Physics Definition Flashcards
Newton’s first law
A body will continue in a state of rest or uniform motion unless acted on by an external force.
Newton’s second law
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.
Newton’s third law
If body A exerts a force on body B, then body B will exert and equal and opposite force to body A.
Impulse
The change of momentum by the average resultant force applied during a time interval.
Elastic/Inelastic collision
An elastic collision conserves all KE, an inelastic one doesn’t.
Temperature
The absolute temperature is a measure of the average random kinetic energy of particles.
Absolute zero
The temperature at which all random motion of molecules stops, 0K.
Specific heat capacity
The amount of energy needed to increase the temperature of 1kg of a substance by 1K
Thermal capacity
The amount of energy needed to increase the temperature of a body by 1 K
Specific latent heat
The energy needed to change the phase of 1kg of a substance without change in temperature.
Ideal gas
A gas that has no intermolecular forces or potential energy. Undergoes elastic collisions. Has negligible volume compared to its container.
Boyle’s law
The pressure of a fixed mass of gas at constant temperature is inversely proportional to its volume.
Charle’s law
The volume of a fixed mass of gas at constant pressure is directly proportional to its temperature in Kelvin.
Pressure law
The pressure of a fixed mass of gas at constant volume is directly proportional to its temperature in Kelvin.
Newton’s law of gravitation
Every point mass attracts every other point mass with a force that is inversely proportional to the square of their separation.
Gravitational field
A region where a mass will experience an attractive force.
Gravitational field strength
The force per unit mass on a small point mass placed in the field.
Gravitational potential energy
Energy possessed by a mass in a field.
The work done taking a mass from infinity (zero PE) to its position in a field.
Gravitational potential
The work done per unit mass taking a point mass from infinity (zero PE) to its position in a field.
Simple harmonic motion
Motion where the acceleration is proportional to the displacement and directed in the opposite direction.
Phase difference
The angular difference between two identical points on two waves.
Path difference
The distance between two identical points on two waves.
Superposition
The addition of two or more waves.
Standing waves
The result when two traveling waves of the same wavelength from opposite directions superpose, creating nodes and antinodes.
Diffraction
The spreading when a travelling wave passes through or around a barrier.
Coulomb’s law
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.
Potential difference
The work done per unit charge taking a small positive charge from A to B.
Ohm’s law
The current through an ohmic conductor is directly proportional to the p.d. across it at constant temperature.
EMF
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.
One Ampere
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.
Half life
The time taken for half the nuclei to decay (or activity to halve).
Decay constant
The probability of decay in one second. Gives the rate of decay for a given number of nuclei.
Baryon
Made of 3 quarks – proton, neutron.
Meson
Made of 2 quarks – pi meson
Leptons
Electron, muon, tau, and their neutrinos.
Exchange bosons
Responsible for the interactions between particles.
Moderator
Material (e.g. graphite) used to slow down neutrons so they are absorbed by fissile 235U.
Control rods
Used to absorb neutrons to slow down the reaction – e.g. boron.
Black body
A body that re-emits all energy it absorbs.
Emissivity
The ratio of energy radiated by a body to the energy radiated by a perfect black body at same temperature.
The greenhouse effect
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.
Enhanced greenhouse effect
Burning fossil fuels increases CO2 concentration leading to temperature increase.
