8 th grade energy unit. what is energy? energy – the ability to do work or create a change. –law...

8TH GRADE ENERGY

UNIT

What is ENERGY?

• ENERGY – The ability to do work or create a change.– Law of Conservation: Energy is

neither created nor destroyed…only changes form & position.

• WORK – Force exerted on an object (matter) that causes it to move…energy is needed!

• W : force x distance moved = ____joules

Kinetic Energy

• Kinetic Energy (KE) – The energy of an object due to its motion.

• How to find kinetic energy:

KE: Mass of object x Velocity ² ÷ 2 =____Joules

Potential Energy / GPE

• Potential Energy – Energy that is stored and held in readiness.

– Gravitational Potential Energy (GPE) – Potential energy that depends on the height of object from surface.

• GPE: height of object (h) x mass (m) =

LAB Reviews

• Transfer of energy means to pass energy from one place to another (one object to another) without changing forms.

• Transformation of energy means that energy has changed from one form to another.

Ball & Ramp

Less GPE = less speed = less KE

More GPE = higher speed = more KE

GPEKE

GPE

KE

GPEKE

GPE

KE

Passing energy along…

The KE from the ball was transferred (passed) to the Styrofoam cup…the ball lost KE and the cup gained KE…Work was done!! (Cup absorbed the KE from ball)

Transfer & Transformation

GPE KE

KEGPE

TRANSFORMATIONTRANSFORMATION

TRANSFERTRANSFER

•Air particles

•Surface (ramp & floor)

•Cup

Pendulum demonstration

GPEKE

GPEKE

GPEKE

GPE

KE

GPEKE

GPEKE

GPEKE

• Transformation of Energy GPE KE GPE again…

Roller Coaster

‘W’ has the greatest GPE, so ‘X’ will have the greatest KE. The rest of the roller coaster ride will run fine because it has enough initial KE to make it over the rest of the smaller hills.

Energy transfer (absorbed) – activity #5

• How does type of surface affect energy transfer?

– Surfaces whose particles are tightly packed can only absorb a little bit of energy at a time (many bounces)

– Surfaces whose particles are loosely packed can absorb more energy at a time (less bounces)

Bouncing Ball

Flooraccepts less energy at atime… more dense

Cardboard acceptsmore energy at a time…less dense

GPEKE

GPE

KE

Activity #7 (transfer of energy)

KE is transferred from person rope wood.

Activity #7 (transformation of energy

Because of FRICTION between the rope and wood, the KE transformed into heat !!

HOT

Phase Change Particle Model

Low KE medium KE High KE

Phase change names

melting vaporization

freezing condensation

Phases of Matter

• Melting – Phase change from solid to liquid. Increased KE of particles from added energy

• Vaporization – Phase change from liquid to gas. Lots of KE from added energy.

• Condensation – Phase change from gas to liquid. Less KE of particles from loss (transfer) of energy.

• Freezing – Phase change from liquid to solid. Very low KE of particles.

Activity #8 (phase change)

In this activity, energy was added to the ice which caused increased KE and then phase changes. The reason the graph has areas where temperatures don’t rise is because the energy at that point is not used to heat the substance, but rather change the phase…then heating continues.

What is Thermal Energy?

• The TOTAL energy of all the particles that make up a substance (matter).

• 3 Factors to find thermal energy:1. Temp.

2. Amount (mass or volume)

3. Phase (solid, liquid, or gas)

Temperature

• Thermometers measure temperature…

• Temperature measures the “average KE” (motion) of particles that make up a substance.

What is heat ?

• Heat is the actual transfer of Thermal Energy. When Thermal Energy is transferred from one place to another, we call it “heat.”

Thermal energy gets transferred to the air, then to the person (HEAT).

Fire has LOTS of Thermal Energy

Transformation of Energy examples…

• EngineEngine = chemical kinetic

• HeaterHeater = chemical heat

• SolarSolar = radiant electrical

• BatteryBattery = chemical electrical

• FoodFood = chemical heat / KE

• PhotosynthesisPhotosynthesis = radiant chemical

Energy Chains

• Energy can transfer & transform.• This reaction forms “energy chains”,

where we can map out the transfer & transformation of energy. We usually start with the Sun

Phases of Matter

What becomes of KE?

What becomes of KE after it transfers?

• When KE transfers from one place to another through physical contact, it not only gives the energy of motion, but also transforms into heat energy!

• Friction – A resistance between 2 or more particles or objects causes KE to transfer.

Different Temperature Scales

Absolute Zero K: Point at which all motion has stopped…no energy!!

