Definitions Flashcards
Physical quantity
Property of a material or system that can be quantified by measurement
Example: Length, mass, time
Scalar quantity
Physical quantity that has magnitude only
Example: Mass, temperature
Vector quantity
Physical quantity that has both magnitude and direction
Example: Displacement, velocity, force
Random error
Measured values are scattered about the true value with no fixed pattern
Example: Fluctuations in a thermometer reading
Systematic error
Measured values are consistently larger or smaller than the true value
Example: Zero error in a measuring instrument
Accuracy
How close the measured reading is to the true value
Example: A ruler measuring to the nearest millimeter
Precision (of a set of readings)
Determined by the range in values
Example: A set of readings with small variations
Precision (of an instrument)
Determined by the size of the smallest division
Example: A ruler with divisions of 1 mm
Uncertainty
Extent of errors
Displacement
Straight line distance from the start to the finish point in that direction
Distance
Total length of the actual path travelled between the start and finish points
Speed
Rate of change of distance
Velocity
Rate of change of displacement
Acceleration
Rate of change of velocity
Viscous drag force
Force which opposes the relative motion of a body moving through a fluid
Equations of motion
Can only use when: Motion is in a straight line with constant acceleration
Newton’s First Law
An object stays at rest or continues to move at constant velocity unless a resultant force acts on it
Newton’s Second Law
The rate of change of momentum of a body is directly proportional to the resultant force acting on it and takes place in the direction of the resultant force
Newton’s Third Law
When body A exerts a force on body B, body B exerts on body A a force of the same type: equal in magnitude and opposite in direction
Mass
The property of a body which resists change in motion
(The amount of matter/substance in a body)
Weight
The force acting on the body due to a gravitational field
Weightlessness
State where a body experiences no contact forces
Resultant force (Fnet)
Rate of change of momentum
Impulse
The product of average force and time duration of impact
Linear Momentum
Product of its mass and velocity
Principle of Conservation of Linear Momentum
The total linear momentum of an isolated system of interacting bodies before and after collision remains constant if no net external force acts on the system
Elastic collision
Total kinetic energy of system of bodies before and after collision remains the same
Inelastic collision
Total kinetic energy of system of bodies after collision is different from before
Perfectly inelastic collision
Total kinetic energy of system of bodies after collision is different from before;
Masses stick together and move off with same velocity after collision
Field of force
Region of space where a particle experiences a force due to certain properties it possesses
Friction
Force that opposes motion
Centre of gravity
The point from where all the weight of a body appears to act upon
Translational Equilibrium
No resultant force
Rotational Equilibrium
No resultant torque about any point
Hooke’s Law
The change in length of a material is directly proportional to the force applied on it, provided that the limit of proportionality is not exceeded
Principle of Moments
For a body in rotational equilibrium, sum of clockwise moments about any point is equal to sum of anticlockwise moments about the same point
Moment of a force (about a point)
Product of a force and perpendicular distance to the pivot
Couple
Pair of forces which are equal in magnitude but opposite in direction, and whose lines of action do not coincide
Torque (of a couple)
Product of one of the forces and the perpendicular distance between the forces
Work done
Product of a force and displacement in the direction of the force
Power
Work done per unit time
(Rate of work done/energy transfer)
Efficiency
Ratio of useful power output (work done) to power input (energy input)
Kinetic energy
Energy possessed by a mass due to its speed or motion
Gravitational potential energy
Energy of a mass due to its position in a gravitational field
Elastic potential energy
Ability to do work by an object when it is deformed
Principle of Conservation of Energy
The total energy of an isolated system remains constant;
Energy cannot be created or destroyed: it can only be converted from one form to another
Angular displacement
Angle swept out by a radius
Angular velocity
Rate of change of angular displacement swept out by a radius
Radian
Angle subtended at the centre of a circle by an arc length that is equal to the radius
Uniform circular motion
When an object moves around a circle with the same speed
Centripetal force
Centripetal acceleration
Gravitational field
Region of space in which a mass experiences a gravitational force
Gravitational field strength
Gravitational force of attraction per unit mass acting on a small test mass placed at that point in the field
Newton’s Law of Gravitation
Gravitational force of attraction between two point masses is directly proportional to the product of the masses and inversely proportional to the square of separation between the masses
Geostationary satellite
Satellite in orbit which is always positioned over the same geographical spot on Earth
Period: 24 hours
Travels from west to east (same as Earth)
Electric current
Rate of flow of electric charge
Electromotive force (emf)
Energy transformed from chemical to electrical per unit charge when charge is driven round a complete circuit
Potential difference (pd)
Energy transformed from electrical to other forms per unit charge when charge passes through an electrical component
Drift Velocity
Net velocity (flow) of charge (carriers in a certain direction under an externally applied electric field)
Coulomb
Quantity of electric charge that passes a given point in a circuit when a steady current of one ampere of current flows through that point for one second
Example sentence: One coulomb is equivalent to the charge of approximately 6.24 x 10^18 electrons.
