Forces and motion
Become
an expert
234-235
What
is energy?
244-245
Machines
Accelerating is fun, but in science
it can be confusing. This is because
acceleration doesn’t just mean speeding
up. It is any change in velocity. So, it
is also used to describe slowing down
and changing direction.
I
f
y
o
u
d
r
i
v
e
8
0
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m
(
5
0
m
i
l
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s
)
i
n
t
w
o
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o
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,
The maxium velocity of falling through air is 200 kph (124 mph).
y
o
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r
s
p
e
e
d
i
s
4
0
k
p
h
(
2
5
m
p
h
)
.
Inertia
When things are standing still or moving, they
are quite happy to continue with what they are
doing. This stubbornness is called inertia – it is
the object’s resistance to change.
The golf ball will
carry on rolling until
friction, gravity,
and air resistance
slow it down.
Balanced forces
Forces act on objects all
the time. Opposing forces
can be balanced out. When
this happens the object won’t
be pushed in any direction.
LIFT
THRUST
Speed and velocity
Speed is different to velocity. How quick you are going is
easy to work out – divide how far you travel by the time
it takes. Your velocity is how fast you travel in a particular
direction. Changing direction without slowing reduces your
velocity, but your speed stays the same.
DRAG/
FRICTION
GRAVITY
Rescue helicopters
balance forces so
they can hover
above the waves.
243
