Lesson Notes By Weeks and Term - Senior Secondary 1

Term: 2^nd Term

Week: 3

Class: Senior Secondary School 1

Age: 15 years

Duration: 40 minutes of 5 periods each

Date:       

Subject:      Physics

Topic:-       Gravitational Field

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

1. Explain the meaning of gravitational field
2. State Newton’s law of universal gravitation

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 field	Students pay attention
STEP 2 EXPLANATION	He explains the meaning of gravitational field	Students pay attention and participates
STEP 3 DEMONSTRATION	He states and explains Newton’s law of universal gravitation	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

GRAVITATIONAL FIELD

ACCELERATION DUE TO GRAVITY (g)

The force of gravity is the pull of attraction between the earth and objects on the surface of the earth. The value of acceleration due to gravity is constant in the region of the laboratory.

g = GM/r²

Where

G= Gravitational constant

M= Mass of the earth

R= Radius of the earth

g = Approximately 9.8ms^-2

  

NEWTON’S LAW OF UNIVERSAL GRAVITATION

 

Newton’s law of universal gravitation states that every particle of matter in the universe attracts every other particle with a force which is directly proportional to the product of their masses and inversely proportional to the square of radius between their centers.

Mathematically,

F = Gm₁m₂/r²

Where,

• F is the gravitational force between two objects measured in Newton (N).
• G is the universal gravitational constant with a value of 6.674 × 10^-11Nm²kg^-2.
• m₁ is the mass of one massive body measured in kg.
• m₂is the mass of another massive body measured in kg.
• r is the separation between them measured in kilometre (Km)

 

 

Solved Examples

1. What is the force of gravity acting on an object of mass 2000 kg at the Earth’s surface?

Given:

Mass of Earth (m₁) = 5.98 × 10²⁴kg

Mass of object (m₂) = 2000kg

The radius of the Earth (r)= 6.38 × 10⁶m

Acceleration due to gravity (g) = 9.8 m/s²

Universal constant (G) = 6.67 x 10^-11 N m² / kg²

 

Solution:

F = Gm₁m₂/r²

F = ( 6.67 x 10^-11) (5.98 × 10²⁴)(2 x 10³)/(6.38 × 10⁶)²

F = (7.978 x 10¹⁷)/ (4.07044  × 10¹³)

F = 1.959 x 10⁴ or F = 19.59 N

 

2. What is the force of gravity acting on an object of mass 1000 kg at 20,000 meters above the Earth’s surface?

 

Solution

Given:

Mass of Earth (m₁) = 5.98 × 10²⁴kg

Mass of object (m₂) = 1000kg

The radius of the Earth (r)= 6.38 × 10⁶m

Acceleration due to gravity (g) = 9.8 m/s²

Universal constant (G) = 6.67 x 10^-11 N m² / kg²

h = 2 x 10⁴ m

F = Gm₁m₂/(r +h)²

F = ( 6.67 x 10^-11) (5.98 × 10²⁴)(1 x 10³)/(6.38 × 10⁶ + 2 x 10⁴ )²

F = (3.988 x 10¹⁷)/(4.058 x 10¹³)

F = 9,827.50

F = 0.9827 x 10⁴

 

EVALUATION:   1. Define acceleration due to gravity and state its formula

2. State and explain Newton’s law of universal gravitation
3. What is the force exerted by Big Ben on the Empire State building? Assume that Big Ben has a mass of 10⁸ kilograms and the Empire State                                                         building 10⁹ kilograms. The distance between them is about 5000 kilometers and Big Ben is due east of the Empire State building.
4. What is the gravitational force that the sun exerts on the earth? The earth on the sun? In what direction do these act? (M_e = 5.98×10²⁴ and M_s = 1.99×10³⁰ and the earth-sun distance is 150×10⁹ meters).

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively