Viva - Physics Definitions

Question 1

Mass

Answer 1

Mass is a measure of an object’s inertia (i.e. its resistance to acceleration) and the kilogram is the SI unit.

Question 2

Kilogram

Answer 2

A kilogram was originally intended to be the mass of 1000 cubic cm of water. Until recently it was referenced to a cylinder of platinum-iridium alloy kept in a laboratory in France. More recently it has been defined with reference to the Planck constant, but is still very close to the mass of 1L of water.

Question 3

Mole

Answer 3

Mole is a measure of amount of substance, which is a measure of the elementary entities of a substance exist within an object or sample. One mole is equal to Avogadro’s number, 6.022*10^23 particles, which historically was defines as the same number of particles as exists in 12g of carbon-12.

Question 4

Newton

Answer 4

The Newton is the SI unit of force, and equals the force required to give a 1kg object an acceleration of 1m/s^2.

Question 5

Force

Answer 5

Force is an influence that causes the motion of an object with mass to change its velocity (i.e. to accelerate or decelerate). Force (N) = mass (kg) * acceleration (m/s^2)

Question 6

Momentum

Answer 6

Momentum is the tendency of an object to remain in motion, and is measured as mass (kg) * velocity (m/s)

Question 7

Kinetic energy

Answer 7

Kinetic energy is the energy an object possesses as a result of its motion.
KE = 1/2 * mass * velocity^2
It is the energy required to accelerate an object of a given mass from rest to its stated velocity.

Question 8

Potential energy

Answer 8

Potential energy is the energy an object has because of either its position relative to another object (gravitational potential energy), stresses within itself (elastic potential energy), its electrical charge (electrical potential energy), etc.

Question 9

Gravitational potential energy

Answer 9

GPE = height * mass * gravity

Question 10

Pressure

Answer 10

Pressure is the force exerted perpendicular to the surface of an object per unit area. The SI unit is the Pascal (Pa)
Pressure = N / m^2 = kg / M.s^2

Question 11

Pascal

Answer 11

The Pascal is the SI unit of pressure.
Pa = N / m^2 = kg / m.s^2

Question 12

mmHg

Answer 12

A non-SI unit of pressure.
1kPa = 7.5mmHg
1kPa = 10.2cmH2O

Question 13

Hydrogen Ion

Answer 13

A hydrogen ion, denoted H+, is a proton which has positive charge. The concentration of H+ ions in a solution is measured on the pH scale

Question 14

pH

Answer 14

pH is the ‘power of hydrogen’.
pH = - log(10) [H+]
Being a negative logarithmic scale, each fall in pH by 1 means the concentration of H+ ions increases by a factor of 10

Question 15

Critical temperature

Answer 15

The critical temperature is the temperature above which a particular gas can no longer be liquefied no matter how much pressure is applied to it.

Question 16

Critical pressure

Answer 16

The critical pressure is the pressure required to liquefy a gas at its critical temperature. A substance at its critical temperature and pressure is at its critical point.

Question 17

Triple point

Answer 17

The triple point of a substance is the temperature and pressure at which it can exist in equilibrium between solid, liquid and vapour phases.

Question 18

Filling ratio

Answer 18

The filling ratio is the weight of the fluid in a cylinder, divided by the weight of water required to fill the cylinder.

Question 19

Coulomb

Answer 19

The coulomb is the SI unit of electric charge. It is the amount of electricity that 1 Ampere current carries in one second. A quantity of 1 coulomb is equal to the electrical charge of 6.24*10^18 electrons or protons.

Question 20

Ampere

Answer 20

The ampere is the SI unit of electrical current. Historically it was defined as the current that would need to be passed through 2 parallel wires of infinite length, 1 metre apart, in a vacuum, to produce a magnetic force of 210^-7 N / m. It is now defined as the electrical current when 6.2410^18 elementary charges move in one second.

Question 21

Volt

Answer 21

The volt is the SI unit of electrical potential or electromotive force. It is defined as the electrical potential between two points of a conducting wire when an electric current of one ampere dissipates one watt of power between those points, or equivalently the potential difference between two points that will impart one joule of energy per coulomb of charge that passes through it.

Volt = potential energy (J) / charge (C)
= kg.m^2 / A.s^3

It can also be expressed as V = I.R (amps*ohms)

Question 22

Watt

Answer 22

The watt is the SI unit of power, which is energy per unit time (J/s)

Question 23

Ohm

Answer 23

The ohm is the SI unit of resistance. It is the resistance of a conductor through which one amp of current flows when one volt is applied to it.

Question 24

Hertz

Answer 24

Hertz is a measure of frequency in cycles per second.

Question 25

Absolute humidity

Answer 25

The mass of water vapour present in a given volume of air at a given temperature - kg.m^-3

Question 26

Relative humidity

Answer 26

The mass of water in a given volume of air, expressed as a percentage of the maximum mass of wter that the air could hold at the given temperature.

Question 27

Absolute zero

Answer 27

The lowest possible temperature, where all thermal motion of particles ceases - 0K or -273.15’C

Question 28

Boiling point

Answer 28

The temperature at which the vapour pressure of a liquid equals the surrounding ambient pressure and liquid changes into a vapour.

Question 29

Calorie

Answer 29

The amount of energy required to increase the temperature of 1g (1cm^3) of water by 1’C. 1 calorie = 4.16 J

Question 30

Freezing point

Answer 30

The temperature at which the liquid and solid phases of a substance of specified composition are in equilibrium at a given pressure. A liquid turns into a solid when its temperature is lowered below its freezing point.

Question 31

Gas

Answer 31

One of the four fundamental states of matter found between the liquid and plasma phase (four states = solid, liquid, gas, and plasma). There is vast separation between individual molecules and the gas will expand to fill any space available.

Question 32

Heat capacity

Answer 32

The amount of heat required to raise the temperature of an object by 1’C (specific heat capacity x mass of body). SI unit is J.K^-1