Week 4 – Jss 1 Third Term Basic Science & Technology (BST) Lesson Notes

 WEEK FOUR
CALCULATION OF GRAVITATIONAL FORCE

• Calculation of gravitational force
  
• Balanced and unbalanced forces
  
• Frictional force
  
• Uses/Advantages
  
• Disadvantages
  

 Calculation of gravitational force
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/s²)
Joule is the unit of work done.
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 unbalanced. The sum of such forces is not zero. Such forces are either acting in it are 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.

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 an arrow, or depending on the direction
Friction force
Frictional force is the force that act between the surfaces of solid objects and tends to oppose their motion over each other
Uses/Advantages

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

Disadvantages

1. It causes wear and tear of machine parts of machine
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

CLASSWORK 4

1. Define frictional force?
   
2. Enumerate two advantages of friction
   
3. Highlight two disadvantages of friction
   

ASSIGNMENT 4
SECTION A

1. Which of the following forces requires contact for its action (a) gravitational force     (b) frictional force     (c) magnetic forces (d) electrical force
   
2. The sum of balanced forces is (a) zero (b) greater than zero (c) less than zero (d) about one
   
3. The S.I unit of force is (a) Kilogram (b) Watt (c) Newton (d) Power
   
4. All of the following are correct except one (a) forces causes motion     (b) forces cause change in the direction of motion (c) forces stops motion (d) force is always parallel
   
5. One of the following force is non-contact force (a) electric force (b) push (c) tension (d) push
   

SECTION B

1. Calculate the force acting on a body of mass 0.6kg (g=9.8ms^-2; f=mg)
2. What is the name of the instrument used to measure the weight of a body?