Seat belts stretch slightly,
increasing the time taken for
the wearer to stop. This
reduces the forces acting on
the chest.
Crumple zones crumple
on impact, increasing
the time taken for the
car to stop
Air bags also
slow you down
more gradually
Cycle and motorcycle
helmets provide
padding that increases
the time taken for your
head to come to a stop
if it hits something
hard
Work
When a force moves an
object it does work and
energy is transferred to
the object
Work done by a
force= Force x
Distance moved
Forces
The resultant force is
the overall force acting
on an object
An interaction pair
is two equal forces
which are in
opposite directions
When an object is moving relative
to one another, both objects
experience a force in the direction
that opposes the movement- this is
called friction. Friction is a reaction
force
Speed, Acceleration and Velocity
Speed= distance/ time
The steeper the
gradient the
faster it's going
When distance is given
with a particular
indication of direction
it's called displacement
Acceleration is the change in
velocity in a certain amount of
time. Deceleration is just
negative acceleration
Acceleration= Change in
velocity(m/s)/ time taken
Velocity describes both
the speed and direction
e.g 30 mph due north
GPE
Change in GPE= Weight x
Vertical height difference
GPE is the energy stored in
an object when you raise it
to a height against the force
of gravity
Falling objects convert GPE
into Kinetic energy
Kinetic energy
Kinetic energy= 1/2 x
mass x velocity
squared
To increase something's
kinetic energy , you need
to increase it's velocity