Definitions (Component 1)

Question 1

Quantity

Answer 1

In S.I. a quantity is represented by a number * a unit,

e.g. m = 3.0 kg

Question 2

Scalar

Answer 2

A scalar is a quantity that has magnitude only.

Question 3

Vector

Answer 3

A vector is a quantity that has magnitude and direction.

Question 4

Resolving a vector
into components in
particular directions

Answer 4

This means finding vectors (the so-called components)
in these directions, which add together vectorially to
make the original vector, and so, together, are
equivalent to this vector

Question 5

Density of a

material, ρ

Answer 5

Density = Mass/ Volume Unit: kg m^-3
or g cm^-3
in which mass and volume apply to any sample of the
material.

Question 6

Moment (or torque) of

a force

Answer 6

The moment (or torque) of a force about a point is
defined as the force * the perpendicular distance from
the point to the line of action of the force,
i.e. moment = F * d
Unit: Nm [N.B. the unit is not J]

Question 7

The principle of

moments

Answer 7

For a system to be in equilibrium, Sum of anticlockwise
moments about a point = Sum of clockwise moments about
the same point.

Question 8

Centre of gravity

Answer 8

The centre of gravity is the single point within a body at
which the entire weight of the body may be considered
to act.

Question 9

Displacement

Answer 9

The displacement of a point B from a point A is the
shortest distance from A to B, together with the
direction. Unit: m

Question 10

Mean Speed

Answer 10

Mean Speed = total distance travelled/ total time taken

Unit: ms^-1

Question 11

Instantaneous speed

Answer 11

Instantaneous speed = rate of change of distance

Unit: ms ^-1

Question 12

Mean acceleration

Answer 12

Mean acceleration + Change in velocity/ time taken

Unit: ms^-2

Question 13

Instantaneous

acceleration

Answer 13

The instantaneous acceleration of a body is its rate of

change of velocity. Unit: ms ^-2

Question 14

Terminal velocity

Answer 14

The terminal velocity is the constant, maximum velocity
of an object when the resistive forces on it are equal
and opposite to the ‘accelerating’ force (e.g. pull of
gravity).

Question 15

Force, F

Answer 15

A force on a body is a push or a pull acting on the body
from some external body.
Unit: N

Question 16

Newton’s 3rd law

Answer 16

If a body A exerts a force on a body B, then B exerts

an equal and opposite force on A.

Question 17

Σ F = m a

Answer 17

The mass of a body * its acceleration is equal to the
vector sum of the forces acting on the body. This
vector sum is called the resultant force

Question 18

Momentum

Answer 18

The momentum of an object is its mass multiplied by
its velocity. (p = mv). It is a vector.
UNIT: kg ms ^-1
or Ns

Question 19

Newton’s 2nd law

Answer 19

The rate of change of momentum of an object is
proportional to the resultant force acting on it, and
takes place in the direction of that force

Question 20

The principle of
conservation of
momentum

Answer 20

The vector sum of the momenta of bodies in a system
stays constant even if forces act between the bodies,
provided there is no external resultant force.

Question 21

Elastic collision

Answer 21

A collision in which there is no change in total kinetic

energy.

Question 22

Inelastic collision

Answer 22

A collision in which kinetic energy is lost

Question 23

Work, W

Answer 23

Work done by a force is the product of the magnitude
of the force and the distance moved in the direction of
the force.( W.D. = Fxcos θ )
Unit: J

Question 24

Principle of
conservation of
energy

Answer 24

Energy cannot be created or destroyed, only
transferred from one form to another. Energy is a
scalar

Question 25

Potential energy, Ep

Answer 25

This is energy possessed by an object by virtue of its

position. Ep = mgh Unit: J

Question 26

Kinetic energy, Ek

Answer 26

This is energy possessed by an object by virtue of its

motion. Ek = ½mv2 Unit: J

Question 27

Elastic potential

energy

Answer 27

This is the energy possessed by an object when it has
been deformed due to forces acting on it.
Eelastic = ½ Fx or ½ kx2
Unit: J

Question 28

Energy

Answer 28

The energy of a body or system is the amount of work

it can do. Unit: J

Question 29

Power, P

Answer 29

This is the work done per second, or energy
transferred per second.
Unit: W [= Js-1]

Question 30

Period, T for a point

describing a circle

Answer 30

Time taken for one complete circuit.

