# Lakhmir Singh Solutions for Class 9th Physics Chapter 2: Force and Laws of Motion

The chapter revolves around the force, effect, types, laws of motion –its applications and illustrations, momentum, and conservation. In simple words, a push or pull applied to an object is called force, but its concept is not so simple. Force can be classified into two types:

• Balanced force
• Unbalanced force

While reading this chapter, the students will get to know about the most fundamental concept of physics, i.e. Newton's laws of motion and their applications.

• The first law states that a body continues to be in rest or motion until and unless an external force is applied to it.
• The second law states that the change rate of a body is directly proportional to the force applied. A cricket player moving his hands backwards on catching a fastball, the use of a seat belt in cars, and the high jump case are certain cases where Newton's second law of motion is applicable.
• The third law states that there is an equal and opposite reaction to every action of a body. Therefore, the action and reaction force acts on two different bodies. Recoiling of a gun, flying of jet planes, the case of a boat and a ship or hose pipe, a horse pulling a cart are certain cases where Newton's third law is applicable.

The chapter further explains the topic of "momentum". It can be explained as the product of the mass and velocity of a moving body. It is a vector quantity whose SI unit is kg.m/sec. Every moving body possesses momentum. E.g. a cricket ball, when thrown. Understanding the law of conservation of momentum is important as it can neither be created nor destroyed. When two or more bodies act upon one another, their total momentum remains constant, provided no external forces act. For example, whenever a gun fires a bullet, the momentum of the bullet and that of the gun remains the same.

Jet aeroplanes which include the expulsion of a large volume of gas, are certain examples of applications of the law of conservation of momentum to be studied in this chapter.