Unleashing the Wonders of Force and Laws of Motion: CBSE Class 9 Science at Future Classes
The CBSE Class 9 Science syllabus includes a unit on Force and Laws of Motion. This unit explains the concepts of force, inertia, momentum and acceleration, and how they are related to each other. It also covers the three laws of motion – Newton’s laws of motion – and how they help us to understand the motion of objects. These notes provide a comprehensive overview of the concepts and their applications.
Our website is proud to offer PDF downloads of notes for Force and Laws of Motion, as part of CBSE Class 9 Science curriculum. These notes provide comprehensive and detailed coverage of topics such as Newton's Three Laws of Motion, inertia, momentum, and more. Our PDF downloads are easy to use, and can be printed or shared with others. They are a great resource for both teachers and students alike, and are sure to help improve your understanding of the Force and Laws of Motion.
Force and laws of motion
Force
It is the force that enables us to do any work. To do anything, either we pull or push the object. Therefore, pull or push is called force.
For example, to open a door, either we push or pull it. A drawer is pulled to open and pushed to close.
Effect of Force
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Force can move a stationary body.
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Force can stop a moving body.
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Force can change the direction of a moving object.
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Force can change the speed of a moving body.
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Force can change the shape and size of an object.
Forces are mainly of two types
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Balanced forces
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Unbalanced forces
Balanced Forces
If the resultant of applied forces is equal to zero, it is called balanced forces.
For example, in the tug of war, if both the team applies a similar magnitude of forces in opposite directions, the rope does not move on either side.
Unbalanced Forces
If the resultant of applied forces is greater than zero, the forces are called unbalanced forces.
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).
The inertia of an object is measured by its mass. Inertia is directly proportional to the mass. This means inertia increases with an increase in mass and decreases with a decrease in mass.
Momentum
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Momentum is the power of motion of an object.
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The product of velocity and mass is called momentum. Momentum is denoted by ‘p’.
Laws of Motion
Newton’s First Law of Motion (Law of Inertia)
Any object remains in the state of rest or uniform motion along a straight line until it is required to change the state by applying an external force.
Statement of Second Law
The rate of change of momentum of an object is proportional to the applied unbalanced force in the direction of the force.
Mathematical expression
According to second law, this rate of change of momentum is directly proportional to force.
1 Newton
When an object of mass 1 kg and its acceleration is 1 m/sec2, then the force applied on the body is said to be 1 Newton.
Third Law of Motion
To every action, there is an equal and opposite reaction.
Applications:
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Walking is enabled by third law.
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A boat moves back when we drown it.
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A gun recoils.
Law of Conservation of Momentum
When two (or more) bodies act upon one another, their total momentum remains constant (or conserved) provided no external forces are acting.
Proof
Suppose, two objects A and B each of mass m1 and mass m2 are moving initially with velocities u1 and u2, strike each other after time t and start moving with velocities v1 and v2 respectively.