Question 31

Frequency, f

Answer 31

The number of circuits or cycles per second.

OR

The number of oscillations per second. UNIT: Hz

Question 32

Radian

Answer 32

A unit of measurement of angles equal to about 57.3°,
equivalent to the angle subtended at the centre of a
circle by an arc equal in length to the radius. UNIT: rad

Question 33

Angular

velocity, ω

Answer 33

For an object describing a circle at uniform speed, the
angular velocity ω is equal to the angle θ swept out by
the radius in time divided by t(ω = θ/t)

UNIT: rad s-1

Question 34

Simple harmonic

motion (shm)

Answer 34

Shm occurs when an object moves such that its
acceleration is always directed toward a fixed point
and is proportional to its distance from the fixed point.
(a = – ω^2 x)

Alternative definition:
The motion of a point whose displacement x changes
with time t according to x = A sin (ω t + ε), where A, ω
and ε are constants. [Variations of this kind are said to
be sinusoidal.]

Question 35

Period, T for an

oscillating body

Answer 35

The time taken for one complete cycle.

Question 36

Amplitude, A of an

oscillating object

Answer 36

The maximum value of the object’s displacement (from

its equilibrium position).

Question 37

Phase

Answer 37

The phase of an oscillation is the angle (ωt + ε) in the
equation x = A sin (ω t + ε). [ε is called the phase
constant.]
UNIT: rad

Question 38

Free oscillations

[Natural oscillations]

Answer 38

Free oscillations occur when an oscillatory system
(such as a mass on a spring, or a pendulum) is
displaced and released.
[The frequency of the free oscillations is called the
system’s natural frequency.]

Question 39

Damping

Answer 39

Damping is the dying away, due to resistive forces, of

the amplitude of free oscillations.

Question 40

Critical damping

Answer 40

Critical damping is the case when the resistive forces
on the system are just large enough to prevent
oscillations occurring at all when the system is
displaced and released.

Question 41

Forced oscillations

Answer 41

These occur when a sinusoidally varying ‘driving’ force
is applied to an oscillatory system, causing it to
oscillate with the frequency of the applied force.

Question 42

Resonance

Answer 42

If, in forced vibrations, the frequency of the applied
force is equal to the natural frequency of the system
(e.g. mass on spring), the amplitude of the resulting
oscillations is large. This is resonance.

Question 43

Ideal gas

Answer 43

An ideal gas strictly obeys the equation of state
pV = nRT, in which n is the number of moles, T is the
kelvin temperature and R is the molar gas constant.
R = 8.31 J mol-1 K
-1
. With the exception of very high
densities a real gas approximates well to an ideal gas.

Question 44

The mole

Answer 44

The mole is the S.I. unit of an ‘amount of substance’. It
is the amount containing as many particles (e.g.
molecules) as there are atoms in 12 g of carbon-12.

Question 45

Avogadro constant,

NA

Answer 45

This is the number of particles per mole.

NA = 6.02 X 10^23 mol^-1

Question 46

Internal energy, U, of

a system

Answer 46

This is the sum of the kinetic and potential energies of

the particles of a system.

Question 47

Heat, Q

Answer 47

This is energy flow from a region at higher temperature
to a region at lower temperature, due to the
temperature difference. In thermodynamics we deal
with heat going into or out of a system. It makes no
sense to speak of heat in a system

Question 48

Work, W

Answer 48

If the system is a gas, in a cylinder fitted with a piston,
the gas does work of amount p* change in V when it exerts a
pressure p and pushes the piston out a small way, so
the gas volume increases by change in V. Work, like heat, is
energy in transit from (or to) the system.

Question 49

First law of thermodynamics

Answer 49

The increase, U, in internal energy of a system is U = Q – W in which Q is the heat entering the system
and W is the work done by the system. Any of the
terms in the equation can be positive or negative, e.g.
if 100 J of heat is lost from a system Q = –100 J.

Question 50

Specific heat

capacity, c

Answer 50

The heat required, per kilogram, per degree celsius or
kelvin, to raise the temperature of a substance.
UNIT: J kg^-1 K^-1
or J kg^-1 °C^-1