Energy: Forms and Changes

Energy: Energy: Forms and Forms and ChangesChanges

Nature of Energy

Energy is all around you!You can hear energy as sound.You can see energy as light.And you can feel it as wind.

Nature of Energy

Energy is the ability to do work or

bring about change.

Nature of Energy

What is energy that it can be involved in so many different activities?Energy can be defined as the

ability to do work.If an object or organism does

work (exerts a force over a distance to move an object) the object or organism uses energy.

Nature of Energy

Because of the direct connection between energy and work, energy is measured in the same unit as work: joules (J).

In addition to using energy to do work, objects gain energy because work is being done on them.

Forms of Energy

The five main forms of energy are:ThermalChemicalElectromagneticNuclearMechanical

Heat Energy The molecular motion of

the atoms is called thermal energy, because moving particles produce heat.

Thermal energy can be produced by friction.

Thermal energy causes changes in temperature and phase of any form of matter.

Chemical Energy

Chemical energy is required to bond atoms together.

And when bonds are broken, energy is released.

Chemical Energy

Fuel and food are forms of stored chemical energy.

Electromagnetic Energy

Power lines carry electromagnetic energy into your home in the form of electricity.

Electromagnetic Energy

Light is a form of electromagnetic energy.

Each color of light (Roy G Biv) represents a different amount of electromagnetic energy.

Electromagnetic Energy is also carried by X-rays, radio waves, and laser light.

Nuclear Energy

The nucleus of an atom is the source of nuclear energy.

Nuclear Energy

When the nucleus splits—fission— nuclear energy is released in the form of thermal energy and EM energy.

Nuclear energy is also released when nuclei collide at high speeds and undergo fusion

Nuclear EnergyThe sun’s energy is produced from nuclear fusion in which hydrogen nuclei fuse to form helium nuclei.

Nuclear Energy

Nuclear energy is the most concentrated form of energy.

Mechanical Energy

When work is done to an object, it acquires energy. The energy it acquires is known as mechanical energy.

Mechanical Energy

When you kick a football, you give mechanical energy to the football to make it move.

Mechanical Energy

When you throw a bowling ball, you give it energy. When that bowling ball hits the pins, some of the energy is transferred to the pins.

Energy Conversion

Energy can be changed from one form to another. Changes in the form of energy are called energy conversions or energy transformations.

Thermal and Kinetic

Electrical

Energy conversions

All forms of energy can be converted into other forms. The sun’s energy through solar cells

can be converted directly into electricity.

Green plants convert the sun’s energy (electromagnetic) into starches and sugars (chemical energy).

Other energy conversions

In an electric motor, electromagnetic energy is converted to mechanical energy.

In a battery, chemical energy is converted into electromagnetic energy.

The mechanical energy of a waterfall is converted to electrical energy in a generator.

Energy Conversions

In an automobile engine, fuel is burned to convert chemical energy into thermal energy. The thermal energy is then changed into mechanical energy.

Chemical Heat Mechanical

States of Energy

The most common energy conversion is the conversion between potential and kinetic energy.

All forms of energy can be in either of two states: Potential Kinetic

States of Energy: Kinetic and Potential Energy

Kinetic Energy is the energy of motion.

Potential Energy is stored energy.

Kinetic and Potential EnergyKinetic and Potential Energy

Energy can be classified as Energy can be classified as potential or kineticpotential or kinetic

Potential energy: energy of positionPotential energy: energy of position

The boulder hasmore gravitationalpotential energy whenmeasured from point A compared to B.

PE = mgh

Kinetic and potential energy Kinetic and potential energy conversionsconversions

Describe the energy Describe the energy conversions in this picture:conversions in this picture:

At the top: At the top: ¼ of the way down:¼ of the way down:½ way down:½ way down:¾ down¾ downAt the bottom:At the bottom: Is the sum of KE + PE a Is the sum of KE + PE a

constant?constant?

All PE, no KE

3/4 PE, 1/4 KE

1/2 PE, 1/2 KE

1/4 PE, 3/4 KE

No PE, All KE

Yes! It’s always10,000 J in this case.

Where are PE and KE maximums Where are PE and KE maximums in this picture?in this picture?

What happens when the cord is cut?

Potential energyis converted tokinetic energy!

Kinetic and potential energy Kinetic and potential energy convert to one anotherconvert to one another

KE max KE max

no PE no PE

PE maxno KE

PE max

no KE

Kinetic Energy

The energy of motion is called kinetic energy.

The faster an object moves, the more kinetic energy it has.

The greater the mass of a moving object, the more kinetic energy it has.

Kinetic energy depends on both mass and velocity.

Potential Energy

Potential Energy is stored energy.Stored chemically in fuel, the

nucleus of atom, and in foods.Or stored because of the work

done on it:Stretching a rubber band.Winding a watch.Pulling back on a bow’s arrow.Lifting a brick high in the air.

Gravitational Potential Energy

Potential energy that is dependent on height is called gravitational potential energy.

Gravitational Potential Energy

If you stand on a 3-meter diving board, you have 3 times the G.P.E, than you had on a 1-meter diving board.

Gravitational Potential Energy

A waterfall, a suspension bridge, and a falling snowflake all have gravitational potential energy.

Elastic Potential Energy

Energy that is stored due to being stretched or compressed is called elastic potential energy.

