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Linear motion
(d) From the fi rst equation of motion: in a particular direction, and is
v – u also measured in metres.
t =
g (d) Average speed measures the rate
at which the position changes.
where v = 50 m/s, u= -50 m/s
This is given by distance
Therefore, divided by time. It is measured
in metres per second, m/s.
t = 50 m/s – ( – 50 m/s) (e) Average velocity measures the
10 m/s 2
t = 10 s rate of change of displacement,
that is, displacement divided by
Therefore, the object will take 10 s time. It is measured in metres
in the air. per second, m/s.
Upon returning to its starting (f) Acceleration measures the rate
point, the object has the same of change of velocity, that is,
velocity it started with but in the change in velocity divided by
opposite direction. As expected, time. It is measured in metres
the total time in the air is twice per second squared, m/s .
2
the time required to reach the If acceleration and velocity
maximum height. The object are in the same direction, the
spends the same time going up as magnitude of velocity will
it does when comes back down. increase. If they are in opposite
directions, the magnitude of
Chapter summary velocity decreases.
1. There are several concepts used 2. Quantities like distance and
to describe motion summarised as speed have magnitude only, while
follows. displacement, average velocity and
(a) Position describes where acceleration have both magnitude
an object is based on and direction.
measurements from a chosen 3. An object’s motion can be represented
reference point. by lines and curves on distance-time
(b) Distance measures how much and velocity-time graphs.
the position has changed. It is the (a) On a distance-time graph the
length of the path followed by slope of a line represents the
object’s speed.
an object. It has magnitude only (b) On a velocity–time graph the
and is measured in metres. area under the curve represents
(c) Displacement measures the the object’s displacement, and
net change in position. It is the the slope of a line represents the
distance covered by an object object's acceleration.
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