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].
