Thermal Energy & Work Flashcards
What is a steam engine and why was it developed?
- Any machine generating steam, converting the pressure into mechanical motion
- Deeper coal mines needed and built, take water out of
Who were the three people (in order) who built and improved the steam engine?
- Thomas Savery
- Thomas Newcomen (+cylinder and piston)
- James Watt (+double acting piston, separate condenser)
What were the consequences of the steam engine?
The Industrial Revolution
What was Empedolces’ Theory of the Elements
- All matter was composed of a combination of four elements (Water, Air, Earth, Fire)
- Objects contained fire and as they burned the fire was released
(Eventually there were too many new substances that couldn’t be classified)
What was the Phlogiston Theory?
- Substances that could burn contained an invisible substance, phlogiston
- When they were burned, phlogiston flowed out, and the substance got lighter
- This theory is flawed because some objects gain mass as they burn
What was the Caloric Theory?
- Caloric (heat) was a massless and invisible fluid found in all substances and could flow from one object to another
- Caloric always flowed from warm objects to cool objects
- Black defined “calories”, which was the amount of caloric (heat) that would increase the temperature of 1g of water by 1° C
- Disproved since heat is not a fluid. According to this, it has to come from somewhere, but when you rub your hands together, it generates infinite heat
What is the modern theory of heat?
- First by Benjamin Thompson or Count von Rumford
- Heat is energy
- It was ignored because caloric could explain how heat could travel in a vacuum
- Also, by Robert Mayer, who was separate: heat is related to energy
- O2 is used to provide energy, and must also provide heat
- Finally, James Joule was given the credit of discovering the mechanical equivalent of heat
What is energy and kinetic energy? What are the units of energy and kinetic energy?
The ability to do work, and the energy of motion.
Joule (J)
What are the formulas and units to calculate force?
F = ma, where m = mass (kg), a = acceleration (m/s^2)
If a is due to gravity or falling, use g = 9.81 m/s^2
Force is in Newtons. It is a vector.
What is work?
Transfer in mechanical energy from one object to another. In Joules. W = ΔE.
Scalar
What are the conditions for work to be done on a specific object?
- There must be a change in displacement
- The object must move in the same direction as the force
Energy must change!
- The force must be applied to the object
What are the three formulas for work?
W (J) = F (N) x d (m)
W = ma (because F = ma) x d (m)
W = m (mass, kg) x g (a = g) x h (height = distance = meters)
What are the units for work and force?
J = Nm, N = kgm/s^2
How to calculate the work in a F x d graph?
Work is the area between the line on a F vs d graph, and the x-axis
How did Joule’s apparatus that showed that heat and work were equivalent work?
As a weight falls, it pulls a string and causes the drum and paddles to rotate.
The water heats up as it is stirred.
The paddles do work on the water, and give it energy in the form of heat. Joule determined that 4.16J of work done on water caused an increase of 1 degree Celsius in temperature in 1g of water.
