P2.1 Forces and Their Effects

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P2.1 Forces and Their Effects
P2.1.2 Forces and motion
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 X a: F=resultant force Newton: N, m=mass in kilograms: kg, a=acceleration in
metres per second squared: m/s2
Distance= Speed x Time
The velocity of an object is its speed in a given direction.
Acceleration: a = vu
a is the acceleration of the object in metres per second squared, m/s2
v is the final velocity in metres per second, m/s
u is the initial (starting) velocity in metres per second, m/s
t is the time taken in seconds, s
When an object is stationary, the line on the graph is horizontal. When
an object is moving at a steady speed in a straight line, the line on the
graph is straight but sloped.
The steeper the line, the greater the speed of the object the blue line is steeper than the red line
because the blue line represents an object which is moving more quickly.
The gradient of a velocitytime graph represents the acceleration
The area under a velocitytime graph represents the distance covered.
P2.1.3 Forces and Braking
a) When a vehicle travels at a steady speed the resistive forces balance the driving force.
b) The greater the speed of a vehicle the greater the braking force needed to stop it in a certain
c) 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
d) A driver's reaction time can be affected by tiredness, drugs and alcohol.
e) 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.
f) A vehicle's braking distance can be affected by adverse road and weather conditions and poor
condition of the vehicle.
P2.1.4 Forces and Terminal Velocity
The faster an object moves through a fluid the greater the frictional force that acts on it.
b) 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).
c) W=m X g W is weights in Newton: Nm is mass in kilograms: kg g is the gravitational
field strength in Newton per kilogram: N/kg
P2.1.5 Forces and Elasticity
Forces 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. Elastic
material is not required. Elastic potential energy is stored in the object when work is done on the object
to change its shape.
F = k X e F is force in Newton: Nk is the spring constant in Newton per metre, N/me is the
extension in metres, m


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