# HBSE 9th Class Science Notes Chapter 9 Force and Laws of Motion

Haryana State Board HBSE 9th Class Science Notes Chapter 9 Force and Laws of Motion Notes.

## Haryana Board 9th Class Science Notes Chapter 9 Force and Laws of Motion

→ Force is a vector quantity.

→ Galileo was bom on 15th February, 1564 at Pisa in Italy.

→ First law of motion is also called law of inertia.

→ SI unit of momentum is kg ms-1.

→ The rate of change of momentum is proportional to the force applied on the body.

→ The acceleration produced in a body is proportional to the force applied on that.

→ Momentum is a vector quantity.

→ By second law of motion, we get a method to measure the applied force on body.

→ Force is obtained by multiplying the acceleration produced in a body and the mass of body.

→ In an isolated system, the total momentum remains conserved.

→ Frictional force always opposes the motion of body.

→ All solid bodies offer friction on the bodies moving on them.

→ All liquid and gaseous surfaces offer friction on bodies moving on or through them. –

→ When a body slides on other body, the friction between them is called sliding friction.

→ The friction in the bodies, which move on rollers is called rolling friction.

→ The friction depends upon the smoothness or roughness of two surfaces which are in contact.

→ Sliding friction is always much more than rolling friction for a given body.

→ Undesirable effects of friction can be controlled in some extent.

→ Those meteor, which reaches on the surface of earth is called meteorite.

→ Ball-bearings are used in machines to reduce friction.

→ Force: Force is that external factor, which changes or tends to change the position of body.

→ First Law of Motion: An object continues to be in a state of rest or of uniform motion along a straight line unless acted upon by an unbalanced force.

→ Inertia: The natural tendency of objects to resist a change in their state of rest or of uniform motion is called inertia.

→ Mass: The mass of an object is a measure of its inertia. Its SI unit is kilogram (kg).

→ Second Law of Motion: The rate of change of momentum of an object is proportional to the applied unbalanced force in the direction of force.

→ One Newton: One newton is that force which produces an acceleration of 1 ms-2 in a body of mass 1 kg.

→ Third Law of Motion: To every action, there is an equal and opposite reaction and they act on two different bodies.

→ Balanced Forces: When two or more forces acting on a body have zero resultant, then such forces are called balanced forces.

→ Unbalanced Forces: When the resultant of two or more forces acting on a body is not zero, such forces are called unbalanced forces.