# Lesson Notes By Weeks and Term - Junior Secondary School 1

CALCULATION OF GRAVITATIONAL FORCES

SUBJECT:� BASIC SCIENCE �� ��� ���

CLASS:� JSS1

DATE:

TERM: 3RD TERM

REFERENCE

• Precious seed BASIC SCIENCE FOR JUNIOR SECONDARY SCHOOLS BOOK 1

WEEK FOUR

CALCULATION OF GRAVITATIONAL FORCES�

CALCULATION OF WORK DONE AGAINST GRAVITY�

Suppose you lift an object of mass 1kg from the ground to a height of 1m, the work done in lifting the abject is calculated by using the formula Mgh

Mgh = 1 x 1 x 9.8 joules (g = 9.8m 152) joule is the unit of work.

BALANCED AND UNBALANCED FORCES�

When an object is stationary, the forces acting on it are balanced forces. The sum of such forces acting on the body is zero and they act in opposite direction.

When an object is in motion (moving), the forces acting on it are on balanced. The sum of such forces is not zero. Such forces are either acting in different direction or the same direction but are not equal in value. Unbalance forces cause a body to accelerate.

GENERAL EFFECT OF A FORCE�

1. A force causes motion of an object.�
2. A force causes moving object to come to rest (stop)
3. A force changes the speed of a body in motion.
4. A force causes changes in the direction of motion.

UNIT OF FORCE�

The S.I unit of force is the Newton, N. The force acting on an accelerating body of mass, m, is given by, F = ma

Force acts in a specific direction. The direction of the action of a force is usually indicated by a arrow, or� depending on the direction.�

EVALUATION�

1. Explain balanced and unbalanced forces.
2. State the S.I unit of force.

FRICTIONAL FORCE�

Frictional force is the force that act between the surfaces of solid objects and tends to oppose their motion over each other.

1. It helps in walking.�
2. It helps in carrying objects.
3. It helps in grinding.������������
4. It makes nails stay on the wall.�
5. Car brakes work by friction.�

1. It causes wear and tear of machine parts.�
2. It causes loss of energy.�
3. It produces unpleasant noise.�
4. It makes machine hot and inefficient.�

METHODS OF REDUCING FRICTION�

1. By lubricating surfaces with oil or grease.
2. Use of the ball bearing.�

EVALUATION�

1. Explain balanced and unbalanced forces.
2. State the S.I unit of force.

• Precious seed BASIC SCIENCE FOR JUNIOR SECONDARY SCHOOLS BOOK 1 page 157-159

• Nigerian Basic Science Project pg 125-129

GENERAL EVALUATION�

1. Explain balanced and unbalanced forces.
2. State the S.I unit of force.
3. Define force b. State the two types of force.�

WEEKEND ASSIGNMENT�

1. One of the following force is non-contact force A. electric force B. push C. tension�
2. none.
3. Which of the following forces requires contact for its action A. � gravitational force � B.� frictional force� C.� magnetic forces� D. all.
4. The sum of unbalanced forces is A. zero B. greater than zero C. less than zero D. 1.
5. All of the following are correct except one A. forces causes motion B. forces cause change in the direction of motion C. forces cause weightlessness D. none of the above.
6. The S.I unit of force is A. Kg B. N/m3 C. N D. Nm.

THEORY

1��� (a) Define force (b) State the two types of force.