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EnergyEnergy
Kinetic and potentialKinetic and potential
Forms of EnergyForms of Energy
MechanicalMechanical - energy with which moving - energy with which moving objects perform work Ex: bicycle, soundobjects perform work Ex: bicycle, sound
ChemicalChemical - energy stored in substances - energy stored in substances because of their chemical makeup Ex: because of their chemical makeup Ex: coal, oil, gasoline, foodscoal, oil, gasoline, foods
Nuclear EnergyNuclear Energy - stored in the nucleus of - stored in the nucleus of the atom Ex: splitting or fusing the atomthe atom Ex: splitting or fusing the atom
Heat EnergyHeat Energy - energy produced by - energy produced by molecular motion Ex: All molecules vibratemolecular motion Ex: All molecules vibrate
Forms of EnergyForms of Energy
ElectricalElectrical - energy as a flow of electrons - energy as a flow of electrons through a conductor, such as a wire Ex: through a conductor, such as a wire Ex: computers, television, appliancescomputers, television, appliances
Light (Electromagnetic)Light (Electromagnetic) - form of radiant - form of radiant energy that moves in waves Ex: solar energy that moves in waves Ex: solar panelspanels
Conservation of Matter and EnergyConservation of Matter and Energy - - energy and matter cannot be created or energy and matter cannot be created or destroyed, only destroyed, only transformedtransformed
Work Work
WorkWork - a form of mechanical energy - a form of mechanical energy always measured in Joules (J)always measured in Joules (J)
Work FormulaWork Formula Work = Force x distanceWork = Force x distance
W = F x dW = F x d Units Joules Newtons meters Units Joules Newtons meters
PowerPower
PowerPower - the amount of work completed in an - the amount of work completed in an specific amount of time, units are specific amount of time, units are WattsWatts
Power FormulaPower Formula Power = Work / timePower = Work / time P = W / tP = W / tUnits Watts = Joules / secondUnits Watts = Joules / second
***See sample problems***See sample problems
Daily Quiz #2 Sm 2Daily Quiz #2 Sm 2 1. What type of energy refers to the movement of an 1. What type of energy refers to the movement of an
object?object? 2. Which type of energy is often referred to as 2. Which type of energy is often referred to as
stored energy?stored energy? 3. Which type of energy is calculated by multiplying 3. Which type of energy is calculated by multiplying
the force of an object by the distance it moved?the force of an object by the distance it moved? 4. What are the units for energy?4. What are the units for energy? 5. What are the units for power?5. What are the units for power? 6. Power is calculated by dividing Work by what?6. Power is calculated by dividing Work by what? Bonus : Which burns more calories running or Bonus : Which burns more calories running or
walking a mile?walking a mile?
MachinesMachines
A machine is a device to make work A machine is a device to make work easier.easier.
Machines do this by changing the size or Machines do this by changing the size or the direction of the applied force.the direction of the applied force.
The force that is applied to a machine is The force that is applied to a machine is called the called the effort forceeffort force, f, fEE. .
The work done on a machine is called The work done on a machine is called work input, Wwork input, Wii
Work must always be done on a machine Work must always be done on a machine if the machine is to do any work. if the machine is to do any work.
The distance through which the machine The distance through which the machine moves is the moves is the effort distanceeffort distance, d, dEE..
WWii = F = FEE X d X dEE
The force applied by the machine is called The force applied by the machine is called the resistance force, Fthe resistance force, FR.R.
The resistance force is often the weight of The resistance force is often the weight of the object being moved. It opposes the the object being moved. It opposes the effort force.effort force.
The distance the object moves is the The distance the object moves is the resistance distance, dresistance distance, dR.R.
Machines can only multiply force. Machines can only multiply force. Because machines cannot multiply work, Because machines cannot multiply work, work output can never be greater than work output can never be greater than work input.work input.
Mechanical AdvantageMechanical Advantage is the number of is the number of times a machine multiplies the effort force.times a machine multiplies the effort force.
EfficiencyEfficiency is the comparison of the work is the comparison of the work output to work input. It is usually output to work input. It is usually expressed as a percent.expressed as a percent.
