Physics Chapter 3: Dynamics: Explaining Motion

 PHYSICS DEFINITION:

Newton’s Second Law of Motion: Resultant force is proportional (or equal) to mass x acceleration (or resultant force is proportional to rate of change of momentum).

Inertia: Measure of how difficult it is to change the velocity of an object, or change its speed or direction. It is a measure of the mass of an object; a massive object has large inertia.

Newton’s First Law of Motion: Object will remain at rest or in a state of uniform motion unless it is acted on by a resultant force.

Newton’s Third Law of Motion: When 2 bodies interact, the forces they exert on each other are equal in size and opposite in direction.

 

PHYSICS KEYWORD LIST:

Weight: Force on an object caused by a gravitational field acting on its mass.

Friction: Name for a resistive force when 2 surfaces are in contact and tending to slide over one another.

Centre of Gravity: Point where the entire weight of an object appears to act.

Uniform motion: Natural state of motion of an object-uniform velocity, constant speed and direction.

Resultant Force: Single force that has the same effect as all of the forces acting on an object.

Terminal Velocity: Maximum velocity reached by an object falling under gravity or accelerated by a constant force.

Resistive Force: Backwards force in the opposite direction to movement caused by friction or some other viscous force.

Drag: Force that resists the movement of a body through a fluid.

Contact Force: Force at right, angles to a surface when 2 objects are in contact.

Upthrust: Force upwards in a liquid or gas caused by the pressure in the gas or liquid.

Homogenous: Equations with the same base units on each side are homogenous.

Base Units: Defined units of the SI system from which all units are derived.

Derived Units: Units that are combinations of the base units of the SI system.

Newton: 1 N is the force that will give a 1 kg mass an acceleration of 1 m/s^2 in the direction of force.

PHYSICS CHAPTER WISE SUMMARY:

An object will remain at rest or in a uniform motion unless it is acted on by an external force. This is Newton’s First Law of Motion.

For a body of constant mass, the acceleration is directly proportional to the resultant force applied to it. Resultant force = mass x acceleration. This is a form of Newton’s Second Law of Motion.

When 2 bodies interact, the forces they exert on each other are equal in magnitude and opposite in direction. This is Newton’s Third Law of Motion.

The acceleration produced by a force is in the same direction as the force. We must determine the resultant force where there are 2 or more forces.

A newton (N) is the force required to give a mass of 1 kg an acceleration of 1 m/s^2 in the direction of force.

The greater the mass of an object, the more it resists changes in its motion. Mass is a measure of the object’s inertia.

The weight of an object is a result of the pull of gravity on it: Weight = mass x acceleration of free fall.

Terminal velocity is reached when the fluid resistance is equal to the object's weight.

Physics equations are homogenous and have the same base units on each side. The main base units are m, kg, s, A and K (the thermodynamic unit for temperature).

PHYSICS IMPORTANT NOTES:

Resultant force = mass x acceleration (F = ma)

Weight = mass x acceleration of free fall (W = mg)

All physical quantities have a numerical magnitude (a numerical size) and a unit.

Quantity	Symbol	Unit
Resultant Force	F	N (newtons)
Mass	m	kg (kilograms)
Acceleration	a	m/s^2 (metres per second squared)

 

Quantity	Symbol	Unit	In terms of base units	Comment
Mass	m	kg	kg	Doesn’t vary place to place.
Weight	mg	N	kg m/s^2	Force depends on strength of gravity.

 

Base units	Symbol	SI Unit
Length	x, l, d, s and so on	m (metre)
Mass	m	kg (kilogram)
Time	t	s (second)
Electric Current	I	A (ampere)
Thermodynamic Temperature	T	K (kelvin)
Amount of Substance	n	mol (mole)
Luminous Intensity	l	cd (candela)

 

Multiples
Multiple	Prefix	Symbol
10^12	Tera	T
10^9	Giga	G
10^6	Mega	M
10^3	Kilo	k

 

Sub-multiples
Multiple	Prefix	Symbol
10^-1	Deci	d
10^-2	Centi	c
10^-3	Mili	m
10^-6	Micro	μ
10^-9	Nano	n
10^-12	Pico	p