Investigation #5

The Kinetic Energy of MoleculesThe Kinetic Energy of Molecules

During the school day there was a great deal of discussion about the hurricane that was approaching the east coast of the U.S. Over the night and into the next day the storm raged across the Delmarva Peninsula, though weakened by making landfall in North Carolina it was still very powerful. As everyone went back to school the next day, students noticed that roads had been damaged by the water and that several trees had been knocked over.

Hurricanes are an excellent example of extraordinary amounts of GPE and KE.

Where do hurricanes get their energy?

Hurricane facts• Total Energy stored in actions of air/rain

= 5.2 x 1019 Joules/day

• This is equivalent to 200 times the world-wide electrical generating capacity!

• Just wind: 1.3 x 1017 Joules/day

For strong storms the wind works on…

• The water, creating a storm surge, similar to a continuous tsunami

• The storm surge for Katrina max out at 27.8 feet

Hurricanes and energy• Some of this energy takes the form of

GPE of the huge quantities of water droplets that make the clouds of the hurricane.

• Imagine GPE stored in the mass of water in a ‘puddle’ that is a foot deep and covers the entire State of Delaware, lifted a mile or so up in the air

KE and Hurricanes

• Huge quantities of air are propelled at speeds that approach or exceed 100 mi/hr.

• When the hurricane makes landfall, the KE of the air and water is transferred to trees, buildings, power poles, cars, boats, and anything else in the hurricane’s path.

Source of GPE and KE of a Hurricane

• Hurricanes form in the warm waters of the tropics.

• The storms draw their energy from the heat energy stored in these waters

Main goal

• In this activity, you will learn how the KE of tiny particles of matter, called molecules, can be used to explain the heat energy that fuels these storms, the water waves that transfer their fury, and the kinetic energy of their devastating winds.

(Material Adapted from ON THE BALL, Particle Models for Key Stage 3 Science, Royal Society of Chemistry, University of Southhampton,© 2001)

A Review of the Particle Model from middle school

• The Particle Model is used to understand the structure of matter

• We used this model in middle school to help us understand how energy travels through substances.

Main themes of the Particle Model

Theme 1• We learned that particles in liquids and

solids are connected differently, and that the particles that make up a gas are not connected at all.

• These differences help us understand why solids, liquids and gases have different properties.

Theme 2

• The Particle Model helped us understand that heat energy is really the kinetic energy of particles of matter that are too small to see

• Heat energy moves by conduction

through solids, but through convection in liquids and gases.

What is the difference between conduction and

convection?

Theme 3• This model helped us understand that

when objects slide, bounce, or roll to rest, their kinetic energy does not just disappear.

• Kinetic energy of the object is transformed into the random kinetic energy of its (and surrounding) particles; the form of energy we called heat energy.

Theme 4

• The Particle Model was used to explain that the density of a substance tells us how tightly packed its particles are

Theme 5

• The model was used to emphasize the differences between the organized vibrations of particles in matter (mechanical waves) and the random vibrations of particles (heat energy).

Theme 6

• We used the Particle Model to describe how sound and other mechanical waves move through substances, but cannot move through a vacuum.

Vacuum means an area devoid of anything, including air and any other gas.

Key ideas of Kinetic Theory model

Key ideas1. Matter is composed of tiny particles.

2. The particles of a single substance are the same, whether the substance is a solid, liquid or gas. 

3. Only the strength of the connections between particles changes when the phase (state) of the substance changes.

4. Particles are always moving (even in solids).

Key ideas5. Particles in solids move back and forth around a

fixed position.  The extent of their motion is severely limited because of the connections that bind the particles of a solid together, keeps particles closely packed

6. Particles in liquids move more freely than they do solids.  The connections between particles in a liquid are weaker than in a solid, but strong enough to keep the particles close together.

Key ideas7. Particles in gases are not connected to each other or

anything else. They move freely, randomly colliding with each other and bouncing off the walls of their container.

8. Adding energy usually causes the particles in substances to move faster.

9. Adding or subtracting enough energy to particles can cause a change in phase/state

So Far

• In Class we have investigated and explored the energy of objects we can see with our own eyes

• Do particles have energy?

A Better name

• Instead of Particles

• Use Molecules

Definition of a molecule• Molecules are the building blocks of all matter• In gases, the molecules are not connected to each

other in any way.  • Liquids and solids are formed when the molecules bind

together.

In this unit…• We will be taking a closer look at the forces that bind

molecules to each other and the types of motion the molecules can have because of these binding forces.

• Later in the school year you will be investigating molecules in greater detail.

THE ELECTRIC FORCE – THE BINDING FORCE OF MATTER

• The electric force acts between electric charges.

• Its attractive electric force that binds the molecules to each other.

