ACCELERATION
All
these are examples of CHANGES in the velocity of an object. It's actually a good thing to have a
car that can change its velocity quickly, NOT so that you can reach 70 mph rapidly but so that you
could over take quickly in an emergency.
We call the rate at which something can change its velocity the
ACCELERATION of the object.
If the acceleration is positive the object is speeding up, if it
is negative it is slowing down. We call this negative acceleration a DECELERATION or a
RETARDATION.
Acceleration means an increase in velocity per second
and so the units for acceleration are (metres per second) per second
written m/s
2.
Our bodies experience a whole range of
accelerations during our lives.
A family car may reach 3 m/s
2
during acceleration, the acceleration of objects falling freely in the
Earth's gravitational field is about 10 m/s
2 and pilots of
military jets may reach up to 50 m/s
2
Acceleration
without a change of speed
This may sound impossible but
remember that acceleration is strictly a change of velocity. Now
velocity is a vector – something that has direction as well as size – in
other words it is a speed in a certain direction. So an acceleration can
be a change of size of the speed or the direction in which the object is
moving or both.
It is therefore possible for an object to
accelerate if it is moving at a steady speed but where the direction of
this speed is changing. A very good example of this is a stone on a
string being whirled round in a circle at a steady speed. The speed
does not change but the direction in which the stone is moving does – so
the stone is accelerating.
Animal acceleration
Some
animals can experience large accelerations, a perch may reach 33
m/s
2, a bush baby 180 m/s
2, a woodpecker 1000 m/s
2
when pecking and when a flea jumps it may achieve 1400 m/s
2! The
acceleration of a rifle bullet in the barrel of the rifle will be at
least 200 000 m/s
2!
