5.1 thermal physics

• temperature is a measure of hotness of an object on a chosen scale
• thermal equilibrium is when two objects have not net flow between them
• triple point is one specific point temperature and pressure where the three phases of matter of substances can exist in thermal equilibrium
• absolute temperature

  • uses triple point of water and absolute 0 as fixed points
  • kelvin and has same increments as celsius
  • a change in 1k is the same as 1 celsius
  • always positive
• kelvin=celsius + 273
• If one object is hotter than the other then there will be a net flow of thermal energy from the hotter to the colder object, increasing the temperature of the colder object and therefore decreasing the temperature of the hotter one until thermal equilibrium is reached
• any object at 100 degrees celsius must be in thermal equilibrium with boiling water
• Brownian motion is the random motion of particles
• internal energy is the sum of randomly distributed kinetic and potential energies of the particles in a given system
• specific heat capacity os the amount of energy required to increase the temperature of a 1kg substance by 1 degree
• specific latent heat is the amount of energy required to change the states of 1kg of a substance without a change in temperature
• during a change in state the potential energy of particles change but the kinetic energies don't change
• Boyles law is when pressure is inversely proportional to volume
• the amount of substance indicates the number of elementary entities within a given sample of a substance
• one mole is defined as many elementary entities as there are atoms in 0.012kg of carbon 12
• total mass = number of moles x molar mass
• total number of entities = number of moles x 6.02x10^23
• kinetic theory of gases

  • a gas contains a very large number of atoms or moles moving in random directions with random speeds
  • atoms or molecules of gas occupy a negligible volume of atoms with volume of gas
  • collisions with atoms and the walls are perfectly elastic
  • the times of collisions between atoms is negligible compared to the time between collisions
  • electrostatic forces between atoms are negligible except during collisions
• when atoms hit walls then elastic collisions lead to a velocity change from u to -u and total change in momentum is -2mu
• newtons second law means that the force on the atom is equal to momentum over the time
• from newtons third law we can say that the atoms must also exert an equal and opposite force on the wall
• the total force of the atoms hitting the walls randomly causes a pressure over a given area
• Boyles law states that the pressure of an ideal gas is inversely proportional to its volume provided that the mass and temperature stays constant
• a pressure-1/volume graph should show a straight line through the origin with a constant gradient
• if the volume and mass of a gas remain constant, the pressure of an ideal gas is directly proportional to it absolute temperature
• absolute zero is the lowest possible temperature where substances have minimum internal energy