Definitions Flashcards
Newton’s First Law
A body will remain at rest or continue to move with constant velocity unless acted on by a force.i [e.g. June 2011 Q1]
Newton’s Second Law The rate of change of the momentum of a body is proportional to the resultant force that acts on it and in the direction
Newton’s Second Law
The rate of change of the momentum of a body is proportional to the resultant force that acts on it and in the direction
in which the resultant force acts.
Newton’s Third Law
When an object A exerts a force on an object B, object B will exert a force of equal magnitude but opposite direction on
object A. The two forces are the same type of force, (e.g. both gravitational or both electrostatic). [Various papers]
Linear momentum
The linear momentum of a body is the “product of mass and velocity” [Various papers]
(Note: that the definition is for linear momentum and not just momentum as there is another quantity angular
momentum which is not on the syllabus and so the term ‘momentum’ could be taken as referring to either angular or
linear momentum)
Impulse of a force
When (during a collision) a force 𝐹 acts on a body for a time 𝑡, the product 𝐹𝑡 is the impulse of the force. (The time 𝑡 is
the duration of the collision.) [e.g. June 2012 Q1]
Principle of conservation of
momentum
If no external force acts on a system of colliding objects, the total momentum of the objects is conserved; (i.e. the total
momentum before the collision is equal to the total momentum of the objects after the collision). [e.g. January 2011 Q1]
Elastic collision
The kinetic energy of the colliding objects before the collision is equal to the kinetic energy of the objects after the
collision. [e.g. June 2011, Q5]
Inelastic collision
The collision is inelastic if there is some loss of kinetic energy, (i.e. the kinetic energy of the colliding objects before the
collision is greater than the kinetic energy of the objects after the collision; some of the initial kinetic energy has been
transformed into other forms – usually heat).[e.g. January 2012, Q5]
Radian
An angle in radians is the ratio between the length of the arc on the circumference on subtended by the angle and the
radius of the circle
Sufficient condition for
uniform circular motion
A constant magnitude force acting in a direction perpendicular to the velocity
Centripetal
Centripetal acceleration
An acceleration that will cause the body to follow a circular path. If the body moves with a constant speed (i.e. uniform
circular motion) then the acceleration has constant magnitude (𝑎 = 𝑣2/𝑟) and is always directed towards the centre of
the circle.
Centripetal force
A force which acts on a body causing it to follow a circular path
gravitational field strength
The gravitational field strength at a point in a gravitational field is the gravitational force per unit mass experienced by a
body at that point. [e.g. June 2011, Q3]
Newton’s Law of Gravitation
The force of attraction between two given particles is inversely proportional to the square of their separation and
directly proportional to the product of their masses, (and acts along a line joining their centres of mass).
Uniform (gravitational) fields
The direction and strength of the field is constant throughout the considered region of space, (e.g. to a good
approximation the gravitational field on the surface of the Earth is uniform when distances considered are small relative
to the Earth’s radius (6400 km)).
Period (of an object in
uniform circular motion)
The time taken to travel around the circular path once
Geostationary
Geostationary orbit
An orbit with a period of 24 hours. Orbiting body is above the equator and rotates around the Earth’s centre of mass in
the same sense as the Earth does, leading to the satellite remaining in a fixed position above a given point on the Earth’s
surface [e.g. June 2010, Q2]
Displacement (shm)
The displacement is the distance (in a given direction) from the equilibrium position of the oscillating body. [e.g. January
2011, Q4]
Equilibrium position (shm)
The equilibrium position is the point where the resultant force on the oscillator is zero.
Amplitude (shm)
The magnitude of the maximum displacement achieved during a complete cycle of the oscillation, [e.g. January 2011,
Q4]
Period (shm)
The time taken to complete one full cycle of the oscillation
Frequency (shm)
The number of cycles of the oscillation completed per unit time. [January 2011, Q4]
Angular frequency, 𝜔 (shm)
𝜔 = 2𝜋𝑓 (is the rate of change of phase of the oscillator)
Simple harmonic motion
In terms of the force: The oscillatory motion produced when an object experiences a (restoring) force with a magnitude
that is proportional to the magnitude of displacement from the equilibrium position and is always directed towards the
equilibrium position
In terms of the acceleration: The motion of a body with an acceleration which has a magnitude that is proportional to
the magnitude of displacement from the equilibrium position and is always directed towards the equilibrium position
Either is acceptable [e.g. June 2011, Q2]unless you are instructed to give your answer in terms of acceleration [June
2010, Q3]
Free oscillations
Oscillations which are produced when the oscillator is disturbed and then allowed to oscillate subject only to the
restoring force of the oscillating system, for example pulling a mass on a spring down below its equilibrium position and
then releasing the mass.
