Motion Class 9 Notes Science - Chapter 8
What Are Motion ?
Motion: Moving Of Body/object
Newton’s First Law of Mot ion
Body continues its state of rest or of uniform motion in a straight line unless an external force acts on it.
Inertia: Property of the body by virtue of which it opposes any change in its state of rest or of uniform motion in a straight line.
- Measure of inertia: Mass
- Greater mass have greater inertia
|Inertia of Rest: A body at rest tends to remain at rest.||Inertia of Motion: A body in uniform motion tends to remain in its motion.|
|Eg: When a bus suddenly starts moving forward, passengers in the bus fall backward.||Eg: Passengers fall forward when a fast moving train stops suddenly.|
Newton’s Second Law of Mot ion
Rate of change of momentum is directly proportional to applied force and change in momentum is along the direction of applied force.
F ∝ (ΔP/Δt) or F = (ΔP /Δt)
Newton’s Third Law of Mot ion
To every action there is an equal and opposite reaction.
- In walking, the feet push the ground and in tern ground exerts equal force in opposite direction.
It is a kind of push or pull to change the state of body/object.
Unit of Force
- Newton (SI)
- Dyne (Cgs)
Types of Force
- Balanced: Two or more forces acting on an object or a body if the net effect produced by them is zero
- Unbalanced: Two or more forces acting on an object or a body it the net effect produced by them is not zero
- Product of mass and velocity, P = mv
- SI unit: Kg m/s
Conservation of Momentum
If external forces acting on a system of bodies is zero, the net momentum remains conserved.