“Physics for FUTURE LEADERS”Prof. Paul Steinhardt

PLEASE DO NOT SIT IN LAST 8 ROWS

Labs begin tomorrowRead IntroToLab Before Coming

HAND IN POST-CLASS HW AT THE BACK OF THE ROOM

BEFORE YOU SIT DOWN

Physics 115

Simons Foundation and Princeton Gravity Initiative Program onF O R E F R O N T S O F G R A V I T A T I O N A L P H Y S I C S

p r e s e n t s

The Dawn of Gravitational Wave Astronomy

A New Window on the Universe

Beverly Berger, StanfordIntroduction by Joseph H. Taylor, Jr

P U B L I C L E C T U R ESeptember 24, 2019 | 7:00pm | McDonnell Hall A01

10 extra credit HW points

+ 5 if you bring a friend not in the class

There are many forms of energyand you can convert one form of energy

into another

THREE KEY FACTS ABOUT ENERGY:

Total Energy is conserved

In any conversion,some stored/kinetic energy

is turned into heat… but you cannot revert back 100%

You consume food energy at about the rate of 100 W.You produce energy at the rate of about 100 W.

As a citizen of the 21st century,at what rate do you use energy of all types?

need to include all the energy that is used for you to support your life – the energy that runs your lights, your computer, that powers the cars and trucks that supply your food; the tractors and other vehicles needed to farm your food; the pesticides and fertilizers; the energy to cook that food; to refrigerate it. Some of you fly or drive to come to campus at the beginning of the year; you are responsible for some share of all the buildings on campus here to support your lifestyle; the lawnmowers that cut the grass and all that…

10,000 W

You consume energy at about the rate of 100 W.You produce energy at the rate of about 100 W.

As a citizen of the 21st century,at what rate do you use energy?

(A) 10 W(B) 100 W(C) 1000 W(D) 10,000 W

From R. Wolfson, Energy Environment and Climate (Norton Pub, 2012)

#1 uranium-235 20,000,000 Cal

#2 asteroid 107 Cal

#3 hydrogen (fuel cells) 26 Cal

#4 propane 13 Cal

#5 gasoline 10 Cal

#6 butter 7 Cal

#7 Snickers 5 Cal

#8 TNT 0.65 Cal

#9 computer battery 0.1 Cal

#10 bullet, flashlight battery 0.01 Cal

for1 gram: What do these have in common?

#1 uranium-235 20,000,000 Cal

#2 asteroid 107 Cal

#3 hydrogen (fuel cells) 26 Cal

#4 propane 13 Cal

#5 gasoline 10 Cal

#6 butter 7 Cal

#7 Snickers 5 Cal

#8 TNT 0.65 Cal

#9 computer battery 0.1 Cal

#10 bullet, flashlight battery 0.01 Cal

for1 gram: What do these have in common?

#1 uranium-235 20,000,000 Cal

#2 asteroid 107 Cal

#3 hydrogen (fuel cells) 26 Cal

#4 propane 13 Cal

#5 gasoline 10 Cal

#6 butter 7 Cal

#7 Snickers 5 Cal

#8 TNT 0.65 Cal

#9 computer battery 0.1 Cal

#10 bullet, flashlight battery 0.01 Cal

for1 gram:

What does this suggest aboutenergy needs for exploring

space: Man vs. robots?

2. Atoms & Heat

Energy

Ability to do workAnything that can be turned into heat

Recall:

à HEAT IS A FORM OF ENERGY

What do you think?

Are HEAT and TEMPERATURE the same thing?

Let’s ask ourselves some questions:If I increase the temperature of an object,

do I increase its heat energy?

If I double the temperature of an object, do I double its heat (energy)?

Do two objects at the same temperature havethe same amount of heat energy?

Do HEAT and TEMPERATURE have the same units?

A) Yes B) No C) I don’t know

3259 += CF

273+=CK

zeroabsoluteK Û= 0

1st Law of Thermodynamics• Heat is a form of energy

(1 Calorie ~ 4 kilojoules)

• The amount of energy is proportionalto the temperature

• Energy (including heat) is conserved

0th Law of Thermodynamics:

Objects in contact reach same T

TCpmQ =

heat energy

mass temperature

specific heat: the value of Cp depends on the substance.

Heat Capacity & Specific Heat

If I increase the temperature of an object, do I increase its heat energy?

If I double the temperature of an object, do I double its heat (energy)? (are units important?)

Do two objects at the same temperature have the same amount of heat energy?

Do HEAT and TEMPERATURE have the same units?

THERMAL IMAGING

Things that are hot give off light

0° 100°

50°

Start with equal amounts of water at 0°C and 100°C…

… combine them ...

… resulting in water at 50°.

Combination of 0th and 1st laws

0° 100°

33°

Now start with twice as much water at 0º as 100º….

… combine them ...

… resulting in water at 33°.

What if the second beaker contained alcohol?