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Energy: Forms and Changes. 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. - PowerPoint PPT Presentation
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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
