phys definitions test Flashcards
newtons first law
an object at rest will remain at rest or in uniform motion in a straight line unless acted upon by an external resultant force
newtons second law
resultant force = mass x acceleration
newtons third law
if body a exerts a force on body b the body b exerts an equal and opposite force on body a
energy efficiency of vehicles
aerodynamic losses reduced by more streamlined designs
rolling resistance is reduced by having correctly inflated tyres and using materials which don’t heat up as much as they are squashed
stop start systems reduce idling losses
inertial losses are reduced by having lighter cars
safety features
in terms of work done - an airbag increases the distance over which the energy is transferred so reducing the force
in terms of momentum - the same in momentum happens over a longer time so there is a decreased deceleration so the force decreases
conservation of momentum
the momentum before a collision = the momentum after a collision provided no external forces act
principle of moments
for a body in equilibrium the sum of the clockwise moments = the anticlockwise moments about the same point
features of the solar system
mercury venus earth mars jupiter saturn uranus neptune
asteroid belt located between mars and jupiter
mercury venus earth mars are rocky
jupiter saturn uranus neptune are gaseous
AU and light years
1 Au is the mean distance from the sun to the earth
1 light year is the distance light will travel in 1 year
life cycle of a star
similar mass to the sun - protostar, main sequence, red giant, white dwarf
high mass star - protostar, main sequence star, supergiant, supernova, neutron star or black hole
stability of stars
in the main sequence the forces acting on the star are balanced.
gravitational forces inward match the outwards combination of gas and radiation pressure forces.
when the hydrogen reduces the star will begin to fuse helium and other increasingly heavier elements to maintain fusion
the star will begin to swell as the combination of gas and radiation pressure exceeds the gravitational force and the forces become unbalanced.
eventually the gravitational force exceeds the combination of gas and radiation pressure and shrinks.
return of heavy metal
heavy elements which are created in fusion in large stars are ejected during supernovae
origin of the solar system
gravitational forces cause the matter to get closer together, creating the sun and the planets.
during formation rocks tended to gather close to the sun and formed rocky planets whilst gaseous substances gathered together at distances further away and formed the gas planets
absorption spectra
absorption lines arise from gas atoms in a stars atmosphere absorbing specific wavelengths of visible light
the wavelengths absorbed are specific to the elements present in the star
cosmological redshift
wavelengths of the absorption lines are increased and this effect increases with distance.
the light from further galaxies shows the most red shift due to it having travelled for a greater amount of time through an expanding universe, therefore increasing the wavelength