Electric forces and Bending

• These electric bonds are stronger in some materials than others, but the molecules are never rigidly bound together.

• This is why all materials can bend and stretch

Investigating Water MoleculesInvestigating Water Molecules

Focus Question: How can water droplets be used to provide evidence of the flexibility of molecular bonds?

What was your journal entry?

Creating the water droplet on the penny.

Analyzing the interaction of one water drop onto the water bubble

Notice the flexibility of the water molecule bonding.

Does it behave like tiny springs?

Water molecule bonds are flexible …

Investigation Reflection• Question #1: Solids, like sand, will pile-up when

poured on a flat surface, but the grains will slide down the sides of the pile. How is the pile of water different from a pile of sand?

• Question #2: What evidence from this last step of the investigation can you give to support the statement that water molecules are linked together by attractive binding forces?

• Question #3: What evidence can you give that the binding forces that link the water molecules create flexible spring-like bonds?

Investigating Oscillations Produced by Elastic MaterialsInvestigating Oscillations Produced by Elastic Materials

Pre-Investigation Questions

• Question #4: Using the graph, determine how long the mass moves back and forth before finally coming to rest.

• Question #5: How many times did the mass oscillate back and forth before coming to rest (each complete back and forth motion is called a cycle)?

• Question #6: Why do you think the mass comes to rest? Where does the kinetic energy of the block go?

Investigation Reflection• Question #7: How much time is needed to complete

one cycle (back and forth motion of the mass)? (This time period is called a period.)

• Question #8: How long does it take for the moving mass to come to rest?

• Question #9: You determined which of the elastic materials had the largest or smallest elastic constants (k) earlier in the unit. Does the size of the elastic constant of the rubber bands, bungee cord and spring help determine how the mass will oscillate?

Using Models to Analyze Molecular Bonding

How can sphere and spring models be used to analyze energy transfer on

the molecular level?

Demonstrating a collision using the molecular model

Key Ideas:Key Ideas:

A trampoline is another good model to illustrate molecular

bonding. Notice how the surface of the trampoline is changed by

the person jumping on it.

Image Source: John Lambert Pearson, www.flickr.com

Investigating Vibrations in Solids (Part A)Investigating Vibrations in Solids (Part A)

Why are the vibrations in solids important?

Investigating Vibrations in Solids (Part B)Investigating Vibrations in Solids (Part B)

Focus Question: How can the vibration signature of a solid enable us to describe the flexibility of the molecular bonds in the substance?

Investigation Reflection• Question #10: Why does the force detected by the sensor oscillate?

• Question #11: How do the vibrations change when the golf ball is dropped from more than 50cm, say 100cm for instance? Are there any characteristics of the vibration signature that stay the same?

• Question #11: How do the vibration signatures change if something besides a golf ball is dropped on the tabletop? Are there any characteristics of the vibration signature that stay the same?

• Question #12: How do the vibration signatures change when the ball is dropped onto different surfaces (wood, a textbook, a piece of rigid foam, etc.)?

Analyzing Organized and Disorganized Forms of Energy

How does knowledge about molecular bonding help us better understand thermal

energy (heat energy)?

Thermal Energy• Molecules are almost never at rest, they are in

constant motion in a random, disorganized manner.

• The total amount of the molecular KE is called Thermal Energy.

• Thermal energy is difficult to quantify, but the temperature of an object tells us the average KE of the molecules.

• Scientists misunderstood thermal energy (heat energy) in the beginning. They thought heat was a fluid-like substance and didn’t realize that it was actually energy until much later.

Investigating the Random Nature of Thermal EnergyInvestigating the Random Nature of Thermal Energy

In this investigation you will observe how food coloring moves in three beakers, each having a different thermal energy.

Pre-Investigation Questions

1. What will happen if a small metal ball is dropped into a beaker of water? Why?

2. What will happen if a drop of liquid food coloring is dropped into a beaker of water? Why?

3. Will the temperature of the water affect either result? In what way?

Experiment Results

Hot Water Room Temp Water Cold Water

Investigation Reflection1. What happened to the color drop as it fell

through the water?

2. Did the temperature of the water have any effect on the results? If so, what effect?

3. Predict what is likely to happen to the color after an hour. Explain your reasoning.

4. How can your observations be used to explain the particle nature of matter?

Where Does Heat Energy Come From?

• Heat energy (thermal energy) is typically the end result of an energy chain. Other forms of energy are usually transformed into heat energy.

• Heat energy can be transferred by conduction or convection. It can also be transformed into an EM energy and transferred to something else (heat energy transfer by radiation).

• The forces of friction and air resistance commonly transform the KE of moving objects into thermal energy.

• Heat energy is not a very useful form of energy because of its random nature. This is the reason for the poor efficiencies of cars and electric power plants.