Efficiency = WEfficiency = WOO X 100 X 100
WWII
Ex) What is the efficiency of a machine that Ex) What is the efficiency of a machine that Has a work output of 200 J and a work Has a work output of 200 J and a work input of 100 J?input of 100 J?
Efficiency = 200 J X 100 = 200 %Efficiency = 200 J X 100 = 200 %
100 J100 J
High efficiency means that much of the work High efficiency means that much of the work is changed to useful work output.is changed to useful work output.
The less friction in a machine the higher the The less friction in a machine the higher the efficiency. efficiency.
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
PE = mghPE = mgh
m = mass in kilogramsm = mass in kilogramsg = acceleration due to gravityg = acceleration due to gravity (9.8 m/s(9.8 m/s22))h = height in metersh = height in metersPotential Energy is measured inPotential Energy is measured in kg kg •• m/s m/s22 •• m = m =
newton meter = newton meter = JoulesJoules
Example 1:Example 1:
If the boulder has If the boulder has a mass of 8kg, a mass of 8kg, and distance B is and distance B is 10m, what is the 10m, what is the potential energy potential energy of the boulder of the boulder relative to the relative to the plateau?plateau?
8kg
10m
Answer:Answer:
PE = mghPE = mgh= 8kg = 8kg • 9.8m/s• 9.8m/s22 • 10m • 10m==784 J784 J
8kg
10m
Example 2:Example 2:
If distance A is If distance A is 20m, what is the 20m, what is the potential energy potential energy of the boulder of the boulder relative to the relative to the bottom?bottom?
8kg
20m
Answer:Answer:
PE = mghPE = mgh= 8kg = 8kg • 9.8m/s• 9.8m/s22 • 20m • 20m== 1568 J 1568 J
8kg
20m
Example 3Example 3
When work is done to stretch something, it When work is done to stretch something, it is called elastic potential energy.is called elastic potential energy.
Find the elastic potential energy stored in a drawn bow if it takes an average force of 100N to pull the arrow back a distance of 0.5 meters.
Answer:Answer:
PE = mgh = FdPE = mgh = Fd
Fxd = 100N x 0.5m= 50J
Kinetic energyKinetic energy
Energy of motionEnergy of motion KE = ½ mvKE = ½ mv22
KE = 1/2mvKE = 1/2mv22
m = mass in kilogramsm = mass in kilogramsv = velocity in meters/secv = velocity in meters/secKinetic energy is measured inKinetic energy is measured in kg kg • m/s • m/s =• m/s • m/s = kg m/skg m/s22 • m = • m = newton meter =newton meter = JoulesJoules
Example 4Example 4
The bird has a mass of 2 kg. It is The bird has a mass of 2 kg. It is flying at a speed of 5 m/s. Find its flying at a speed of 5 m/s. Find its kinetic energy.kinetic energy.
KE = ½ mvKE = ½ mv22
= ½ = ½ • 2kg • (5m/s)• 2kg • (5m/s)22
= ½ • 2kg • 25 m= ½ • 2kg • 25 m22/s/s22
= = 25 joules25 joules
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
How is mass related to How is mass related to energy?energy?
Albert gave Albert gave us the us the answer!answer!
E=mc2
E=mcE=mc22
E = energy in joulesE = energy in joules m = mass in kilogramsm = mass in kilograms c = speed of lightc = speed of light (3 x 10(3 x 1088 m/s) m/s)
A small mass gives a great A small mass gives a great amount of energyamount of energy
Nuclear energy- clean Nuclear energy- clean power for the world?power for the world?
Example:Example:
How much energy can be given off How much energy can be given off by 5 grams of mass? ( 10 paper by 5 grams of mass? ( 10 paper clips = 5 g)clips = 5 g)
5g = 0.005 kg5g = 0.005 kg E=mcE=mc22
= 0.005kg x (3 x 10= 0.005kg x (3 x 1088 m/s) m/s)22
= 0.005 kg x 9 x 10= 0.005 kg x 9 x 101616 m m22/s/s22
= 0.045 x 10= 0.045 x 101616 = 450,000,000,000,000 J= 450,000,000,000,000 J
WOW!!!WOW!!! 450,000,000,000,000 J is the 450,000,000,000,000 J is the amount of energy in 3 amount of energy in 3 million gallons of gasoline!million gallons of gasoline!
