Laws of Reflection

Newton’s First Law (Law of Inertia)

An object moves with a velocity that is constant in magnitude and direction, unless acted on by a non-zero net force.

Newton’s Second Law

The acceleration (a) of an object is directly proportional to the net force acting on it and inversely proportional to its mass.

Newton’s Third Law

“Forces are always in Pairs” (Action – Reaction)

If a body A exerts a force on body B (an ‘action’), then body B exerts a force on body A (a ‘reaction’). These two forces have equal magnitude and opposite direction

Pulley. Assumptions:

• The pulley is frictionless

• The pulley has negligible mass

• The strings connecting pulleys are inextensible and have negligible masses

Terminal Speed. Assumptions:

• Object is falling in gravity (force down = weight)

• The object falls through a fluid (air or liquid) that resists the falling (resistance force is upward)

• The Terminal speed is reached when the forces of resistance equals the weight, and the Net Force = zero

Work-Kinetic Energy Theorem

• The total work done by the net external force on a system or object equals the change in kinetic energy (KE) of the system or object.

Momentum conservation

“In an isolated system the total momentum is constant at any time” OR “In an isolated system the change in total momentum is zero”

Condition for equilibrium

• Sum of all forces applied on a mass should be zero: Σ F = 0

• The sum of torques acting to give a clockwise rotation should equal the sum of torques acting to give an anti-clockwise rotation: Σ t = 0

Conservation of momentum

1) Linear momentum is conserved if the net external force is zero;

2) Angular momentum is conserved if the net external torque is zero.

Principal of superposition

Waves obey the principle of superposition: the resultant displacement at a point where similar waves from several different sources overlap is the (vector) sum of the individual wave displacements.

Huygens’s principle

Every point of a wave front may be considered the source of secondary wavelets that spread out in all directions with a speed equal to the speed of propagation of the waves.

Laws of Reflection

• Law 1:

• Law 2: The incident ray, reflected ray and the normal are in the same plane

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