Warm-up: 1. What is the kinetic energy of a charging rhino that has a mass of 1500 kg and a velocity of 5 m/s? 2. What is the potential energy of a 2 kg.

Warm-upWarm-up11 What is the kinetic energy of a What is the kinetic energy of a

charging rhino that has a mass charging rhino that has a mass of 1500 kg and a velocity of 5 of 1500 kg and a velocity of 5 msms

22 What is the potential energy of What is the potential energy of a 2 kg water balloon held off of a 2 kg water balloon held off of an 80 m tall buildingan 80 m tall building

33 Is it possible for one object to Is it possible for one object to have both KE and PE at the have both KE and PE at the same time If so give an same time If so give an exampleexample

A quick recaphellipA quick recaphellip

EnergyEnergy is is possessedpossessed by an object by an object

WorkWork is done when energy is is done when energy is transferredtransferred from one object to from one object to anotheranother

In other words In other words workwork is a measurement is a measurement of how much energy was of how much energy was gainedgained or or lostlost by an objectby an object

Energy transferred into workEnergy transferred into work

When would W = KEWhen would W = KE

When would W = PEWhen would W = PE

Example 1Example 1A 1 kg soccer ball reaches a maximum A 1 kg soccer ball reaches a maximum height of 30 m after a goaliersquos drop kick height of 30 m after a goaliersquos drop kick How much How much workwork could the ball do on a could the ball do on a midfielderrsquos headmidfielderrsquos headW = PEW = PE (the (the workwork it can do is equal to its it can do is equal to its energyenergy) )

W = mgh W = mgh

= (1kg)(10ms= (1kg)(10ms22)(30m) )(30m)

= 300J= 300J

When a certain car locks up the brakes and slides When a certain car locks up the brakes and slides it has a frictional stopping force of 2500 N If the it has a frictional stopping force of 2500 N If the car has a mass of 1000 kg how far will the car car has a mass of 1000 kg how far will the car slide if it slams on the brakes traveling at 10 msslide if it slams on the brakes traveling at 10 ms

W = KE W = KE (the brakes have to do work to stop the carrsquos KE) (the brakes have to do work to stop the carrsquos KE)

FFd = frac12 mvd = frac12 mv22

(2500N) d = (12)(1000kg)(10ms)(2500N) d = (12)(1000kg)(10ms)22

2500 kgms2500 kgms22 d = 50000 kgm d = 50000 kgm22ss22

d = 20md = 20m

Example 2Example 2

Practice problemshellipPractice problemshellipA car smashes into a stationary cow while traveling at 10 ms A car smashes into a stationary cow while traveling at 10 ms and does 62500 J of work on the cow How much mass does and does 62500 J of work on the cow How much mass does the car havethe car have

W = KE (the work the car can do is equal to its KE)W = KE (the work the car can do is equal to its KE)

62500J = frac12mv62500J = frac12mv22

62500kgm62500kgm22ss22 = frac12 m(10 ms) = frac12 m(10 ms)22

m = 1250kgm = 1250kgA baseball catcher applies 640 N of force to stop the incoming A baseball catcher applies 640 N of force to stop the incoming fastballs thrown by his pitcher When the pitcher throws a fastballs thrown by his pitcher When the pitcher throws a fastball it knocks the catcherrsquos glove back 25 m before fastball it knocks the catcherrsquos glove back 25 m before completely stopping the ball If a baseball hascompletely stopping the ball If a baseball has a mass of 2 kg a mass of 2 kg how fast is the pitcherrsquos fastballhow fast is the pitcherrsquos fastball W = KE W = KE (the work required to stop the ball is equal to its KE)(the work required to stop the ball is equal to its KE)

FFd = frac12mvd = frac12mv22

v = 40 msv = 40 ms

Internal EnergyInternal EnergyDefinitionDefinition energy due to the random energy due to the random motion of molecules motion of molecules

Also called ldquothermal energyrdquo becauseAlso called ldquothermal energyrdquo becauseHighHigh temperature = large internal energy temperature = large internal energy

LowLow temperature = small internal energy temperature = small internal energy

Even ice at Even ice at 00 C C has a fairly large amount has a fairly large amount of internal energyof internal energy

Zero internal energy = Zero internal energy = -273-273 C C (this is (this is ldquoabsolute zerordquo - the lowest possible ldquoabsolute zerordquo - the lowest possible temperature)temperature)

Internal energy is a Internal energy is a combinationcombination of of KE and PE on a microscopic scale KE and PE on a microscopic scale which makes it impossible for us to which makes it impossible for us to measure individuallyhellipwe need to measure individuallyhellipwe need to use temperature as an indicator of use temperature as an indicator of internal energyinternal energy

ldquoldquoColdColdrdquo is simply the absence of rdquo is simply the absence of internal energyinternal energy

