units 12-17 Flashcards
exaaaams
Radian
the angle subtended at the centre of a circle by an arc of length equal to the radius of the circle
Centripetal Force
resultant force acting towards the centre of the circle when object is in motion, perpendicular to motion of object
Centripetal acceleration
acceleration acts perpendicular to velocity; same magnitude, changing direction
A field
a region where a force is felt
(non-contact force felt)
Gravitational field
the force per unit mass
Gravitational force
is directly proportional to the product of the masses and inversely proportional to the square of their separation (centre to centre)
Gravitational potential at a point
defined as the work done per unit mass bringing a small test mass from infinity to the point
Gravitational potential energy at a point
defined as the work done to move a mass from infinity to that point
Geostationary satellite conditions (for orbit to be geostationary):
Orbital period = 24 hours
Orbits west to east
Remains a the same point above Earth’s surface
Best position - directly above the equator
Thermal energy
is transferred from a region of higher temperature to a region of lower temperature
Thermal equilibrium
when 2 objects are at the same temperature. There will be no net transfer of thermal energy between them when they are in contact with each other.
same temperature ≠ same thermal energy (same speed but mass may differ)
2 fixed points in thermodynamic scale:
Absolute zero = 0 K (theoretical - if truly at zero - water, vapour would collapse)
Triple point of water → temperature at which ice, water and water vapour co-exist = 273.15 K (0.01 C)
Measuring temperature (need a physical property that varies with temperature)
Density of the liquid (e.g. liquid in glass thermometers)
Volume of a fixed mass of gas at constant pressure (e.g. mercury pushed to the top of glass tube as temperature increases)
The resistance of an electrical resistor or thermistor
The e.m.f. (voltage) produced by a thermocouple (hot and cold wires used, voltmeter measures differences {almost electric field is built})
Specific heat capacity
the energy required per unit mass of a substance to raise the temperature by 1 Kelvin
Specific latent heat
the energy required per unit mass of a substance to change its state without any change in temperature
Internal energy of a system
= is the sum of the random distribution of kinetic and potential energies of its atoms or molecules
Only changes in internal energy can be measured (changes = heating or compressing gas)
{Gases have greatest internal energy}
First law of thermodynamics
states that the change in internal energy of a system, equals the net heat transfer into the system (q) plus the net work done on the system (W)
(If gas gets bigger — work done BY the system on environment
If heat transfer out of system — q is negative (as gas is smaller — smaller internal energy)
Boyle’s Law
pressure of a constant mass of gas at constant temperature is inversely proportional to its volume
Charles’s Law
directly proportional relationship between temperature and volume
{applies at low pressures and moderate-high temperatures)
Gay-Lussac’s law
for a constant mass of a gas at constant volume, pressure is directly proportional to its thermodynamic temperature
Ideal gas
a gas that obeys proportionality that ⇒ pV/T
Avogadro’s Law
equal volumes of a gas contain the same number of molecules at the same temperature and pressure
Assumptions made when considering kinetic model:
Gas is made up of a huge number of molecules moving in random directions
Volume of the gas molecules is negligible compared to volume of gas, so most of the time there are large gaps between molecules
The time a molecule spends travelling in between collisions is much larger than the duration of collision
No attractive intermolecular forces so potential energy of the molecules is zero
Gas molecule collisions are perfectly elastic so there is no loss of kinetic energy
Gas molecules behave like hard spheres and obey Newton’s laws.
Simple harmonic motion
an object vibrates in simple harmonic motion if its acceleration is directly proportional to its displacement from its equilibrium position and is in the opposite direction to the displacement
{When object is displaced — a restoring force begins to act}
