“Physics for FUTURE LEADERS”Prof. Paul Steinhardt

PLEASE DO NOT SIT IN THE LAST 8 ROWS

Physics 115

Princeton in the Nation’s ServiceWoodrow Wilson, 1896

TAKE OUT A-B-C-D SHEETS

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

John GarciaFrantzesca BarronCaleb VisserGlenna GalarionAshira ShiraliMichael RamirezMenelik Graham*Hunter Sporn*Josiah Gouker*Philip SobocinskiiAatmik Gupta*Julie FangZyan WynnJake Mayer*Mark AgostinelliLaetitia DerroughReis WhiteRonnie Kihonge

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

TCpmQ =

heat energy

mass temperature

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

Example:water: Cp = 1 Cal / kg oKcopper: Cp = 0.09 Cal/kg oK

Heat Capacity & Specific Heat

Which requires more energy to raise 1 degree, water or copper? A) water or B) copper or C) not enuf info

Imagine water and copper both at 50 C. Furthermore, both have the same mass m

(but different Cp)How much heat energy does the water have?

Ans: Q1 = m Cp (273 + 50 ) K.

Now suppose you have added enough heat to raise its T by 1 degree. Now how much energy does it have?

Ans. Q2 = m Cp (273+50+1) K.

How much heat did we have to add?

Q2-Q1= m Cp (1). So which requires more energy?

Did it make a difference if I used K or C?

water: Cp = 1 Cal / kg oKcopper: Cp = 0.09 Cal/kg oK

Some specific heats

Water 1 Cal/kg°C (or °K)Methyl alcohol 0.58 Cal/kg°CAluminum 0.25 Cal/kg°CMarble 0.2 Cal/kg°CGold 0.03 Cal/kg°CApples 0.87 Cal/kg°CDates 0.2 Cal/kg°CStyrofoam 0.35 Cal/kg°CCopper 0.09 Cal/kg°CIron 0.12 Cal/kg°C

If I heat up copper and iron at the same rate,which gets hotter faster?

Heat is a form of kinetic energy

…T is PROPORTIONAL TO the average kinetic energy (½mv2) of atoms and molecules.

(What does 0 oK correspond to?)

typical velocity ~ 1000 ft/sec ~ 330 m/s ~ 800 mi/hr~ speed of sound

speed of light ~ 186,000 mi/sec ~3 x 108 m/s

330 m/s is roughly the speed of what object discussed in class already?

How much heat energy is therein ordinary objects?

Each atom in a ball at room temperature is moving randomly at the speed of soundin air, about . . .1000 ft/s ~ 330 m/s ~ 800 mi/hr. This is about the same speed as a bullet.

How many Cal/gm did the bullet have?

A) .01 Cal/gm B) 1.5 Cal/gm. C) 6 Cal/gm. D) Not enough info

Suppose I throw a (very cold) baseball at 800 mi/hr.A baseball is about 150 gm.

How many Cal’s of kinetic energy have I added to the ball?A) 0.01 Cal B) 1.5 Cal C) 6 Cal D) Not Enuf Info

Suppose all that energy is converted by frictionInto heating the ball when caught in the catcher’s glove

How much will the temperature of the very cold ball increase?A)A few degrees B) 300 KC) 10000 K D) Not Enuf Info

Suppose I throw a (very cold) baseball at 1,600 mi/hr

How many Cal’s of energy have I added to the ball?A) 1.5 Cal B) 3 Cal C) 6 Cal D) Not Enuf Info

Suppose I throw a baseball at 1,600 mi/hr

If that energy were converted to heat energy,what temperature would the very cold ball reach?A) 300 K B) 600 K C) 1200 K D) Not Enuf Info

Suppose I catch the cold baseball moving at 16,000 mi/hr

If I convert that to heat energy, what is the heat energy added to the ball ?

A) 6 Cal B) 60 Cal C) 600 Cal D) 6000 Cal

Suppose I throw a baseball at 16,000 mi/hr

If I convert that to heat energy, about what is the temperature the ball ?

A) 3000 K B) 1200 K C) 12000 K D) 120000 K

They say:The asteroid that hit the Earth became hotter than

the Sun before it hit the ground.

How could it end up hotter than the Sun?