Driven oscillations
Oscillations occurring in the presence of an external force (usually periodic) acting on the oscillating system – for
example pushing on a swing.
Resonance (shm)
When an oscillator is subject to a driving force that varies in time with a frequency that is the same as the frequency of
the free oscillations of the oscillator, oscillations of the oscillator will be produced with a very large amplitude. In the
absence of damping the magnitude of the oscillations would in theory increase without limit. In practice all systems have
some damping, though in a lightly damped mechanical system the large oscillations may result in catastrophic failure of
the mechanical system, (e.g. Tacoma Narrows bridge).
Pressure
When a force 𝐹 acts over an area 𝐴 the pressure 𝑝 =
𝐹
𝐴
Internal Energy
The sum of randomly distributed potential and kinetic energies of the particles (e.g. atoms or molecules) of a body or
system, [e.g. January 2012, Q4]
Thermal equilibrium
Two bodies are in thermal equilibrium if when placed in thermal contact there is not net movement of heat energy
between them. The statement that bodies are in thermal equilibrium is equivalent to the statement that they are at the
same temperature, [e.g. June 2010 Q4]
Absolute zero
The temperature at which a substance has minimum internal energy.iiii This is not the same as having zero internal energy – atoms in a solid, for example in a crystal lattice, will have potential energy at 0 K, even if at this temperature thermal motion has
ceased and therefore the contribution of kinetic energy to the internal energy is zero.
Specific heat capacity
The change in internal energy per unit mass per unit rise in temperature [Various papers]
Latent heat of fusion
The heat energy required to convert a solid at its melting point into a liquid at the same temperature, [e.g. June 2011,
Q4].
Latent heat of vaporisation
The heat energy required to convert a liquid at its boiling point into a gas at the same temperature.
Specific latent heat of fusion
The heat energy required per unit mass to convert a solid at its melting point into a liquid at the same temperature, [e.g.
June 2011, Q4].
Specific latent heat of
vaporisation
The heat energy required per unit mass to convert a liquid at its boiling point into gas at the same temperature.
Boyle’s Law
For a fixed mass of gas at constant temperature the pressure of the gas is inversely proportional to the volume it
occupies, [e.g. January 2011, Q6].
Condition for mechanical
equilibrium
“Resultant force = 0, Total moment = 0” [i.e. the resultant force
acting on the object is zero and the sum of all moments (produced
by forces acting on the object) is also zero] (June 2010, Q6)
“Net force = 0” and “Net moment = 0”, BUT “forces are balanced”
was NOT ALLOWED (Jan 2012, Q4)
Couple
“A pair of equal and opposite force (with their lines of action
separated by a distance)”, (Jan 2011, Q6)
“Two equal but opposite forces” (June 2012, Q4)
Density
Density = Mass/Volume”, or “Density is mass per unit volume”,
(allowed 𝜌 = 𝑀/𝑉 where 𝑀 and 𝑉 are suitably defined), (June
2011, Q2)
Displacement
(Not asked yet) – A vector directed from initial position to final
position having magnitude equal to the distance between those
points
Ductile
“A ductile material can be drawn into wire” or “A ductile material
has a large plastic region” (LEGACY – Jan 2009, 2821, Q6)
Elastic limit
If subject to a stress/force that produces an extension which
exceeds the elastic limit of the sample then “a (permanent)
deformation will remain when the stress/force is removed” (Jan
2010, Q7)
Extension
Length of spring/wire – Original length
Hooke’s Law
The extension (or compression) is directly proportional to the force
applied, provided the elastic limit is not exceeded” (June 2009, Q7)
“Extension is proportional to the force (applied as long as the elastic
limit is not exceeded)” (June 2011, Q7)
[Again in Jan 2012, Q6]
Line of action of a force
A straight line sharing parallel to the force considered and passing
through the point of application of the force, (i.e. the point where
the force acts on the extended body).
