When two object
interact, they always
exert an equal and
opposite force to
each other.
The resultant force is one single
force that replaces the effect of all
the forces acting on an object
A resultant force acting on
an object may cause a
change in its state or motion
If the resultant force
acting on the object is
zero then the object will
not move.
Forces and motion
F = ma
The gradient of a
distance-time graph
represents speed
The velocity of
an object is its
speed in a given
direction
a = v-u/t
The gradient of a
velocity- time graph
represents acceleration
Forces and braking
When a vehicle travels at a
steady speed the resistive
forces balance the driving
force.
The greater the speed of a
vehicle the great the braking
force needed to stop it in a
certain distance.
The stopping distance of a vehicle is the
sum of the distance the vehicle travels
during the driver's reaction time
(thinking distance) and the distance it
travels under the braking force (braking
distance)
A driver's reaction
time can be affected
by tiredness, drugs
and alcohol
When the brakes of a vehicle are applied,
work done by the friction force between
the brakes and the wheel reduces the
kinetic energy of the vehicle and the
temperature of the brakes increase
A vehicle's braking distance can be
affected by adverse road and weather
conditions and poor condition of the
vehicle
Forces and elasticity
A force acting on an
object may cause a
change in shape of
the object
A force applied to an elastic object such
as a spring will result in the object
stretching and storing elastic potential
energy.
For an object that is able to
recover its original shape,
elastic potential energy is
stored in the object when
work is done on the object to
change its shape.
F = k * e
Forces and Terminal Velocity
The faster an object moves through a
fluid the greater the frictional force
that acts on it
An object falling through a fluid will
initially accelerate due to the force of
gravity. Eventually the resultant force
will be zero and the object will move at
its terminal velocity.
Calculate the weight of an object using
the force exerted on it by gravitational
force: W = m * g