Gravitational Potential Energy

“The bigger they are the harder they fall” is not just a saying. It’s true. Objects with more mass have greater G.P.E.

The formula to find G.P.E. isGPE = mgh

Kinetic-Potential Energy Conversion

Roller coasters work because of the energy that is built into the system. Initially, the cars are pulled mechanically up the tallest hill, giving them a great deal of potential energy. From that point, the conversion between potential and kinetic energy powers the cars throughout the entire ride.

Kinetic vs. Potential Energy

At the point of maximum potential energy, the car has minimum kinetic energy.

There is a constant trade off between KE and PE that equals total ME.

Kinetic-Potential Energy Conversions

As a basketball player throws the ball into the air, various energy conversions take place.

Ball slows down Ball speeds up

The Law of Conservation of Energy

Energy can neither be created nor destroyed by ordinary means. It can only be converted from one form

to another. If energy seems to disappear, then

scientists look for it – leading to many important discoveries.

Thermodynamics

Cartoon courtesy ofNearingZero.net

TEMPERATURE, HEAT AND THERMAL

ENERGY

Temperature & Heat

Temperature Temperature is related to the average kinetic energy of the particles in a substance.

Temperature

Temperaturemeasure of the

average KE of the particles in a sample of matter

Thermal Energy

Thermal Energythe total energy of the particles

in a materialKE - movement of particlesPE - forces within or between

particles due to positiondepends on temperature, mass,

and type of substance

SI unit for temp. is the KelvinKelvin

a. K = C + 273 (10C = 283K)

b. C = K – 273 (10K = -263C)

Thermal Energy – the total of all the kinetic and potential energy of all the particles in a substance.

Thermal Energy

Which beaker of water has more thermal energy?B - same temperature, more mass

200 mL

80ºC

A400 mL

80ºC

B

Thermal energy relationships

a. As temperature increases, so does thermal energy (because the kinetic energy of the particles increased).

b. Even if the temperature doesn’t change, the thermal energy in a more massive substance is higher (because it is a total measure of energy).

Heat

a. The flow of thermal energy from one object to another. b. Heat always flows from warmer to cooler objects. Ice gets

warmer while hand gets

cooler

Cup gets cooler while hand gets

warmer

Why does A feel hot and B feel cold?

80ºC

A

10ºC

B

Heat flows from A to your hand = hot.

Heat flows from your hand to B =

cold.

We know that thermal energy can be transformed or transferred. Now let’s look at just how thermal energy is transferred.

Heat is transferred by conduction, convection or radiation.

Conductionheat is transferred by particles touching and transferring kinetic energy to those they touch

the closer the particles (i.e. solids) the better the conduction

both atoms and free electrons can jiggle and jostle and keep the heat transfer going

Convection is the transfer of heat by the movement of the material--gas or liquid particles

Currents are formed at the source of the heat and causes the heated material to rise through the fluid, carrying the heat with it

As the fluid cools, it falls and the process begins again

Radiation heat is transferred in

matter or space by means of electromagnetic waves that carry energy

waves carrying radiant energy are absorbed by objects and transfer kinetic—thermal—energy to the objects they enter

Specific Heat

Some things heat up or cool down faster than others.

Land heats up and cools down faster than water. Why?

Heat Transfer Units

Like work, heat is...measured in joules (J) HOWEVER

you will still see it in calories as well

1cal = 4.186 Ja transfer of energy

The amount of heat required to raise the temperature of one gram of substance by one degree Celsius.

Specific Heat

Why does water have such a high specific heat?

Water molecules form strong bonds with each other; therefore it takes more heat energy to break them. Metals have weak bonds

and do not need as much energy to break them.

water metal

C. Heat Transfer

Specific Heat (Cp)amount of energy required to raise the temp. of 1 kg of material by 1 degree Kelvin

units: various!!!!!!!!!

So check the units in the problem!!!!!

C. Heat Transfer Which sample will

take longer to heat to 100°C?

50 g Al 50 g Cu

• Al - It has a higher specific heat.• Al will also take longer to cool down.

C. Heat Transfer: Doing the Math

Q = m Cp T

Q: heat (J)m: mass (kg)T: change in temperature (K or °C)Cp: specific heat (J/kg·K)

T = Tf - Ti– Q = heat loss+ Q = heat gain

C. Heat Transfer A 32-g silver spoon cools from 60°C to 20°C.

How much heat is lost by the spoon?

GIVEN:

m = 32 g

Ti = 60°C

Tf = 20°C

Q = ?

Cp = 235 J/kg·K

WORK:

Q = m·T·Cp

m = 32 g = 0.032 kg

T = 20°C - 60°C = – 40°C

Q = (0.032kg)(-40°C)(235J/kg·K)Q = – 301 J

C. Heat Transfer How much heat is required to warm 230 g of

water from 12°C to 90°C?

GIVEN:

m = 230 g

Ti = 12°C

Tf = 90°C

Q = ?

Cp= 4184 J/kg·K

WORK:

Q = m·T·Cp

m = 230 g = 0.23 kg

T = 90°C - 12°C = 78°C

Q = (0.23kg)(78°C)(4184 J/kg·K)Q = 75,061 J

A Bomb Calorimeter

Calorimeter is Used to Measure Heat

A Cheaper Calorimeter