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Every object tends to resist any change in
its speed or direction. This property is
called inertia. An object’s motion is only
changed when a force, such as a push
or pull, is applied. A heavy, fast-moving
object is described as having lots of
momentum. The more momentum
something has, the more difficult it is
to stop. A moving object also possesses
kinetic (movement) energy. The
principles of dynamics, or how forces
make things move, were explained
by scientist Isaac Newton (1642–1727)
in his three laws of motion.DYNAMICS NEWTON’S FIRST LAW
The first law states that an object will stay still or continue to
move at the same speed and in the same direction unless a
force acts upon it. When cars approach each other in a crash-
test laboratory, they move forward steadily. The dummies
inside each car are carried along at the same speed as the car.(^1) Inertia If the dummy has
no seatbelt, inertia will keep
it moving forward at the same
speed until it is stopped by a
part of the car that has been
slowed down by the impact –
such as the windscreen.
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