Physics Definition

Question 1

Newton’s first law

Answer 1

A body will continue in a state of rest or uniform motion unless acted on by an external force.

Question 2

Newton’s second law

Answer 2

The rate of change of momentum is directly proportional to the unbalanced force applied to a body.

Simplified to:The acceleration of a body is proportional to the force applied and inversely proportional to the mass.

Question 3

Newton’s third law

Answer 3

If body A exerts a force on body B, then body B will exert and equal and opposite force to body A.

Question 4

Impulse

Answer 4

The change of momentum by the average resultant force applied during a time interval.

Question 5

Elastic/Inelastic collision

Answer 5

An elastic collision conserves all KE, an inelastic one doesn’t.

Question 6

Temperature

Answer 6

The absolute temperature is a measure of the average random kinetic energy of particles.

Question 7

Absolute zero

Answer 7

The temperature at which all random motion of molecules stops, 0K.

Question 8

Specific heat capacity

Answer 8

The amount of energy needed to increase the temperature of 1kg of a substance by 1K

Question 9

Thermal capacity

Answer 9

The amount of energy needed to increase the temperature of a body by 1 K

Question 10

Specific latent heat

Answer 10

The energy needed to change the phase of 1kg of a substance without change in temperature.

Question 11

Ideal gas

Answer 11

A gas that has no intermolecular forces or potential energy. Undergoes elastic collisions. Has negligible volume compared to its container.

Question 12

Boyle’s law

Answer 12

The pressure of a fixed mass of gas at constant temperature is inversely proportional to its volume.

Question 13

Charle’s law

Answer 13

The volume of a fixed mass of gas at constant pressure is directly proportional to its temperature in Kelvin.

Question 14

Pressure law

Answer 14

The pressure of a fixed mass of gas at constant volume is directly proportional to its temperature in Kelvin.

Question 15

Newton’s law of gravitation

Answer 15

Every point mass attracts every other point mass with a force that is inversely proportional to the square of their separation.

Question 16

Gravitational field

Answer 16

A region where a mass will experience an attractive force.

Question 17

Gravitational field strength

Answer 17

The force per unit mass on a small point mass placed in the field.

Question 18

Gravitational potential energy

Answer 18

Energy possessed by a mass in a field.

The work done taking a mass from infinity (zero PE) to its position in a field.

Question 19

Gravitational potential

Answer 19

The work done per unit mass taking a point mass from infinity (zero PE) to its position in a field.

Question 20

Simple harmonic motion

Answer 20

Motion where the acceleration is proportional to the displacement and directed in the opposite direction.

Question 21

Phase difference

Answer 21

The angular difference between two identical points on two waves.

Question 22

Path difference

Answer 22

The distance between two identical points on two waves.

Question 23

Superposition

Answer 23

The addition of two or more waves.

Question 24

Standing waves

Answer 24

The result when two traveling waves of the same wavelength from opposite directions superpose, creating nodes and antinodes.

Question 25

Diffraction

Answer 25

The spreading when a travelling wave passes through or around a barrier.

Question 26

Coulomb's law

Answer 26

The force experienced by two point charges is directly proportional to the product of their charge and inversely proportional to the square of their separation.

Question 27

Potential difference

Answer 27

The work done per unit charge taking a small positive charge from A to B.

Question 28

Ohm's law

Answer 28

The current through an ohmic conductor is directly proportional to the p.d. across it at constant temperature.

Question 29

EMF

Answer 29

The energy converted from chemical to electrical potential when one unit charge flows, or the workdone taking unit charge from one terminal to the other.

Question 30

One Ampere

Answer 30

Defined as the current that would cause a force of 2×10-7N per metre between two long parallel conductors, separated by 1 m in a vacuum.

Question 31

Half life

Answer 31

The time taken for half the nuclei to decay (or activity to halve).

Question 32

Decay constant

Answer 32

The probability of decay in one second. Gives the rate of decay for a given number of nuclei.

Question 33

Baryon

Answer 33

Made of 3 quarks – proton, neutron.

Question 34

Meson

Answer 34

Made of 2 quarks – pi meson

Question 35

Leptons

Answer 35

Electron, muon, tau, and their neutrinos.

Question 36

Exchange bosons

Answer 36

Responsible for the interactions between particles.

Question 37

Moderator

Answer 37

Material (e.g. graphite) used to slow down neutrons so they are absorbed by fissile 235U.

Question 38

Control rods

Answer 38

Used to absorb neutrons to slow down the reaction – e.g. boron.

Question 39

Black body

Answer 39

A body that re-emits all energy it absorbs.

Question 40

Emissivity

Answer 40

The ratio of energy radiated by a body to the energy radiated by a perfect black body at same temperature.

Question 41

The greenhouse effect

Answer 41

The Earth radiates EM radiation in the IR region of the spectrum. This is absorbed by the greenhouse gases in the atmosphere and re-radiated in all directions.

Question 42

Enhanced greenhouse effect

Answer 42

Burning fossil fuels increases CO2 concentration leading to temperature increase.