PHYSICS

Sunday, 8 February 2015

FORM 4: 2.8 UNDERSTANDING GRAVITY

THE MEANING OF FREE FALL

An object is falling freely when it is falling under the force of gravity only (free from the influence of other forces).

Two objects of different masses that are released simultaneously falling freely with the same acceleration.

THE MEANING OF ACCELERATION DUE TO GRAVITY

Acceleration due to gravity is the acceleration of object falling freely.

Acceleration due to gravity, g = 9.8 m s^-2

THE MEANING OF GRAVITATIONAL FIELD

Gravitational field is a region around the earth in which an object experiences a force towards the centre of the earth.

THE MEANING OF GRAVITATIONAL FIELD STRENGTH

The gravitational field strength at a point is defined as the gravitational force acting on a 1 kg mass placed at that point.

THE MEANING OF WEIGHT

The weight of an object is defined as the gravitational force acting on the object.

W = mg

W = weight

m = mass

g = acceleration due to gravity = 9.8 m s^-2 / 10.0 m s^-2

Saturday, 7 February 2015

FORM 4: 2.7 BEING AWARE OF THE NEED FOR SAFETY FEATURES IN VEHICLES

SAFETY FEATURES	FUNCTIONS
Crumple zones (front & back)	§ Design to compress during an accident to absorb energy from the impact § Lengthen the time of impact § Reduce the impulsive force
Windscreen	§ Protect the passengers of the vehicle from wind, temperature extremes and flying debris
Air bag	§ Prevent the driver from hitting the steering wheel, dashboard or windscreen
Seat belt	§ Prevent the driver from being thrown forward and hitting the windscreen or any other part of the car § To reduce the effect of inertia
Side bars in doors	§ To reduce injury to the passengers when the car is hit from the side
Anti-lock Brake System (ABS)	§ Enable drive to quickly stop the car without causing the brakes to lock
Headrest	§ Prevent the injuries of the head of the driver which will move back due to inertia when the car suddenly accelerates forward

Friday, 6 February 2015

FORM 4: 2.6 ANALYSING IMPULSE AND IMPULSIVE FORCE

THE MEANING OF IMPULSE

Impulse is defined as the product of impulsive force and time interval.

Impulse = Ft

F = impulsive force

t = time interval

Impulse is also equal to the change of momentum.

Impulse = mv – mu

mv = final momentum

mu = initial momentum

THE MEANING OF IMPULSIVE FORCE

The large force that acts over a short period of time during collisions and explosions is known as impulsive force.

Impulsive force can be defined as the rate of change of momentum in a collision or explosion.

SITUATION WHERE IMPULSIVE FORCE SHOULD BE REDUCED

A longer time of impact will result in a smaller impulsive force.

SITUATION WHERE IMPULSIVE FORCE IS BENEFICIAL

A shorter time of impact will produce a larger impulsive force.

Thursday, 5 February 2015

FORM 4: 2.5 UNDERSTANDING THE EFFECTS OF A FORCE

THE MEANING OF FORCE

A force is a push or a pull.

BALANCED FORCES

When the forces acting on an object are balanced, they cancel each other out; the net force / resultant force is equal to zero.

Balanced forces do not change the state of rest or state of motion of an object.

Thus, when an object is at rest or moves with constant velocity, all the forces acting on the body are balanced.

SITUATIONS INVOLVING BALANCED FORCES

UNBALANCED FORCES

When the forces acting on an object are not balanced, there must be net force acting on it.

Unbalanced forces produce acceleration in the direction of the net force.

SITUATIONS INVOLVING BALANCED FORCES

NEWTON’S SECOND LAW OF MOTION

The acceleration produced by a net force on an object is directly proportional to the magnitude of the net force applied and is inversely proportional to the mass of the object. The direction of the acceleration is the same as that of the net force.