Charge
Number of electrons x charge of each electron
Example sentence: The charge of an object is determined by the number of excess or deficient electrons.
Electron charge
1.6 x 10^-19C
Example sentence: The elementary charge of an electron is approximately 1.6 x 10^-19 coulombs.
Resistance
Ratio of potential difference across a component to the current passing through it
Example sentence: Ohm’s law relates resistance to voltage and current in a circuit.
Maximum power transfer
When resistance of external load is the same resistance as the internal resistance of source of e.m.f.
Example sentence: Maximum power transfer occurs when the load resistance matches the source resistance.
Direct Current Circuit
Circuit where the direction of flow of current is maintained in the same direction
Example sentence: Batteries provide direct current for many electronic devices.
Magnetic field
Region of space in which a permanent magnet, a current-carrying conductor or a moving charge may experience a magnetic force
Example sentence: The Earth’s magnetic field influences the behavior of compass needles.
Magnetic flux density
Force acting per unit current per unit length on a wire carrying a current that is normal to the magnetic field
Example sentence: Magnetic flux density is measured in teslas.
Electric field
Region of space in which an electric (stationary) charge experiences an electric force
Example sentence: Electric field lines represent the direction and strength of the electric field.
Electric field strength
Electric force per unit positive charge at a point in the field
Example sentence: Electric field strength is measured in newtons per coulomb.
Mass defect (∆m)
Difference between the total mass of individual, free nucleons and the mass of the nucleus
Example sentence: Mass defect is responsible for the binding energy in atomic nuclei.
Nuclear binding energy
The minimum energy required to separate the nucleons in a nucleus to infinity
Example sentence: Nuclear binding energy is released in nuclear reactions such as fusion and fission.
Isotope
Nuclei of the same element containing the same number of protons but different number of neutrons
Example sentence: Carbon-12 and Carbon-14 are isotopes of carbon.
Fusion
When two light nuclei combine to form a nucleus of greater mass
Example sentence: Fusion reactions power the sun and other stars.
Fission
The splitting of a heavy nucleus into two lighter nuclei of approximately the same mass
Example sentence: Nuclear power plants utilize fission reactions for energy production.
Radioactive decay
The () and () emission of ionising radiation in the form of alpha particles, beta particles or gamma ray photons from an unstable nucleus to become a more stable nucleus
Example sentence: Uranium-238 undergoes radioactive decay to form lead-206 through a series of alpha and beta decays.
Spontaneous decay
Probability of decay is unaffected by external factors such as temperature, pressure or chemical composition
Example sentence: Radioactive isotopes decay spontaneously at a constant rate.
Random decay
Not possible to predict if an unstable nucleus will decay at any point in time
Example sentence: The timing of radioactive decay events is inherently random.
Decay constant
Probability per unit time that a nucleus will decay
Example sentence: The decay constant is a characteristic property of a radioactive isotope.
Activity
Number of radioactive decays per unit time or rate of radioactive decay in the source
Example sentence: Geiger counters measure the activity of radioactive sources.
Half-life
Time taken for the number of undecayed nuclei to be reduced to half its original number
Example sentence: The half-life of carbon-14 is approximately 5730 years.