Force

• In order for KE to be transferred or transformed, there must be something making “matter” accelerate or change direction.

• Force = is a push or pull that causes a substance with mass (takes up space) to accelerate in a certain direction.

» Force can change amount of friction!!!

Thermal Expansion & Contraction

• In physics, thermal expansion is the tendency of matter to change in length or volume in response to a change in temperature. When a substance is heated, its particles move around more vigorously and by doing so generally maintain a greater average separation. This requires more space!!

1st Law of Thermodynamics

• States that energy is neither created nor destroyed…it is just passed along and/or transformed (conservation of energyconservation of energy).

– All the energy that is in the universe right now can only change position or form!

2nd Law of Thermodynamics

• Thermal energy flows (heat) spontaneously from a warmer body to a cooler one.

• One cannot transfer or transform heat completely into useful work, some of the energy becomes unusable…

• Every isolated system becomes disordered in time (entropy).

3 ways Thermal Energy transfers (heat)

1. CONDUCTION

2. CONVECTION

3. RADIATION

CONDUCTION

• Process where heat energy is transferred by physical contact through a substance. Particles of a substance have to touch each other to pass heat from warmer to cooler.

Warmer area,Lots of KE

Cooler area,gaining KE…warming up

Collision of particles

Conductor vs. Insulator

• Conductor – A substance that allows heat to transfer through it.

• Insulator – A substance that does NOT allow heat to transfer to the cooler area easily.

Insulators

Fire gear: keeps heat from skin exposure

Space suit keeps heat from sun minimal

Ice actually slows the transfer of heat from inside to outside

CONVECTION

• Transfer of heat by circulation or movement of the hot particles to cooler areas. Warmer, less dense fluids rise, while cooler, more dense fluids fall and replace.

Warm, less dense air rises…cools

Cool, more denseair falls…warms again

RADIATION

• Energy that travels through the emptiness of space…does not need particles to transfer (medium). Travels by electromagnetic waves away from a heat source.

Investigation #11Conduction

• Purpose / Question:– To observe how HEAT energy moves

by conduction.

– Do some substances allow heat energy to conduct better than others?

• Background Knowledge:– Look at the demonstration. Which

spoon would you pick up first?

metal or plastic

– Why?

• Hypothesis:– Rods with more mass will (allow / not

allow) heat to transfer well.

– Rods with less mass will (allow / not allow) heat to transfer well.

• ExperimentMaterials:

– Solid rods (aluminum, steel, brass, glass)– Hollow rods (brass & aluminum) – 2 clothes pins– Candles– Large paper– 2 blocks– Timer – Safety goggles!!!

Procedure

1. Find the mass of each type of rod (g) and record in data table.

2. Be very precise in measurements!

Metal Rod

• 3. Take one rod (save glass rod for last) and line it up on template.

• 4. Using the marker, place a line where the 3 globs of wax will be resting & flame line.– Flame line = 3inches from edge.– Wax 1 = 2 inches from edge.– Wax 2 = 1 inch from edge.– Wax 3 = very edge of rod.

Wax 3Wax 2Wax 1FLAME

ROD

• 5. Light big candle and allow wax to run off and drip onto the designated 3 areas for wax globs (edge, 1in., and 2 in.)

• 6. Use the clothes pins to suspend the bar above the surface.

• 7. stack 2 blocks & place a lit candle directly under the inner-most marked line on bar.

• 8. Once flame hits the bar, start timing.• 9. You are looking for how long it takes

each glob of wax to start melting. • 10. Write observation times in data

table.

Final set-up for Investigation #11

CONDUCTION

• Process where heat energy is transferred by physical contact through a substance. Particles of a substance have to touch each other to pass heat from warmer to cooler.

Warmer area,Lots of KE

Cooler area,gaining KE…warming up

Collision of particles

What is Radiation?

• All energy, typically from a light source like a star (Sun) that transfers energy without a medium (but can transfer some through liquids & gases)

– A medium refers to anything made up of particles (solids, liquids, gases)

Color affects absorption

Black bodies: Summer clothing:  white reflects radiant energy better than black.

 Until equilibrium is reached, white  stripes on roads are at a lower  temperature than black asphalt.

 Wrap an ice-cube in black cloth and another in aluminum foil and  place both in the sunshine.  What will happen?

What are Waves?

• A wave is a disturbance when energy is transferred through a ‘medium’.– Medium is what energy is passing

through (solid, liquid, gas, etc…)

• This disturbance can cause the medium to become displaced– Sometimes permanently – Sometimes temporarily

2 Categories of Waves

• 1.) Mechanical Waves – Energy that requires a “medium” to transfer.

