The rope ladder of a boat hangs over the side of
the boat and just touches the water. The
ladder rungs are 8 inches apart. How many
rungs will be under the water when the tide
rises 3.5 feet?
A. 1 rung
B. 2 rungs
C. 5 rungs
D. 0 rungs
How much heat would need
to be added to a 2.5 kg
sample of water in order to
increase the temperature
from 35oC to 95oC? (Remember Q
= mcΔT) cwater = 4190 J/kgoC
A. 366.6 kJ
B. 628.5 kJ
C. 995.1 kJ
D. 1361.8 kj
Because the rubber ball’s
temperature increased faster
than the banana dipped in LN2,
that means which had a higher
specific heat.
A. The rubber ball
B. The banana
C. Both have the same
D. Neither are capable for getting heat
Pre-AP Physics Unit 5:
Thermodynamics
“Thermodynamics”
Is derived from Greek meaning “movement of heat.”
The First Law of Thermodynamics
Official Definition:
When heat flows in or out of a system, the energy it
gains or loses is equal to the amount of heat transferred.
Or… Heat = Energy !
Is analogous to the Law of Conservation of Energy
We are now dealing with Internal Energy
Temperature:
What is it?
How “Hot” or “Cold” a substance is.
Temperature represents the average
translational kinetic energy of the individual
particles in a system.
The Temperature Scales
Fahrenheit – water freezes at 32oF and boils at 212oF
Celsius – Water freezes at 0oC and boils
at 100oC
Kelvin – is based off of Absolute Zero
Absolute Zero
So cold that all particles stop moving!
Total energy of the particles is 0.
Temperature:
Temperature Conversions
Celsius to Fahrenheit
9
𝑇𝐹 = 𝑇𝐶 + 32
5
Fahrenheit to Celsius
5
𝑇𝐶 = (𝑇𝐹 − 32)
9
Celsius to Kelvin
Examples
𝑇𝐾 = 𝑇𝐶 + 273
A piece of metal is heated to 475 oF,
what is this temperature in Celsius?
A. 887 oC
B. 246 oC
C. 519 oC
D. -27 oC
The melting point of copper is
1073 oC. What is this
temperature in Kelvin?
A. 800 K
B. 1899 K
C. 578 K
D. 1346 K
Specific Heat Capacity
What is it?
The resistance to change in temperature of a substance.
The Equation:
Q = mcΔT
Examples:
How much heat energy is
required in order to raise the
temperature of a 0.5 kg iron nail
from a temperature of 25oC to
80oC?
A. 5750 J
B. 18400 J
C. 12650 J
D. 24150 J
A 75 kg piece of a concrete
sidewalk on a sunny day will gain
about 650,000 Joules of heat
energy from the sun. By how
much will its temperature
increase on that day?
A. 25133333 K
B. 3.0 K
C. 16810 K
D. .33 K
An iron pot containing 5 kg of water at
an initial temperature of 23oC is placed
on a stove. If the stove applies 560,000
Joules of heat energy, what is the final
temperature of the water?
A. 49.7 oC
B. 26.7 oC
C. 3.7
oC
D. 76.5 oC
A cup of water (c=4190) and a
piece of metal (c=350) are both
left to sit out on a sunny day. By
the end of the day, which will
have a greater change in
temperature?
A. water
B. metal
C. They will have same temperature
D. I don’t know
The Second Law of
Thermodynamics
Official Definition:
Heat, of itself, never flows from a colder object to a
warmer object.
Energy always flows from Hot to Cold
This law is also called the Law of Entropy
What is Entropy?
The amount of disorder in a system
The universe is always moving towards more entropy
Examples:
Ice melting
Liquid water evaporating
It takes Work (energy) to decrease Entropy
Types of Heat Transfer
Conduction
Heat transfer between materials that are in direct contact
with each other.
Convection
Transfer in a fluid by movement of the substance itself.
Radiation
Energy transmitted by electromagnetic waves.
Phase Changes
The States of Matter:
Phase Changes
Types of Phase Changes:
Melting
Melting
Boiling
Evaporation
Evaporation
Condensation
Boiling
Sublimation
Condensation
Sublimation
Phase Changes
How do you change the melting point or boiling point of
a substance?
Add a solute
Change the pressure
Phase Changes
Energy During Phase Changes
What happens to the temperature of water as heat is
added?
It Increases.
What happens to the temperature during a phase change?
It remains constant.
Phase Changes
Latent Heat
Latent Heat of Fusion
The amount of energy required to change a unit mass of any
substance from a solid to a liquid (and vice versa).
Abbreviated Lf (or Hf )
Latent Heat of Vaporization
The amount of energy required to change a unit mass from
liquid to gas (and vice versa).
Abbreviated Lv (or Hv)
Lf
Lv
Phase Changes
Latent Heat
Equation:
Q = mL
Where:
Q = heat added during phase change
m = mass of sample
L = Latent Heat (of fusion or vaporization)
Examples:
How much heat is required to boil 3.5
kg of water? (Lv = 2.26x106 J/kg)
A. 7910 J
B. .0001264 J
C. .0000001264 J
D. 7910000J
An experiment is performed and
it is found that it takes 13.0 x 106
Joules of energy to melt 4.8 kg of
iron. What is the Latent Heat of
fusion for Iron?
A. 2.7 x 106 J/kg
B. 2.7 x 103 J/kg
C. 6.2 x 107 J/kg
D. 6.2 x 104 J/kg
Latent Heat of Fusion
Lf
0
