Important Definitions Flashcards
speed
the distance travelled by an object per unit time
velocity
the speed of an object in a stated direction
acceleration
the rate of change of an object’s velocity
mass
is the quantity of matter a body is composed of; mass causes the object to resist changes in its motion and causes it to have a gravitational attraction for other objects
weight
the downward force of gravity that acts on an object because of its mass
gravitational field strength
the gravitational force exerted per unit mass placed at a point
density
the ratio of mass to volume for a substance
spring constant
is the constant of proportionality in Hooke’s law and is a measure of the stiffness of a spring
solid friction
the resistance to motion caused when two surfaces are in contact
moment
the turning effect of a force about a pivot; given by f x perpendicular d from the pivot
centre of gravity
all the mass of an object could be located here (force of gravity acts on the mass) and the object would behave the same (when ignoring any spin)
momentum
the quantity mass x velocity, p=mv
impulse
the change in an objects momentum, changeinp, or the force acting on an object multiplied by time for which the force acts (F x t)
resultant force
a single force which has the same effect on a body as two or more forces
work done
the amount of energy transferred when one body exerts a force on another; energy transferred by a force when it moves; work done= energy transferred
power
the rate at which work is done, or the rate at which energy is transferred
efficiency
the fraction or percentage of energy supplied that is usefully transferred
pressure
the force acting per unit area at right angles to a surface
transverse wave
a wave in which the vibration is at right angles to the propagation of the wave
longitudinal wave
a wave in which the vibration is forward and back, parallel to the direction of the propagation of the wave
refractive index
the ratio of the speeds of light wave in two different media
Total internal reflection
when a ray strikes the inner surface of a material and 100% of the light reflects back inside it
Critical angle
the minimum angle of incidence at which total internal reflection occurs; incident ray that refracts along the surface of the medium at 90 degrees
principal axis
the line passing through the centre of a lens perpendicular to its surface
principal focus
(or focal point) the point at which rays of light parallel to the axis converge after passing through a converging lens
monochromatic
describes a ray of light (or other electromagnetic radiation) of a single wavelength and single frequency
magnetic field
a region of space around a magnet or electric current, in which a pole experiences a force
direction of magnetic field
direction of the force on the N pole at that point
electric field
a region of space in which an electric charge will experience a force
direction of electric field
the direction of a force on a positive charge at that point
current
the rate at which electric charge passes a point in a circuit
e.m.f
the electrical work done by a source (cell, battery, etc.) in moving a unit charge around a circuit; the voltage across the terminals of a source
p.d
the work done by a unit charge passing through an electrical component; another name for voltage across two points
background radiation
the radiation from the environment to which we are exposed all the time
nuclear fission
the process by which energy is released by the splitting of a large, unstable, heavy nucleus into two or more smaller nuclei
nuclear fusion
the process by which energy is released when two small light nuclei join together to form a new large, heavier nucleus
radioactive decay
the emission of alpha, beta, or gamma radiation from an unstable nucleus
half-life
the average time taken for half the atoms in a sample of radioactive material to decay
redshift
in increase in the observed wavelength of electromagnetic radiation (including visible light) from a star or galaxy because it is moving away from us
cosmic microwave background radiation
wavelength of light in the microwave region
hubble’s constant
ratio of the speed at which the galaxy is moving away from Earth to its distance from Earth (the slope of galaxy speed against distance)
ultrasound
sound with a frequency higher than 20,000 Hz
