)

  • Condensation: Gas to liquid (removing thermal energy)

  • Sublimation: Solid to gas (adding thermal energy)

  • Deposition: Gas to solid (removing thermal energy)

Energy Transfer in Phase Changes

• Increasing Thermal Energy:

  • When energy is added (e.g., heating), particles speed up and change from solid to liquid (melting) or from liquid to gas (evaporation).

• Decreasing Thermal Energy:

  • When energy is removed (e.g., cooling), particles slow down and change from gas to liquid (condensation) or from liquid to solid (freezing).

Descriptive Scenario

• Situation with Tight Lid:

  • As gas particles inside a container with a tight lid are heated, they gain thermal energy and increase speed, causing an increase in pressure until the lid may pop off.

• Situation with Wilted Balloons:

  • Balloons lose gas over time. As gas escapes, the thermal energy decreases, leading to a reduction in pressure and volume, resulting in the balloons appearing wilted.

Unit 3: Heat in the Environment

3.3 Heat Transfer

Overview of Heat Transfer

• Heat transfer occurs when energy is carried through or across one solid, liquid, or gas to another object.

Types of Heat Transfer

1. Conduction

• Transfer of heat through a solid or between solids, liquids, and gases.

• Not all materials conduct heat equally; properties of materials affect heat conduction efficiency.

• Conductors: materials that transfer heat well (e.g., metals).

• Insulators: materials that do not transfer heat well (e.g., wood).

2. Convection

• Transfer of thermal energy in fluids (liquids and gases).

• Process of convection:

  • Step 1: Heat is transferred from the heating element to the particles at the bottom.

  • Step 2: Particles at the bottom vibrate quickly, gaining energy.

  • Step 3: Heated particles push upwards, causing cooler particles to move to the side.

  • Step 4: Cool particles sink to the bottom, and the cycle repeats.

3. Radiation

• Transfer of energy by invisible waves emitted by a heat source.

• Example: Thermal energy from the sun reaches the Earth by radiation.

• Infrared Waves: All hot solids, liquids, and gases emit invisible heat waves.

• When radiant energy contacts a solid, the particles absorb the energy, resulting in them vibrating more and heating up.

• Dark-colored objects absorb more radiant energy than light-colored objects, hence dark objects will feel warmer.

Practical Applications and Observations

• Why does metal feel cooler than wood?

  • Both materials can be at the same temperature, but metal, being a better conductor, allows heat from the hand to transfer faster than wood, making it feel cooler.

• Why does hot air rise and cold air sink?

  • Hot air is less dense than cold air, leading it to rise as cooler, denser particles sink.

• Why are houses painted white in hot climates?

  • White reflects radiant energy, keeping houses cooler compared to darker colors that absorb heat.

• Why are shiny foil blankets used after accidents or for runners?

  • Shiny foil reflects heat back to the body, helping maintain warmth.

Experimentation with Containers

1. Warm Water Containers:

   • After 10 minutes, the shiny metal container keeps water warmest as it reflects heat, while the dull black container absorbs heat.

2. Distance from Heater:

   • The dull black container will heat up the most after 10 minutes due to absorption of radiant energy, while shiny metal will be coolest as it reflects radiation.