ColdCold cannot flow cannot flow intointo something something you can only you can only remove energyremove energy from it from it to lower its temperatureto lower its temperature

Example A refrigerator doesnrsquot put Example A refrigerator doesnrsquot put coldness coldness intointo the food it the food it removesremoves energy from the foodenergy from the food

HeatHeatDefinitionDefinition a transfer of energy that results in a a transfer of energy that results in a change in temperature change in temperature HeatHeat is another measurement of energy so it is another measurement of energy so it has units of Jouleshas units of JoulesJust like we said with Work an object cannot Just like we said with Work an object cannot containcontain heatheat Instead we say that heat is ldquotransferredrdquo Instead we say that heat is ldquotransferredrdquo whenever there is a temperature changewhenever there is a temperature changeHeatHeat always flows from an object with higher internal always flows from an object with higher internal energy to something with less internal energyenergy to something with less internal energyldquoldquoAn object An object hashas energy an object can energy an object can dodo work An work An object object hashas energy an object can energy an object can transfertransfer heatrdquo heatrdquo

(Biological Energy)(Biological Energy)

Application ProblemsApplication Problems1) How many times would you have to lift a 10 pound weight 1) How many times would you have to lift a 10 pound weight

(equivalent to about 50 N of force) through a distance of 1 m (equivalent to about 50 N of force) through a distance of 1 m in order to burn 1 Calorie (1Cal = 4186 J)in order to burn 1 Calorie (1Cal = 4186 J)

(about 84 times)(about 84 times)2) How many Calories did you burn in the Harvard Step 2) How many Calories did you burn in the Harvard Step

Test Test (your work4186 J)(your work4186 J)

3) How many minutes would you have to keep stepping in 3) How many minutes would you have to keep stepping in order to burn off a 280 Calorie Snickers bar order to burn off a 280 Calorie Snickers bar

(280 Calabove answer)(280 Calabove answer)This would be pretty bad news if we had to burn all our This would be pretty bad news if we had to burn all our

Calories by doing mechanical work What are some other Calories by doing mechanical work What are some other ways that our bodies use energy ways that our bodies use energy (Think about the fact that our body temperature is (Think about the fact that our body temperature is maintained at 986 degrees)maintained at 986 degrees)

Human MetabolismHuman MetabolismEven when inactive an average adult male has a Even when inactive an average adult male has a basal metabolism rate of basal metabolism rate of 90 W90 W That means he That means he burns over burns over 1850 Cal1850 Cal per day just by being alive per day just by being alive

Calculating Basal Metabolic Rate (BMR)Calculating Basal Metabolic Rate (BMR)(Enter pounds inches and years into your equation)(Enter pounds inches and years into your equation)

Males 66 + (623W) + (127H) - (68A) = CaldayMales 66 + (623W) + (127H) - (68A) = Calday

Females 655 + (435W) + (47H) ndash (47A)Females 655 + (435W) + (47H) ndash (47A)

Multiplication FactorsMultiplication Factors12 ndash little or no exercise12 ndash little or no exercise1375 ndash (light exercise 1-3 days per week)1375 ndash (light exercise 1-3 days per week)155 ndash (moderate exercise 3-5 days per week)155 ndash (moderate exercise 3-5 days per week)1725 ndash (heavy exercise 6-7 days per week)1725 ndash (heavy exercise 6-7 days per week)

The Biological ProcessThe Biological ProcessWhenever fats carbs or proteins enter our Whenever fats carbs or proteins enter our body they are broken down into the body they are broken down into the chemical chemical glucoseglucose Everything else gets Everything else gets dumped to the large intestine for dumped to the large intestine for eliminationeliminationGlucoseGlucose is the ldquogreatest common is the ldquogreatest common denominatorrdquo of biological energydenominatorrdquo of biological energyWhenever we do not use all of the energy Whenever we do not use all of the energy that we have consumed our body builds the that we have consumed our body builds the extra glucose into fat because fat is the extra glucose into fat because fat is the most efficient means of storing energymost efficient means of storing energyIf the bodyrsquos extra energy was stored as If the bodyrsquos extra energy was stored as carbs instead of fat then ldquocelluliterdquo would carbs instead of fat then ldquocelluliterdquo would take up 3 to 4 times as much space as it does take up 3 to 4 times as much space as it does now (hellipbut it would also burn off at a now (hellipbut it would also burn off at a faster rate)faster rate)

Nutrition and CaloriesNutrition and Calories

Carbs 1g = 4 CaloriesCarbs 1g = 4 Calories

Fat 1g = 9 CaloriesFat 1g = 9 Calories

Protein 1g = 4 CaloriesProtein 1g = 4 Calories