CALCULATION OF GRAVITATIONAL FORCE

v Calculation of gravitational force

v Balanced and unbalanced forces

v Frictional force

v Uses/Advantages

v 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. The sum of such forces acting on the body is zero and they act in opposite directions.

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 their are direction or the same direction but are not equal in value. Unbalanced forces cause a body to accelerate.

GENERAL EFFECT OF A FORCE

1.     A force causes motion of an object
2.     A force causes a 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

A 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

The frictional force is the force that acts 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 the machine
2.     It causes a loss of energy
3.     It produces unpleasant noise
4.     It makes the 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