Chapter 4 Physics Flashcards
Thermodynamics
the field of physics that deals with forces and motion involving the transfer of thermal energy
First Law of Thermodynamics
Energy cannot be created nor destroyed but can be transformed from one form to another or transferred from one object to another
Second Law of Thermodynamics
No process is 100% efficient in converting energy into work (some energy will always be converted to thermal energy due to friction)
Thermal energy always flows from object at a ______ temperature to objects at a ______ temperature
higher, lower
Empedocles
all matter consists of four elements; earth, air, fire, and water (when objects burn fire is released)
Phlogiston
substances that could burn contained an invisible fluid called “phlogiston” (flowed out of objects when burned)
Caloric Theory
•“Caloric” was thought to be a massless fluid found in all matter
•It cannot be created not destroyed but can flow from warmer objects to cooler objects
•The term “calorie” is still used today (1 cal. Increases temperature of 1g of water by 1 degree
The Count Rumford Hypothesis
•Notice cannon barrels get hot
•Mechanical energy can be converted to heat = heat is equivalent to energy
Julius Robert Mayer
•Found evidence supporting Rumford
•Recognized the body uses oxygen to break down food and use it for energy
James Prescott Joules
Discovered that mechanical energy is equivalent to heat (unit of energy = Joule)
Kinetic Molecular Theory
•Atoms are in random motion and collide with each other, transferring energy and doing work
•Work and energy are related, both measured in Joules
Kinetic Energy
the energy of motion
Kinetic-molecular energy
energy of atoms and molecules in constant random motion (thermal energy)
Heat
the transfer of thermal energy from one object to another
Temperature
Average kinetic energy of the atoms or molecules in a substance
Specific Heat Capacity
the amount of energy (J) to increase the temperature of 1g of the substance by 1 degree (Unit: J/g°C)
Specific Heat Capacity of Water
•Water molecules form strong hydrogen bonds with each other
•Lots of kinetic energy is needed for water molecules to break away from each other
Specific Heat Capacity Formula
Q=mcΔT
Heat of Fusion
Q= nHfus (energy needed to melt or freeze a substance)
Heat of Vaporization
Q= nHvap (energy needed to vaporize or condense a substance)
Physics of Work
•Work is done when a force acting on an object changes the position or condition of the object
•Work is the transfer of mechanical energy from one object to another
•Measured in Joules, which are equivalent to Nm
Calculating Work
W= fΔd
Negative Work
when force is applied in the opposite direction of the motion
Position vs. Force Graphs
•Show the relationship between Force and change in position
•Length is the force
•Width is the distance
•Rectangle: A= l • W
•Triangle: A= 1/2 b • h
•Non-uniform shapes: calculated by finding the area of one square on the grid then multiplying it by the number of squares
Interal Combustion Engines
- The fuel goes directly into the cylinder (intake stroke) (intake valve opens)
- Combustion occurs inside the cylinder (compression stroke) (both intake and exhust valves close)
- The hot gases expand and push the piston down the cylinder (power stroke) (both valves are still closed)
- When the pressure and/or volume of a gas increases, the gas does work (exhust stroke) (exhust valve opens)
Steam Engines
“external combustion engines”, fuel is burned outside the engine and is used to generate steam in a boiler (steam drives the pistons)
Production of Electrical Energy
thermo-electric generating stations first produce heat, which used to convert water into steam in large boilers. The steam turns turbines connected to larger generators
