Atomic Motion The macroscopic properties of a system are based on the microscopic behavior of atoms. Macroscopic Microscopic equation of state: laws of motion: pressure, position, volume, velocity, temperature energy
Ideal Gas Energy Kinetic theory supplies the energy for an ideal gas. • Kav = (3/2)kT Convert this to the total system energy. • U = (3/2)NkT • U = (3/2)nRT Energy based on temperature and This energy is internal to the number of molecules gas.
Internal Energy The kinetic energy of an ideal gas is its internal energy. • Also called thermal energy vCM Internal energy does not include energy from external measures. • Center of mass translation • Rigid body rotation Fext • Potential from external force
Vibrations Mean particle speed is not the only source of internalRotation energy.around centerof mass Real molecules can have internal motion. • Rotation • Vibration These effects add to internal energy. Vibration at center of mass
Energy Transfer Thermal energy changes in a system. • It flows in and out • Due to changes in macroscopic properties Heat flow When it is due to temperature changes it is called heat.
Heat and Work Work is a process that Heat is a process that represents the change in the represents the change in the mechanical energy. thermal energy. • Force acting through a • Due to a difference in distance temperature • Measured in joules like • Measured in joules like energy energy
Mechanical Equivalent In the 1800’s James Joule demonstrated that mechanical work could cause a change in temperature. Heat, like work, represented a change in energy.
Calorie Heat was measured by a Since SI has a unit of energy change in temperature. (J) it remains the unit for all • 1 calorie (cal) is the amount forms of energy. of heat needed to raise 1 g • Work of water by 1 °C. • Mechanical energy • 1 kcal = 1000 cal, and is • Potential energy what we call a “Calorie” for • Dissipative energy food. • Heat • Thermal energy Calories (or kcal) are often • Internal energy used to measure heat or internal energy. 1 cal = 4.186 J
Burn It You gobble too much ice Convert to joules from kcal. cream and decide to walk up • W = (500 kcal)(1000 stairs to burn the additional cal/kcal)(4.186 J/cal) 500 Calories. • W = 2.1 x 106 J. If your mass is 60 kg, what Work climbing is W = mgh. vertical height must you • h = W / mg = (2.1 x 106 J) / climb? (60 kg)(9.8 m/s2) • h = 3600 m. Real humans are inefficient and h is closer to 700 m. next