1.1 Whenever two objects interact, the forces they
exert on each other are equal and opposite.
1.1.1 A number of forces acting at a point may
be replaced by a single force that has the
same effect on the motion as the original
forces all acting together. This single
force is called the resultant force.
1.1.1.1 A resultant force
acting on an object
may cause a
change in its state of
rest or motion.
1.1.1.1.1 If the resultant force acting
on a stationary object is
zero, the object will remain
stationary and if it is not not
zero, the object will
accelerate in the direction
of the resultant force.
1.1.1.1.1.1 If the resultant force acting on a moving object is zero, the object will continue to move at the same speed and in
the same direction and if it is not zero, the object will accelerate in the direction of the resultant force.
2 P2.1.2 Forces And Motion
2.1 The acceleration of an object is determined by
the resultant force acting on the object and the
mass of the object. a=F/m or F=m×a where F
is the resultant force in newtons, N, m is the
mass in kilograms, kg and a is the acceleration
in metres per second squared, m/s2.
2.1.1 The gradient of a
distance–time graph
represents speed.
2.1.1.1 To calculate the gradient of the line on a graph, divide
the change in the y axis by the change in the x axis.
2.1.1.1.1 The velocity of
an object is its
speed in a given
direction.
2.1.1.1.1.1 The gradient of a velocity–time graph represents
acceleration. a=v−ut where a is the acceleration in
metres per second squared, m/s2, v is the final velocity in
metres per second, m/s, u is the initial velocity in metres
per second, m/s and t is the time taken in seconds, s.
2.1.1.1.1.1.1 The distance travelled is represented by the
area under the line on the velocity-time graph.
3 P2.1.3 Forces And Braking
3.1 When a vehicle travels at a steady speed the resistive forces
balance the driving force. Most of the resistive forces are
caused by air resistance. The greater the speed of a vehicle the
greater the braking force needed to stop it in a certain distance.
3.1.1 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).
3.1.1.1 A driver's reaction time can be affected
by tiredness, drugs and alcohol.
3.1.1.1.1 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.
4 P2.1.4 Forces And Terminal Velocity
4.1 The faster an object moves through a fluid
the greater the frictional force that acts on it.
4.1.1 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 (steady speed).
4.1.1.1 W=m×g where W is the weight in newtons, N, m is the
mass in kilograms, kg and g is the gravitational field
strength in newtons per kilogram, N/kg.
5 P2.1.5 Forces And Elasticity
5.1 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.
5.1.1 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.
5.1.1.1 The extension of an elastic object is directly
proportional to the force applied, provided
that the limit of proportionality is not
exceeded: F=k×e where F is the force in
newtons, N, k is the spring constant in
newtons per metre, N/m and e is the
extension in metres, m.