# Lesson Notes By Weeks and Term - Junior Secondary School 3

MAN IN SPACE

SUBJECT: BASIC SCIENCE

CLASS:  JSS3

DATE:

TERM: 3RD TERM

WEEK 2

TOPIC:    MAN IN SPACE

FEELING OF MAN IN SPACE

When a man stands on the floor, his weight acts down on the floor and the floor acts back on the man with a reaction equal in magnitude to his weight. The man feels the reaction from the floor and this makes him aware of how heavy he is. He could actually read his weight by standing on a bathroom-weighing machine. The machine records the value of he reaction on him. If the man carries the machine into a lift and stand on it, the machine gives the same as before for his weight.

The earth is surrounded by a layer of air called atmosphere. This atmosphere is divided into about four regions namely troposphere, stratosphere, ionosphere, and exosphere. The place beyond the atmosphere which is extremely large is called space.

EVALUATION

(1)    What is the name given to a layer of air that surrounded the earth?

(2)    What is the place beyond the atmosphere called?

SUBTOPIC: GRAVITATIONAL FORCE

Gravitational force is a force which attracts bodies towards the earth.

When you throw any object up, it is observed that the object is forced back to the ground. This also accounts for why fruits fall to the ground from the tree, and do not rise upwards again. The earth is behaving like a magnet

Gravity is the force with which the earth attracts objects towards its centre. Gravitation pull comes from this concept of gravity.

EVALUATION

1. Define gravitational force
2. What is gravity?

SUB-TOPIC:  THE GRAVITATIONAL PULL AND WEIGHT

The amount of force with which gravity pulls an object depends on three things namely:

1. The mass of the object
2. The mass of the earth
3. The distance between the centre of the object and the earth

There is difference in weight when an object is weighed on the surface of the earth and when it is weighed high above the earth’s surface. The weight of an object can change as it is moved from one place to another whereas some mass does not change unless some amount of material is taken away from it or added to it.

EVALUATION

1. Mention three factors by which the amount of force with which gravity pulls an object it depends on.

SUB-TOPIC: WEIGHTLESSNESS

Weightlessness is a feeling of being weightless. It does not mean having no weight. Weight is the force exerted by the earth on a body. A body is really never weightless of gravitational pull or another.

SPACE TRAVEL

The scientist are occupied with space travel in order to view the earth and to know how possible is life on the other planets

The force which keeps the body moving round the earth is called centrifugal force. Weightlessness makes object to float freely.

WEEKEND ASSIGNMENT

1. The moon is called the satellite of the earth because ______

(a) it rotates round the earth

(b) It rotates round the sun

(c) It is close to the earth

(d) It is in the universe

1. The quantity of matter in a body is called   (a) weight (b) mass (c) gravity    (d) height
2. The earth is surrounded by these layers except (a) Locosphere   (b) Exosphere   (c) Stratosphere (c) Ionosphere
3. The place beyond the atmosphere which is extremely large is called ____ (a) space (b) mass (c) vacant (d) vacuum

THEORY

1. What is weightlessness?
2. What is centrifugal force?