PHYSICS S.S ONE (MOTION)

FIRST TERM: WEEK 3
TOPIC: MOTION
Motion means movement. Motion can be defined as a continuous change in the position of an object. Each type of motion is controlled by different type of force. The study of objects in motion and the force associated with them is called dynamics. Kinematics is the science which studies the motion of objects.
Types of motion
1. Translational (displacement) motion: This is the motion of a body in a straight line as a result of the applied force. Translation is defined by the net force (sum of different forces) e.g vehicle moving on a straight road.
2. Rotational (circulatory) motion: This is the motion of a body that moves in a circle or ellipse and rotates about an axis. An axis is the centre around which something rotate. Rotation is defines by Torque. Torque is a force which causes the rotation of an object e.g spinning wheel, rotation of fan blades etc
3. Oscillatory (vibratory) motion: This is the motion of a body about a fixed point i.e. it is the motion that repeats itself in equal interval of time along  the same path e.g plucked violin or guitar string, swinging of the pendulum bob etc.
4. Random motion: This is a type of motion with no specific direction. Example is the zig-zag motion often exhibited by gas molecule.
5. Uniform motion: This is a motion at a constant speed in a straight line e.g. a rolling ball.
6. Circular motion: This is the motion of a body in a circle at constant speed. E.g. motion of the earth round the sun or moon round the earth. Other examples are:
A satellite circling around the earth.
The moon circling the earth
A stone tied to a string which is whirled in a horizontal or vertical circle.
CENTRIPETAL ACCELERATION
This is the acceleration that is directed towards the centre of the circular path. Its magnitude (a) is given by;   where v is the uniform speed and r is the radius of the circular path.
CENTRIPETAL FORCE
Is defined as the inward force required to keep on object moving with a constant speed in a circular path.
  Where m is the mass of the object moving with a uniform velocity v in a circular path or radius r.
ANGULAR VELOCITY ()
Angular velocity is define as the angle turned through by the body per unit time taken.
 =  =   thus, t.
This is similar to the relation distance = uniform velocity x time
For motion in a straight line.
The angle turned is measured in radians since 2. Therefore,
  Where  = in radians and s = r.
  =  x   (where  = v)
Hence, the linear speed equals the product of the angular speed and the radians or amplitude of motion.
ANGULAR ACCELERATION (a)
This is the time rate of change of its angular velocity (). It is expressed in radians per Second Square. (.
If the angular velocity of a body changes uniformly from  to  in time t seconds, then angular acceleration () is given by;  =  
Recallthat 
Therefore, =  where a is the linear acceleration of the body a = r
Linear acceleration (a) equals the product of angular acceleration () and the radius r (or the displacement of the particle from its central position).
Example:- a mass of 20kg is moving in a circular path of radius 2m with a uniform speed of 5m/s. find the centripetal acceleration and the corresponding centripetal acceleration force.
Solution:-
Centripetal acceleration is given by
 = 12.5m/s
Centripetal force is given by; F = mass X acceleration
F = 20 X 12.5 = 250N
7. Relative motion: this type of motion occurs when a stationary object seems to be in motion with a moving object. Thus, the stationary object is said to move relative to the moving object. The reason for which object are in constant motion, is due to phenomena called the force. 
Force is said to be experienced whenever there is a change in the motion or velocity of an object. It is denoted by F. Measured in Newton (N) or Kgms-2.
Types of force
There are two types of forces.
Contact force
Force field
Contact force: There are forces which are in contact or in touch with the body to which they are applied. Examples are force of push, pull, tension, reaction and frictional force.
Force field: There are forces whose sources do not require contact with the body to which they are applied. Examples are gravitational force, electrical force, magnetic force, centripetal force and centrifugal force.
Effects of Force
i. Force can make stationary object move.
ii. It can increase speed of moving object.
iii. It can stop a moving object.
iv. It can decrease speed of moving object.
v. It can change shape of an object (i.e. can deform an object).
vi. It can make an object turn about a fixed point (pivot). This is called turning effect of force.
vii. It can change the direction of a moving object.
EVALUATION
The teacher evaluates the lessons by asking the following questions from the students:
1. Define motion.
2. State the types of motion.
3. Differentiate between random and translational motion.
4. Define a force. Give two examples each of force field and contact force.
ASSIGNMENT
Write short note on frictional motion.

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