Physical Science Applications in Agriculture

UnitPhysical Science Systems

Problem Area

Agricultural Structural Systems

Specific Heat

Lesson

Warming Up!

• Place a stack of fifteen pennies and a stack of nickels equal in height on a metal pan.

• Put the pan on a hot plate and turn the plate onto its lowest setting.

• Put your forefingers on the top of the coin stacks and ask the students if one stack of coins will feel warmer faster that the other or will both feel warm at the same time.

Learning Objectives

1. Explain the Kinetic Molecular Theory.2. Describe the three mechanisms of heat

transfer.3. Identify the sources of thermal energy.4. Justify the advantage of solids

compared to liquids or gases as a conductor.

Terms

• Calorimeter• Conduction• Convection• Gas• Kinetic-Molecular

Theory• Latent heat

• Law of Thermodynamics

• Liquid• Radiation• Solid• Specific heat• Temperature

What is the Kinetic Molecular Theory?

• Kinetic theory is based on the idea that particles of matter are always in motion and that this motion has consequences.

• The kinetic theory applies to solids, liquids, and gases.

water.me.vccs.edu/concepts/pressure.html

What is the Kinetic Molecular Theory?

A. Kinetic-Molecular Theory provides an explanation for heat and temperature.

• Matter is composed of particles called molecules (atoms) which are in continuous motion.

• Heat results from the motion of the molecules

What is the Kinetic Molecular Theory?

B. The kinetic molecule theory explains the forces between molecules and the energy that they possess.

www.anatomy.usyd.edu.au/.../eyeball%20images

This theory has 3 basic assumptions.

1. Matter is composed of small particles (molecules).

2. The measure of space that the molecules occupy (volume) is derived from the space in between the molecules and not the space the molecules contain themselves.

3. The molecules are in constant motion.

This motion is different for the 3 states of matter.

a. Solid—molecules are held close to each other by their attractions of charge.– They will bend and/or vibrate, but will stay

in close proximity.b. Liquid—molecules will flow or glide over one

another, but stay toward the bottom of the container.– Motion is a bit more random than that of a

solid.

This motion is different for the 3 states of matter.

c. Gas—molecules are the continual straight line motion.

– The kinetic energy of the molecule is greater than the attractive force between them, thus they are much farther apart and move freely of each other.

What is the Kinetic Molecular Theory?

C. When the molecules collide with each other, or with the walls of a container, there is no loss of energy. – Heat results from the motion of these

molecules.D. Temperature is a measure of the average

kinetic energy of the molecules of a substance.– As molecules move faster the

temperature of a substance increases.

What are the three mechanisms of heat transfer?

• The three mechanisms of heat transfer are conduction, convection, and radiation.

www.keidel.com/design/select/ovens-convection.htm

Conduction

• Transfer of heat by direct contact. • Simplest method of heat transfer.• A metal pan put directly above a hot

burner is heated by conduction.1. Which is a better conductor, tinfoil or

Styrofoam? 2. What are other examples of conduction?

Convection

• Transfer of heat by movement of the heated part of a gas or liquid.1. Heat transfer by convection can take

place only in gases or liquids.2. When a gas such as air or a liquid such

as water is heated unevenly, the heated part rises. This is an example of convection

Radiation• Transfer of heat through space by infrared

rays. • This heat transfer does not cause particles

of matter to move.1. The earth receives heat energy from the sun

by radiation. 2. You feel warm while sitting in the sun

because you are receiving heat from the sun by radiation.

What are the sources of thermal energy?

• Temperature is a description of a condition, a measure of the average kinetic energy of the particles in a sample matter.

• Temperature indicates how hot or how cold something is.

• The greater the kinetic energy of the particles in a sample of matter, the higher the temperature of the matter is.

What are the sources of thermal energy?

• Heat is the sum total of the kinetic energies of the particles in a sample of matter.

• Heat always flows spontaneously from matter at a higher temperature to matter at a lower temperature.

What are the sources of thermal energy?

• To illustrate the difference between temperature and heat, consider a bathtub full of warm water and a cup of boiling water.1. The temperature of the water in the tub is

lower than that of the water in the cup.2. Although the kinetic energy of each

particle in the cup is greater than that of each particle in the tub, the total heat energy in the tub will be much greater than that in the cup, which has few particles.

What are the sources of thermal energy?

• Law of Thermodynamics—heat may not be created or destroyed; it will result from the conversion of another form of energy.

• When two bodies are in contact, heat will flow from a warm body to a cold body until they are at equal temperatures.

What are the sources of thermal energy?

• The heat required to raising one pound of substance one degree Fahrenheit or one gram of a substance one degree Celsius is known as specific heat.

1. Materials vary in their ability to absorb and exchange heat.

2. This information is important to know when choosing materials for internal combustion engine components.

3. Heat must be contained and dissipated during operation.

SPECIFIC HEAT FORMULA

specific heat of a sample =

heat loss from the samplemass x temperature change

What are the sources of thermal energy?

• Latent heat is the amount of heat needed to bring about a change of state.

• About 80 calories of latent heat are needed to change one gram of ice at zero degrees Celsius to water at zero degrees Celsius.

What are the sources of thermal energy?

• Calorimetry deals with losses and gains of heat.

• A calorimeter is used to measure the amount of heat lost by an object through transfer to a liquid, generally water.

Calorimeter1. The calorimeter is specially designed so that

minimum of heat is lost to its surroundings.• Heat gain or loss is reflected in a change of

temperature.2. The amount of heat needed to raise the

temperature of a substance a certain amount when compared to the amount of heat needed to raise an equal amount of water the same number of degrees is called specific heat.

3. A calorie is the amount of heat need to raise one gram of water one degree Celsius.

Calorimeter

Why are solids generally better conductors than liquids or gases?

• Solids are generally better conductors than liquids or gases because the molecules are closer together.

A. Most metals, such as aluminum and copper, are good heat conductors.

B. Other materials, such as wool, straw, paper, cork, and wood are not good conductors of heat.

C. This is because most metallic elements are denser than cork, wood, or other non-conductors, hence the molecules are even closer together.

Review/Summary

• What is the Kinetic Molecular Theory?• What are the three mechanisms of heat

transfer? • What are the sources of thermal energy?• Why are solids generally better conductors

than liquids or gases?