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2024年4月16日发(作者：python编程实例讲解)
Page 1
Section
1.1 (a)
1.1 (c)
1.1 (d)
1.1 (f)
1.1 (h)
1.1 (i)
1.1 (j)
1.1 (k)
1.1 (l)
1.2 (a)
Definition
Quantity
In S.I. a quantity is represented by a number a unit, (e.g. m
= 3.0 kg).
Scalar A scalar is a quantity that has magnitude only.
Vector A vector is a quantity that has magnitude and direction.
Force A force on a body is a push or a pull acting on the body from
some external body.
Unit: N
Newton’s Third Law If a body A exerts a force on a body B, then B exerts an
equal and opposite force on A.
F = m a 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.
This means finding vectors (the so-called components) in
Resolving a vector
these directions, which add together vectorially to make the
into components in
particular directions
original vector, and so, together, are equivalent to this
vector.
mass
Density of a material
Unit: kg m
3
density
volume
in which mass and volume apply to any sample of the
material.
Moment (or torque) of a The moment (or torque) of a force about a point is defined
force.
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]
The principle of For a system to be in equilibrium, sum of anticlockwise
moments. moments about a point = sum of clockwise moments about
the same point.
Centre of gravity. The centre of gravity is the single point within a body at
which the entire weight of the body may be considered to act
Displacement
The change in position. The displacement of a point B
Item
Mean Speed
from a point A is the shortest distance from A to B,
together with the direction. Unit: m.
total distance travelledx
Mean speed =
total time takent
-1
Unit: ms.
instantaneous speed = rate of change of distance
Unit: ms
-1
.
Mean velocity =
Instantaneous Speed
Mean Velocity
Instantaneous Velocity
Mean Acceleration
total displacement
total time taken
Unit: ms
-1
.
The velocity of a body is the rate of change of displacement.
Unit: ms
-1
Mean Acceleration =
change in velocityv
time takent
Instantaneous
Acceleration
Unit: ms
-2
.
The instantaneous acceleration of a body is its rate of change
of velocity. Unit: ms
-2
Page 2
Section Item
1.2 (e) Terminal Velocity
1.3 (a) Work
1.3 (b) Hooke’s Law
Spring constant, k
Definition
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).
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
)
Unit: J [= Nm]
Provided the elastic limit is not exeeded, the extension is directly
proportional to the load applied on the object.
The spring constant is the force per unit extension.
Unit: Nm
-1
.
1.3 (d) Energy
1.3 (e) Principle of
conservation of
energy
Potential energy
Kinetic energy
1.3( h) Power
Efficiency of a
system
1.4 (h) Electric current, I.
1.5 (a) Potential difference
(p.d.), V.
The ability to do work. Unit: J
Energy cannot be created or destroyed, only transferred from
one form to another. Energy is a scalar.
This is energy possessed by virtue of position. (e.g. Gravitational PE
= mgh). Unit: J
Energy due to motion. Unit: J
The work done per unit time taken. This is the work done per
second, or energy transferred per second.
Unit: watt (W) [= Js
-1
].
useful work (or energy) out
% Efficiency = 100
work (or energy) put in
UNITS: NONE
Unit: none
This is the rate of flow of electric charge. I = ∆Q/∆t. Unit: A
The p.d. between two points is the energy converted from electrical
potential energy to some other form per coulomb of charge flowing
from one point to the other. Unit: volt (V) [= JC
-1
].
1.5 (c) Ohm’s Law. The current flowing through a metal wire at constant temperature is
proportional to the p.d. across it.
1.5 (d) Electrical Resistance, The resistance of a conductor is the ratio of p.d. (V) across it to the
R. current (I) in it. R = V / I
Unit: ohm () [= VA
-1
].
1.5 (g)
Resistivity,
The resistance, R, of a metal wire of length L and cross-sectional
area A is given by R =
L / A, in which
the resistivity, is a
constant (at constant temperature) for the material of the wire.
Unit: m
1.5 (k) Superconducting The temperature at which a material, when cooled, loses all its
transition electrical resistance, and becomes super-conducting. Some materials
temperature (e.g. copper) never become superconducting however low the
temperature.
1.6 (a) The Law of Electric charge cannot be created or destroyed, (though positive and
Conservation of negative charges can neutralise each other). Charge cannot pile up
Charge. anywhere.
1.6 (f) e.m.f. f. of a source is the energy converted from some other form
(e.g. chemical) to electrical potential energy per coulomb of charge
flowing through the source.
Unit: V.
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