• 2.) Electromagnetic Waves (EM) – Energy that does NOT need a “medium” to transfer

Sound is just vibrations of air particles hitting each other.

Earthquakes send enormous amounts of energy through matter.

Heat & light

Type of Waves

3. Surface Waves – Combinations of transverse & longitudinal waves, causing a circular motion of particles. This occurs between 2 mediums (water & air).

Types of Waves cont…

Transverse Wave – Waves that move the medium at “right angles” to the direction in which the energy is traveling.

The medium Medium being disturbed by the energy

Direction of energy flow

Parts of a Transverse Wave

Frequency (1second time = Hz)

Wavelength (λ)

amplitude

Crest

Trough

Medium

Types of Waves cont…

2. Longitudinal Waves – Waves that moves the particles of the medium “parallel” to the direction the energy is traveling. (SOUND)

Energy

Amplitude

• – maximum displacement of the medium as energy passes.

Crest & Trough

• - The section of the wave that rises above the undisturbed medium is called the crest. The section below is the trough.

Wavelength (λ)

• - The distance between any 2 same points of different waves.

Frequency

• How many wavelengths occur per second.– Hertz (Hz)

SOUND WAVES

Air particles are disturbed back and forth as compression waves.

• Different frequencies = different pitch.

Compression Waves

Speed of Sound

Sound propagates (travels) through gas slower because it is generally less dense.

Sound propagates through liquids faster because they are more dense, can hit each other and pass energy easier

Sound propagates through solids much faster because of the high density…energy transfers easiest.

Sound from stationary source

Sound energy propagates outward (Compression waves) in all directions.

Sound from moving source (Doppler Effect)

• The apparent change in Frequency as the wave source moves toward or away from the listener. Car is source

making noise (moving)Frequency

is lower (low pitch) Frequency

is higher (high pitch)

Click for visual Click for example

Supersonic (breaking sound barrier)

• When a wave source catches up and passes the outgoing waves of energy. Sound barrier

Click for video example

Electromagnetic Radiation(EM Waves)

Energy that is coming from our star (The Sun). We have identified many different types of energy from the Sun and named them.

What are EM radiation waves?

– Space is mostly made of magnetic & electric fields

– EM radiation disturbs the electric and magnetic fields transversely as it passes by.

Differences in EM energy

Different energy from the Sun all travel the same speed through space (186,000 miles/sec)

Energy with longer wavelengths = smaller frequency = less energy

Energy with shorter wavelengths = higher frequency = more energy

Types of EM Radiation

How does energy travel through emptiness of space???

• “Space particles” known as photons carry energy through space, but not matter.

• Some photons carry lots of energy (gamma rays)

• Some photons carry little energy (radio waves)

Visible Light

The part of the Electromagnetic Spectrum (frequency) that our eyes can detect.

Properties of Visible Light

Shorter wavelength = higher frequency

Longer wavelength = lower frequency

Diffraction

• Diffraction is the splitting of light energy to its individual frequencies (colors)

Refraction

As light energy passes through different mediums (solids, liquids, or gases) it slows down to different speeds.

Optical illusion – You see the rod because light is reflecting off of it. The light is reaching your eyes at different speeds because it is passing through different mediums (water, glass, air)

Refraction cont…

The Sun’s light energy is refracted when it enters our Earth’s atmosphere.

Transmission

• To allow light energy to pass through a substance.

TRANSPARENT (clear)

TRANSLUCENT (not clear)

Reflection

• Regular Reflection – When parallel rays of light hit a smooth surface and all the rays bounce off the same direction & angle

bounces

Reflection cont…

• Diffuse Reflection – When parallel rays of light hit a bumpy or uneven surface they bounce off at different angles & direction.

Absorption

• When visible light is absorbed, it is known as the “absence” of light…which is black.

White

All absorbedBlack

How we see

White light from Sun strikes and object

All color frequencies of spectrum absorbed, but this blue

Light: Waves of energy, particles, or both???

Light has NO mass…can pass through substances without increasing mass…acts like a EM wave.

Light sometimes acts as a particle where it reflects or even moves substances…acts like a particle. Light particle is a PHOTON

flashlight

flashlight

Photon carries the energy

Visible Light Hitting an Object

1. Refraction

2. Transmission

3. Scattering

4. Reflection

5. Absorption

Scattering

Scattering – Light can be redirected in many directions when other particles are present…such as gases or liquids.