Moment of a force
“Moment = force x perpendicular distance from pivot/axis/point”
(Jan 2011, Q6)
“Moment = force x perpendicular distance from point / pivot” (Jan
2012 Q4)
[A fuller more useful definition would specify that the perpendicular
distance considered is the perpendicular distance from the line of
action of the force to the point under consideration]
newton
A force of 1 Newton will produce an acceleration of 1 m s−2 when
acting on a mass of 1 kg (Jan 2009, Q3)
“The (net) force (is a newton) when 1 kg mass has acceleration of
1 m s−2” (June 2010 Q3)
Plastic deformation
The material is permanently deformed – i.e. a deformation is
produced which remains after the force which produced the
deformation is removed (June 2010, Q7)
Power
“Power is the work done divided by the time taken”, or “Energy
transferred divided by the time taken” or “the rate of work done”
(June 2009, Q4)
[Again in June 2012, Q7]
Pressure
“Pressure = Force / Area” NOT “force over area” (LEGACY – January
2009, 2821 Q3)
Principle of conservation of
energy
Either “Energy cannot be created or destroyed; it can only be
transferred/transformed into other forms” or “The total energy (of
a system) remains constant” (Jan 2010, Q5)
Either “Energy can neither be created nor destroyed (but it can be
transformed from one form to another)” or “The total energy of a
closed system remains constant” (June 2011, Q6)
[Again in Jan 2012, Q2]
Principle of moments
“For equilibrium of an object, the sum of clockwise moments about
a point must be equal to the sum anticlockwise moments about the
same point” (June 2009, Q5)
Resultant force
The vector sum of all the individual forces acting on
a body
Stiff
“A stiff material has a high/large Young Modulus” (LEGACY – Jan
2009, 2821, Q6)
Stopping distance of a car
“Thinking distance + Braking distance” (Jan 2009, Q6)
Strain
“Strain = extension / original length” (LEGACY – January 2007,
2821, Q5)
Stress
“Stress = force / cross-sectional area” ” (LEGACY – January 2007,
2821, Q5)
Strong
“A strong material can take a high (maximum) stress before
breaking” (LEGACY – Jan 2009, 2821, Q6)
Torque of a couple
“torque of a couple = one of forces x perpendicular distance
(between forces)”, NOT “force x perpendicular distance”(Jan 2009,
Q4)
“torque = one of the forces x perpendicular distance between the
forces” (June 2012, Q4)
Thinking distance
“The distance travelled (by the car) from when the driver sees a
problem and the brakes are applied” (Jan 2011, Q2)
Vector quantity
“A quantity that has (both) magnitude and direction” (Jan 2009, Q1)
“A quantity with magnitude and direction” (June 2011, Q3)
[Cover both bases with “A quantity that has both magnitude and
direction”]
Velocity
“velocity = rate of change of displacement” NOT “velocity =
displacement/time” (June 2012, Q3)
Watt
“Watt is the power used when one joule of work is done per
second” (LEGACY – Jan 2007, 2821, Q3)
Work done by a force
“Work done = force x distance moved in the direction of the force”,
“Allow ‘displacement’ instead of ‘distance’” (June 2009, Q4)
“Work done = force x distance moved (in direction of force)”(June
2010, Q4)
“Work (done) = force x distance moved in the direction of the force”
(Jan 2011, Q3)
[Again in Jan 2012, Q2 and June 2012, Q3]
Absolute Uncertainty
A measurement showing how large the uncertainty actually is, and has the same units as the quantity being measured
Acceleartion of free fall, g
The acceleration f a body falling under gravity. On Earth it has a value og 9.8m/s
Acceleration, a:
the rate of change of velocity measured in meters per second squared, a vector quantity
Accuracy
The degree to which a value obtained by an experiment is close to the actual or true value
Ammeter
A device used to measure electric current , connected in series with the components
Amerer, A
S.I unit for electric current, Eg 4A
`Amplitude
The maximum displacement of a wave from its equilibrium line / mean / rest position, measured in meters (m)
Anomalous
Values in a set of data that do not fir the overall trend and so are judged not to be part of the inherent variation.
Antinode
The displacement of the particles in a stationary wave varies by the maximum amount.
Archimedes’ Principle
the upward buoyant force (upthrust) exerted on an object immersed in fluid, whether fully or partially submerged, is equal to the weight of fluid that the object displaces.
Area, A
A physical quantity representing the size part f a surface, measured in meters squared.
Average speed
A measure of the total distance traveled in a unit time.
Braking distance
the distance a vehicle travels while decelerating to a stop.
Brittle
A material that breaks with little or no plastic deformation.
Center of gravity
The point at which the entire weight of an object can be considered to act.
Center of mass
The single point at which all of the mass of the object can be assumed to be situated. For a symmetrical body of constant density, this will be at the center of an object.
Closed system
Any system in which all the energy transfers are accounted for, energy or matter cannot enter or leave.
Coherence
Two waves with a constant phase relationship.
Components of a vector
The results from resolving a single vector into horizontal and vertical parts.
Components
Parts of electric circuits, including bulbs, LDRs, thermistors, ect.
Compressive force
Two or more forces that have the effect of reducing the volume of the object on which they are acting, or reducing the length of a spring.
Conductor
A material with a high number density of conduction electrons and therefore a low resistance.
Conservation of charge
Physical law stating charge is conserved in all interactions; it cannot be created or destroyed.
Conservation of energy
Physical law stating that energy cannot be created or destroyed, just transformed into one form into another or transferred from one place to another. This is the situation in any closed system.
