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2
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The same change in momentum happens over a longer time so there is
decreased deceleration so the force decreases
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2: Newton’s laws

Inertia
•
•

a resistance to a change in motion
directly proportional to mass and resultant force needed to change the motion

Newton’s first law of motion
•

An object will remain at rest or in uniform motion unless acted upon by an external resultant
force
...


Newton’s second law of motion
•

resultant force = mass × acceleration

Weight (in N)
•
•

Mass (in kg)

the force of gravity acting on an object
weight = mass × gravitational field strength

•

the amount of matter in an object

Gravitational field strength (in N/kg)
•

10 N/kg on Earth

Terminal (constant) speed
•
•

no resultant force
e
...
When a skydiver jumps, they fall faster, and air resistance or drag forces increase
...
When the drag forces become the same
as the weight or the thrust, then the forces become balanced
...


Newton’s third law of motion
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If Body A exerts a force on Body B then Body B exerts an equal and opposite force on Body A
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3: Work and energy

Energy
•
•

When a force acts on a moving body, energy is transferred although the total
amount of energy remains constant
...


Work
•
•
•

a measure of energy transfer
work = force × distance
work = energy transfer (in the absence of thermal transfer)

Kinetic energy
•

kinetic energy =

mass × velocity 2
2

; KE =

𝑚𝑣 2
2

Change in gravitational potential energy
•

gravitational potential energy = mass × gravitational field strength × change in height
; PE = 𝑚𝑔ℎ

Springs
•

force = spring constant × extension; 𝐹 = 𝑘𝑥

Force extension (𝐹-𝑥) graphs
•

area under graph = work done in stretching; 𝑊 =

4

𝐹𝑥
2

(in a linear relationship)

2
...

limited to situations involving a pivot and parallel forces (such as a balanced metre
rule)

Moments
•
•
•

the turning effects of a force around a fixed point (a pivot)
moment of force (in Nm) = force (in N) × perpendicular distance (in m);
𝑀 =𝐹×𝑑
e
...
a spanner being used to undo a nut

5

2
...

1 AU = 1
...
47 × 1015 m
speed of light = 3 × 107 m/s

The stability of stars
•

depends upon a balance between gravitational force and a combination of gas and
radiation pressure

Fusion
•

1
...

3
...


Stars generate their energy by the fusion of increasingly heavier elements
...

In main sequence, the forces acting on a star are balanced (gravitational inward
forces match outward gas and radiation pressure forces)
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The star will begin to swell as the combination of gas and radiation pressure exceeds
the gravitational force and the forces become unbalanced
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The origin of the solar system
•
•
•

from the collapse of a cloud of gas and dust
Gravitational forces cause the matter to get closer together creating the Sun and the
planets
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7

The Hertzsprug-Russell (H-R) diagram

•

A means of displaying the properties of stars, depicting the evolutionary path of a
star
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6: The Universe

Atomic absorption spectra
•
•
•

used to identify gases from a given absorption spectrum and additional data
Absorption lines arise from gas atoms in a star’s atmosphere absorbing wavelengths
of visible light that are specific to the elements present in a star
used by scientists in the nineteenth century to reveal the chemical composition of
stars

Cosmological red shift
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•
•
•
•

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revealed initially by Edwin Hubble’s measurements on the spectra of distant galaxies
revealed that the wavelengths of the absorption lines are increased and that this
effect increases with distance
attributed to the increasing space between the distant source and observers on
Earth (as opposed to Doppler red shift)
The recession velocity increases with the distance of the galaxy and it is this that
implies that all galaxies originated from a single point

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