Vocab
1st Law of Thermodynamics
The change in thermal energy of an object is equal to the heat added to the object minus the work done by the object
(ΔU = Q – W)
- ΔU: Change in internal energy
- Q: Heat added to system
- W: Work done by system
What is +/- when work is done BY a system and when work is done ON a system?
- Work done BY system: +
- Work done ON system: -
Converting Kelvin to Celsius
0C = K − 273.15
K = 0C + 273.15
Radiation
- Heat transfer via electromagnetic waves
Example: Fire
Buoyant Force
- The upward force a fluid exerts on an object submerged in it
- Buoyant force of an object submerged = weight of fluid displaced
- Buoyant force of an object floating = weight of object
2nd Law of Thermodynamics
Heat always moves from hotter objects to colder objects unless energy in some form is supplied to reverse the direction of heat flow
Thermal Energy
The combined kinetic energy of all of the molecules in a system
(K = 1/2mv^2)
- K: Kinetic Energy in J
- M: Mass in kg
- V: Velocity in m/s
Heat
- HEAT is the transfer of thermal energy between systems at different temperatures
- Heat (Q) is measured in Joules (J)
- Described as the flow of energy from higher temperature to lower temperature
Pascals Principle
Fluid pushes outward uniformly in all directions when compressed
Specific Heat
- The amount of heat energy needed to raise 1 kg of a substance by 1°C (or 1 K)
- Measured in J/kg*K
- Specific heat can also be represented by c
- Q=mc(Tf - Ti)
Entropy
- The inherent randomness of a system
- Hotter things have higher entropy than colder things
- Heat transfer increases entropy (solid to liquid to gas)
Temperature
A measure of the AVERAGE molecular kinetic energy of an object
(Low temperature objects have lower average molecular kinetic energy and vice versa)
Thermal Equilibrium
- Thermal energy will transfer until the objects have the same temperature
- At this point, heat will no longer occur
Archimedes’ Principle
When you put something in water, the water pushes it upwards
How does a boat float?
A boat floats because the upward buoyant force from the water balances its weight
Heat of Fusion
The amount of energy needed to melt 1 kg of a substance
Why do you get cold when you get out of a pool?
- The hottest molecules have the most energy and can escape by evaporation out into the atmosphere
- You are left with the coldest molecules
Conduction
- Heat transfer through TOUCH
Example: Touching a hot stove
Bernoulli’s Principle
Fast moving fluids have low pressure while slow moving fluids have high pressure
Heat of Vaporization
The amount of thermal energy needed to vaporize 1 kg of a liquid
Temperature Scales
- SI unit for Temperature: Kelvin (K) is based off of ABSOLUTE ZERO
- Temperature in US: Fahrenheit (°F) is based off of the freezing point of an ammonium chloride brine solution
- Celsius is also commonly used, but in more casual everyday instances (°C) and sets zero degrees at the freezing point of water and 100 degrees at the boiling point
Convection
- Heat transfer through the movement of fluids (liquids or gases)
- Heat moves because fluids move
Example: Boiling Water
Pressure
- Measured in Pa
- A lot of force on a smaller area means higher pressure