Force and Laws of Motion Class 9 Notes

Force and Laws of Motion Class 9 Notes – A push or a pull that can influence something to move or stop moving is called force. You exert force whenever you push a door, pull a cart, throw a ball, or even just sit in a chair. Force has the power to modify the speed, direction, and shape of objects.

about force

Force and Laws of Motion Class 9 Notes

Balanced and Unbalanced Forces

Unbalanced forces and balanced forces are the two main categories of forces that might have an impact on an object.

  • Balanced forces – is the process of applying two or more forces on an object in such a way that they cancel one another out and maintain the object’s motion.
  • Unbalanced forces – occur when two or more forces are applied to an item in a way that the foce will not cancelling each other.
balanced force and unbalanced force

Net force

When multiple forces applyed on the object and resolved into one componenet known as net force. net force ultimately decide the motion of the object.

net force
Net Force

Frictional force

Friction is a force that resists or opposes the motion of an object in contact with a surface. When we apply a force to an object, the frictional force that arises between the surfaces in contact opposes the applied force and can prevent the object from moving.

frictional force
Fractional Force

First Law of Motion

The First Law of Motion, also known as the law of inertia. The fundamental principle of physics states that object at rest will stay at rest and an object in motion will keep moving in a straight line at a constant speed, unless a force acts on it.

newtons first law of motion

An object’s tendency to resist a change in its state of motion is known as inertia. This means that an object at rest will tend to remain at rest, and an object in motion will tend to keep moving in a straight line with a constant speed, unless altered by an external force, the speed remains constant.

Second Law of Motion

The second law of motion deals with how an object’s motion changes in response to an external force. It asserts that an object’s force is directly proportional to the rate at which its momentum changes (mass times velocity). Thus, an object will accelerate in the force’s direction if you apply a force to it; the more force you apply, the faster the object will accelerate. On the other hand, if there is no net force acting on an object, it will continue to move at a steady speed with the same momentum.

newtons second law

An object’s motion can be described by a physical quantity called momentum. It is described as being equal to the sum of an object’s mass and velocity. The formula for momentum (p) in mathematics is:

p = m * v

where m is the object’s mass and v is its velocity.

Third law of motion

“For every action, there is an equal and opposite reaction.”

This means that when one object exerts a force on another object, the second object will exert an equal and opposite force on the first object. In other words, forces always occur in pairs: if object A exerts a force on object B, then object B exerts an equal and opposite force on object A.

newtons third law of motion
Newton’s Third Law of Motion
Conservation of Momentum

Two balls with different masses and velocities are moving in the same direction along a straight line. They collide with each other, exerting forces on each other during the collision. After the collision, their velocities change to new values.

Conservation of momentum
Conservation of momentum

the momenta of ball A before and after the collision are mA uA and mA vA, respectively. Similarly, the momentum of ball B before and after the collision are mB uB and mB vB, respectively. The rate of change of momentum, or force, exerted during the collision is calculated for each ball, and according to the third law of motion, the forces exerted by each ball on the other are equal and opposite.

Inertial and Non-inertial frames

The first law of motion is valid in a reference frame known as an inertial reference frame. This law states that an object at rest will remain at rest and an object in motion will continue in a straight line with a constant velocity, unless acted upon by a net external force. In other words, in an inertial reference frame, the laws of physics are the same for all observers who are not accelerating.

A non-inertial reference frame is a reference frame in which Newton’s first law of motion does not hold. In a non-inertial reference frame, objects can appear to accelerate even in the absence of any net external forces. This apparent acceleration is due to the fact that the frame of reference itself is accelerating. Some common examples of non-inertial reference frames include rotating frames, accelerating frames, and frames in free fall.

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