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Tuesday, 15 January 2013

CHAPTER 2 : FORCE AND MOTION_ definition list


Linear Motion is the motion of an object in a straight line.

Kinematics is the study of the of motion objects without considering the forces that cause the motion of the object.

Distance is the total length of the path covered by a moving object.

Displacement is distance from one point to another in a particular direction.

Speed is rate of change of distance. Unit m s-1

Velocity is the rate of change of displacement.

Average speed is total distance moved divided by total time taken.

Average velocity is total displacement divided by total time taken.

Acceleration is rate of change of velocity. Unit m s-2
                                                                                                                       a = v - u
                                                                                                  t


Equations of linear motion with  uniform acceleration are as follows :
                                                      v = u + at

                                                     s = ut  + ½ at2

                                                   v2  =  u2  + 2 as       

Dynamics is the study of the motion and of the forces that cause the motion of that body.

Inertia is the resistance of an object to change of its motion. Inertia is non-physical quantity.

Mass of an object is the quantity of matter in that object.

Newton’s First Law of motion states, if no external force is acting on an object, it will, if stationary remain stationary, if moving keep moving at a steady speed in a straight line.

Momentum of an object is defined as a product of mass and its velocity. Unit kg m s-1
 p = mv

Principle of conservation of momentum states that when two or more objects act on each other, their total momentum remains constant, provided there are no external forces acting on the system. 
(m1u1 + m2u2 = m1v1 + m2v2)

Force acting on an object can cause changes to its size, shape, and state of rest, velocity, and direction of motion of the object.
 
Newton’s second law of motion states that force acting on an object is directly proportional to the rate of change momentum of the object in the same direction. F = ma

Impulse is the product of force and time for which the force acts during collision

Impulsive force is the force that acts on an object within a very short time such as during a collision.

                   F = mv – mu
                                t


Gravitational attractive force is the pull (force) of the earth on objects and it acts towards the centre of the earth

An object is in free fall when it falls under the influence of gravitational attractive force without the influence of other forces. (A free fall is situation whereby an object falls under the influence of gravitational attractive force only).

Gravitational acceleration is the acceleration of an object which falls freely.
Weight of an object is the gravitational force acting on it. Or
W = mg (m = mass, g = gravitational acceleration)
An object is in equilibrium if the resultant of forces acting on it is zero.
Newton’s Third Law of Motion states that for every force there is an opposite an equivalent  force against it.
A resultant force is a single force that represents in magnitude and direction two or more forces acting on an object.
Resolving a force is replacing a single force by a pair of perpendicular forces provided that the resultant of the two forces is equivalent to the single force.
Work done by constant force to move an object is equivalent to the product of the magnitude of its displacement and the components of the force, which is in the direction of the displacement.
W = F x s

Energy is defined as the capacity of a system to do work.
Gravitational Potential Energy is defined as energy obtained by an object due to its position.
                                                      Ep = W = Fs
                                                           = mg x h
                                                           = mgh

Elastic Potential Energy is defined as energy obtained by object due to its state (extension or compression)
                                                         Ep = ½ F x  

Kinetic Energy is defined as energy attained by an object due to its motion.
W = Ek = ½ m v2  

Conservation of Energy states that energy cannot be created nor destroyed but changes from one form to another.

Elasticity of a material is its ability to return to its original form and size when the force acting on it is removed.

Hooke’s law states that the extension of an elastic spring is directly proportional to the force acting on it provided that the limit of elasticity is not exceeded.

Spring constant is defined as force per unit extension of a spring.
A soft spring has a smaller k value whereas a stiff spring has a larger k value.


The work done when extending or compressing an elastic material is given by

The strength of a material is the ability of the material to withstand external forces before it breaks or snaps. Rattan is a strong but not rigid material. Concrete is both strong and rigid.

Rigidity is the ability of a material to withstand external forces acting on it without changing its size or shape. Glass is a rigid but not a strong material.

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