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

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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.

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GENERAL EFFECT OF A FORCE

A force causes motion of an object.
A force causes moving object to come to rest (stop)
A force changes the speed of a body in motion.
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

Explain balanced and unbalanced forces.
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.

ADVANTAGES OF FRICTION/USES

It helps in walking.
It helps in carrying objects.
It helps in grinding.
It makes nails stay on the wall.
Car brakes work by friction.

DISADVANTAGES OF FRICTION

It causes wear and tear of machine parts.
It causes loss of energy.
It produces unpleasant noise.
It makes machine hot and inefficient.

METHODS OF REDUCING FRICTION

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

EVALUATION

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

GENERAL EVALUATION

Explain balanced and unbalanced forces.
State the S.I unit of force.
Define force b. State the two types of force.
State three advantages and three disadvantages of friction.

WEEKEND ASSIGNMENT

One of the following force is non-contact force A. electric force B. push C. tension
none.
Which of the following forces requires contact for its action A. gravitational force B. frictional force C. magnetic forces D. all.
The sum of unbalanced forces is A. zero B. greater than zero C. less than zero D. 1.
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.
The S.I unit of force is A. Kg B. N/m³C. N D. Nm.