PHYSICS (CHIKAMU CHETSANANGUDZO NEMITEMO)

 

PHYSICS

DEFINITIONS, LAWS, PRINCIPLES 

#	Definitions	Laws	Principles
1a)	A scalar quantity is a quantity which can be described fully by giving its magnitude (only) e.g.: mass & energy. A vector quantity is a quantity with magnitude and direction e.g.: velocity and momentum.
b)	Coplanar vectors are vectors that are all in the same plane.
c)	Accuracy is the degree to which a measurement approaches the true value  Precision is the degree determined  by the size of the random error in the measurements. Uncertainty is the total range of values within which the measurements are likely to lie.
2a)	Distance is a product of average speed and time taken. Average speed of a particle is the distance moved divided by the time taken. Average velocity is defined as the displacement divided by the time taken. Displacement of a particle is its change of position (from one point to another in a specific/certain direction). Average acceleration is the change in velocity divided by time taken (or it can be defined as the rate of change in velocity)
3a)	Resultant force is the combined effect of several forces acting on a body.(this is a very important force in physics, thus, it shouldn't be forgotten).  Inertia is the property of a body to remain in a state of rest of uniform velocity. Mass is a measure of the inertia of a body to change in velocity. One newton (1N) is the force which will give a 1kg mass an acceleration of 1m/s^2 (1ms^-2) in the direction of the force.	NEWTON’S FIRST LAW OF MOTION: Every body continues in its state of rest, or with uniform velocity, unless acted on by a resultant force. NEWTON’S SECOND LAW OF MOTION: For a body of constant mass, its acceleration is directly proportional to the resultant force applied to it.  NEWTON’S THIRD LAW OF MOTION: Whenever one body exerts a force on another, the second body exerts an equal and opposite force on the first.
b)	The weight of a body is equal to the product of its mass and the acceleration of free fall. The centre of gravity of an object is the point at which the whole weight of the object may be considered to act.
c)	Momentum of a particle is defined as the product of its mass and its velocity. Force is the rate of change of momentum.		THE PRINCIPLE OF CONSERVATION OF MOMENTUM: If no external force acts on a system, the total momentum of the system remains constant or it is conserved.
4a)	Moment of a force is defined as the product of the force and the perpendicular distance of the line of action of the force from the pivot (Moment of a force is like the turning effect of a force). COUPLE: A pair of forces that tends to produce rotation only. Consists of two forces of equal magnitude, but opposite in direction whose lines of action don’t coincide. The torque of a couple is the product of one of the forces and the perpendicular distance between the forces.
b)	Rotational Equilibrium: a state when a body has no tendency to change its speed of rotation.		THE PRINCIPLE OF MOMENTS: For a body to be in rotational equilibrium, the sum of the clockwise moments about any point must equal the sum of the anticlockwise moments about that same point.
c)	Density of a substance is its mass per unit volume. Pressure is force per unit area, where the force F acts perpendicularly to the area A.(the capital letters are just symbols that represent the respective quantities that have been mentioned)		ARCHIMEDES’ PRINCIPLE: The up thrust acting on a body immersed in a fluid is equal to the weight of the fluid displaced.
5a)	Work done is a product of force and the distance moved by the force in the direction of the force (displacement).	LAW OF ENERGY CONSERVATION: Energy can neither be created nor destroyed. It can only be converted from one form to another.	PRINCIPLE OF THE CONSERVATION OF ENERGY: Energy cannot be created or destroyed. It can only be converted from one form to another.
b)	Kinetic Energy is energy due to motion. Potential Energy is the ability of an object to do work as a result of its position or shape. Gravitational Potential Energy is energy possessed by a mass due to its position in a gravitational field. Elastic Potential Energy is energy stored in objects which have had their shape changed elastically	NEWTON'S LAW OF GRAVITATION: Two point masses attract each other with a force that is proportional to the product of the masses and inversely proportional to the square of the separation (to be discussed in depth).
c)	Power is the work done (or energy) per unit time.
6a)	The elastic limit is the max force that can be applied to a wire/spring such that the wire/spring returns to its original length when the force is removed. Elastic Potential Energy (strain energy) is energy stored in a body due to change of shape Stress is force per unit area normal to the force.	HOOKE’S LAW: Provided the proportional limit is not exceeded, the extension of a body is proportional to the applied load.
7a)	The displacement of a particle on a wave is its distance in a specified direction from its rest position. The amplitude of the wave is defined as the maximum displacement of a particle in the wave. The wavelength is the shortest distance between two peaks or the shortest distance between two troughs. It is the shortest distance between points which are vibrating in phase with each other. It is the distance moved by the wavefront during one oscillation of the source of the waves. The period of the wave is the time for a particle in the wave to complete one vibration, or a cycle. Frequency, f, of the wave is the number of complete vibrations (cycles per unit time). Speed of the wave is the product of the frequency and its wavelength. Progressive waves are waves which transfer/move energy from place to place without the transfer of matter.
b)	A transverse wave is one in which the vibrations of the particles in the wave are at right angles to the direction in which the energy of the wave is travelling. A longitudinal wave is one in which the direction of the vibrations of the particles in the wave is along the direction in which the energy of the wave is travelling.
c)	Doppler effect: the frequency change due to the relative motion between a source of sound or light, and an observer.
8a)	Interference is the overlapping of waves. Interference pattern is the collection of fringes produced by the superposition of overlapping waves. Coherent sources are wave sources which maintain a constant phase relationship.		THE PRINCIPLE OF SUPERPOSITION: When two or more waves meet at a point, the resultant displacement at that point is equal to the sum of the displacements of the individual wave at that point.
b)	Diffraction is the spreading of a wave into regions where it would not be seen if it moved only in straight lines after passing through a narrow slit or past an edge. A Diffraction Grating is a plate on which there is a very large number of parallel, identical, very closely spaced slits.
9a)	Electric Field Strength is force per unit positive charge acting on a stationary point charge.
b)	Electric Current is a flow of charge carriers. Charge is a product of current and time. The coulomb is that charge passing a point in in a circuit when there is a current of one ampere for one second.
c)	Potential difference between two points in a circuit: a measure of the electrical energy transferred, or the work done by each coulomb of charge as it moves from one point to the other.
10a)	Electromotive Force (e.m.f.): the energy transferred by a source in the driving of unit charge round a complete circuit.
		KIRCHHOFF’S FIRST LAW (LINKED TO THE CONSERVATION OF CHARGE): The sum of the currents entering a junction in a circuit is always equal to the sum of the currents leaving it (leaving the junction).  KIRCHHOFF’S SECOND LAW (LINKED TO THE CONSERVATION OF ENERGY): The sum of the electromotive forces in a closed circuit is equal to the sum of the potential differences.