Important Definitions

Question 1

speed

Answer 1

the distance travelled by an object per unit time

Question 2

velocity

Answer 2

the speed of an object in a stated direction

Question 3

acceleration

Answer 3

the rate of change of an object’s velocity

Question 4

mass

Answer 4

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

Question 5

weight

Answer 5

the downward force of gravity that acts on an object because of its mass

Question 6

gravitational field strength

Answer 6

the gravitational force exerted per unit mass placed at a point

Question 7

density

Answer 7

the ratio of mass to volume for a substance

Question 8

spring constant

Answer 8

is the constant of proportionality in Hooke’s law and is a measure of the stiffness of a spring

Question 9

solid friction

Answer 9

the resistance to motion caused when two surfaces are in contact

Question 10

moment

Answer 10

the turning effect of a force about a pivot; given by f x perpendicular d from the pivot

Question 11

centre of gravity

Answer 11

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)

Question 12

momentum

Answer 12

the quantity mass x velocity, p=mv

Question 13

impulse

Answer 13

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)

Question 14

resultant force

Answer 14

a single force which has the same effect on a body as two or more forces

Question 15

work done

Answer 15

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

Question 16

power

Answer 16

the rate at which work is done, or the rate at which energy is transferred

Question 17

efficiency

Answer 17

the fraction or percentage of energy supplied that is usefully transferred

Question 18

pressure

Answer 18

the force acting per unit area at right angles to a surface

Question 19

transverse wave

Answer 19

a wave in which the vibration is at right angles to the propagation of the wave

Question 20

longitudinal wave

Answer 20

a wave in which the vibration is forward and back, parallel to the direction of the propagation of the wave

Question 21

refractive index

Answer 21

the ratio of the speeds of light wave in two different media

Question 22

Total internal reflection

Answer 22

when a ray strikes the inner surface of a material and 100% of the light reflects back inside it

Question 23

Critical angle

Answer 23

the minimum angle of incidence at which total internal reflection occurs; incident ray that refracts along the surface of the medium at 90 degrees

Question 24

principal axis

Answer 24

the line passing through the centre of a lens perpendicular to its surface

Question 25

principal focus

Answer 25

(or focal point) the point at which rays of light parallel to the axis converge after passing through a converging lens

Question 26

monochromatic

Answer 26

describes a ray of light (or other electromagnetic radiation) of a single wavelength and single frequency

Question 27

magnetic field

Answer 27

a region of space around a magnet or electric current, in which a pole experiences a force

Question 28

direction of magnetic field

Answer 28

direction of the force on the N pole at that point

Question 29

electric field

Answer 29

a region of space in which an electric charge will experience a force

Question 30

direction of electric field

Answer 30

the direction of a force on a positive charge at that point

Question 31

current

Answer 31

the rate at which electric charge passes a point in a circuit

Question 32

e.m.f

Answer 32

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

Question 33

p.d

Answer 33

the work done by a unit charge passing through an electrical component; another name for voltage across two points

Question 34

background radiation

Answer 34

the radiation from the environment to which we are exposed all the time

Question 35

nuclear fission

Answer 35

the process by which energy is released by the splitting of a large, unstable, heavy nucleus into two or more smaller nuclei

Question 36

nuclear fusion

Answer 36

the process by which energy is released when two small light nuclei join together to form a new large, heavier nucleus

Question 37

radioactive decay

Answer 37

the emission of alpha, beta, or gamma radiation from an unstable nucleus

Question 38

half-life

Answer 38

the average time taken for half the atoms in a sample of radioactive material to decay

Question 39

redshift

Answer 39

in increase in the observed wavelength of electromagnetic radiation (including visible light) from a star or galaxy because it is moving away from us

Question 40

cosmic microwave background radiation

Answer 40

wavelength of light in the microwave region

Question 41

hubble’s constant

Answer 41

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)

Question 42

ultrasound

Answer 42

sound with a frequency higher than 20,000 Hz