# Lesson Notes By Weeks and Term - Senior Secondary 1

Motion in matter

Term: 1st Term

Week: 4

Class: Senior Secondary School 1

Age: 15 years

Duration: 40 minutes of 5 periods each

Date:

Subject:      Physics

Topic:-       Motion in matter

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

1. Define Motion

1. State the causes of Motion

1. Explain circular Motion

1. Discuss centripetal Acceleration and Force

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

 PRESENTATION TEACHER’S ACTIVITY STUDENT’S ACTIVITY STEP 1 INTRODUCTION The teacher reviews the previous lesson on the measurement of mass. Weight and time Students pay attention STEP 2 EXPLANATION He defines motion and states the causes of motion Students pay attention and participates STEP 3 DEMONSTRATION He explains circular motion and discusses the centripetal acceleration and force Students pay attention and participate STEP 4 NOTE TAKING The teacher writes a summarized note on the board The students copy the note in their books

NOTE

MOTION IN NATURE

Motion is the change of position of a body with time. The study of motion without involving the force causing the motion is called kinematics. The study of motion of objects and the forces acting on them is called dynamics.

Types of Motion

1. Translational motion: This type of motion occurs when a body moves in a fixed direction without rotating e.g. A car moving in one direction from one town to another, movement of a man etc. It is also called rectilinear motion

1. Rotational or Circular motion: This is the movement of a body in a circular manner about its axis e.g. the movement of car wheels, electric fan blade, earth about its axis etc.

1. Random Motion: This is a type of motion in which a body moves in a zigzag or disorderly manner with no specific direction e.g. motion to molecules of gasses, butterflies etc.

1. Vibratory or Oscillatory Motion: This is a to and fro or up and down movement of a body about a fixed point e.g. the simple pendulum, vibration of plucked guitar string, etc.

Relative Motion

If two bodies, A and B are moving on a straight line, the velocity of A relative to B is found by adding the Velocity of B revered to the velocity of A. For instance, if a car traveling on a straight road at 100km/hr passes a bus going in the same direction at 60km/hr., the velocity of the car relative to the bus is (-60+100) = 40km/hr. If the car and the bus are traveling in opposite direction with the same velocities of 100km/r and 60km/hr respectively, the velocity of the car relative to the bus is ( -(-60) + 100) = (60 +100) = 160 km/hr.

NB: When the velocities are not in the same straight line, the parallelograms law should be used to add this since velocities are vectors, and their magnitudes and direction must be taken into consideration.

CAUSES OF MOTION

All objects will continue in their state of rest unless acted upon by force. Only the application of a force can cause visible motion. Hence, force causes motion. There are two types of force (a) Contact force (b) Field force

1. Contact Force: They are forces that are in contact with the body they affect e.g. tension, reaction frictional forces, forces of pull & push, viscous force etc.
2. Field Force: They are forces whose sources do not require contact but the effect of such forces is felt in a field of the force e.g. electrical force, magnetic, gravitational pull etc.

CIRCULAR MOTION

In physics, circular motion is movement along a circular path or orbit. It can be uniform (i.e. with constant angular rate of rotation) or non-uniform (i.e. with a changing rate of rotation)

Formulae for uniform circular motion

Consider a body of mass (kg), moving in a circle of radius r (m), with an angular velocity of ω (rads-1)

1. The angular velocity is w = Ө/t where Ө-angle subtended (rad) & t-time (s)
2. The linear speed is v = s/t where s-distance covered (m)
3. The linear speed is v = r×ω (m/s)
4. The centripetal (inward) acceleration is a = r×ω2 = v2/r (m/s2)
5. The centripetal force is F = m×a = r×m×ω2 = mv2/r (N)
6. The momentum of the body is p = m×v = r×m×ω(kgm/s)
7. The moment of inertia is I = r 2×m (kgm2)
8. The angular momentum is L = r×m×v = r 2×m×ω = (kg·m2s−1).

1. The kinetic energy is E = ½(m×v2) = ½(r2×m×ω2) = ·p2 (2·m)−1 = ½(I·ω2) = ½(L2) (J).
2. The circumference of the orbit is 2πr (m).

1. The period of the motion is T = 2πω−1 (s)

1. The frequency is f = T−1 (Hz)

(To convert radian from degree 3600=2∏)

CENTRIFUGAL FORCE

Centrifugal force is a force that acts in opposite direction to the centripetal force.

Centrifugal force is an outward force associated with rotation.

EVALUATION:    1. What is kinematics?

1. Define motion
2. List two types of motion and explain briefly each of them giving in each case one example
3. Explain the causes of motion
4. Define centripetal and centrifugal force
5. A body of mass 5kg moving in a circular path with a velocity of 5m/s for 10 complete revolution within 4s. If the radius of the circular path is 30m, find:
1. the centripetal force
2. the centripetal acceleration