NCERT Solutions for Class 9th Science
Chapter 9. Force and Laws of Motion
Chapter 9. Force And Law Of Motion
Q- What is force ?
A – It is a push or pull which change or has a tendency to change the position of body. It’s SI unit is kgm-2 .
Q- Write the Newton’s law of motion?
- A body continues to maintain its position of rest or motion unless an antennae force acts upon it
- The rate of change of momentum of body is directly proportional to the force applied and takes placed in the direction of force.
- For every action there is equal and opposition reaction.
Q:- What is balance force ?
A:- If the resultant of the several force acting a body is zero than force are said to be balance force.
Q - What is unbalance force?
A- If the resultant of the several force acting a body is not zero than force are said to be balance force.
Q – What is momentum?
A – it is quantity of motion possessed by a body is equal to the product of the mass and velocity of the body. Its SI unit is kgms-1 Momentum = mass x velocity (p=mv)
Q – Define Newton?
A - It is the unit of force.
Q – What is inertia?
A – The tendency of undisturbed objects to stay at rest or to keep
moving with the same velocity is called inertia.
Q – How can we reduce the effect of friction force ?
- Using a some their plane or surface.
- Using a lubricant.
Q- Why is the Newton’s first low of motion also called “Low of inertia”?
A – According to Newton first low of motion an object by itself is not able to change its state of rest or of uniform motion. This property of n is called inertia. That is why the Newton first low of motion is called low of Inertia.
Q- Define mass and inertia?
A –Inertia is the natural tendency of an object to result of motion. The mass of an object is a measure of its inertia.
Q- What are the different types of inertia?
A – Three types are inertia:-
- Inertia of rest.
- Inertia of motion.
- Inertia of direction.
Q- What is the unit of mass and inertia?
A – K. g.
Q- Which scientist proved first that object move with constant speed when no force acts on them?
A – Galileo.
Q- Why does moving marble stops after travelling some distance?
A - A moving marble stops after travelling some distance because of the friction. Force acting opposite to the direction of motion.
Q- Who introduced the concept of momentum?
A – Newton.
Q- Which low of motion gives the mass are of force?
A – Second low of motion.
Q - What happen when an unbalanced force is applied on the object ?
A - when an unbalanced force is applied on the object:-
- Change its speed .
- Change its direction of motion.
Q – Why safety belts are worn during driving ?
A- A sudden application of breaks may cause injury to us by impact or collisions with the panels in front safety belt are worn to prevent from such accidents. Safety belts exert a force on our to make the forward motion slower.
Q – When does an object move?
A - An object moves when the object is under the continues application of an unbalanced force.
Q – Define inertia of rest and give some example?
A- the tendency of a body to remain its position of rest is called inertia of rest. Example;-
- Dust is removed from a hanging carpet by beating with a stick. As the carpet is beaten it suddenly moves forward while the dust particle tend to remain at rest due to inertia and so fall off.
- When we snake a tree, the fruits or dry to inertia of rest.
Q - Example how Newton’s first law of motion is a special case of second law?
A - According to Newton’s second law ;-
Ft= mv – mu
That is when F=0, v=u for whatever time t is taken. This means that the object will continue moving with uniform velocity is throughout the time t. If u is zero then v will also be zero. That is the object will remain at rest.
Q – how many types of force in the third law of motion?
Q – What types of force dose make us possible to walk?
A – Reaction
Q- Name the weakest and strongest force from in nature?
- Weakest = gravitation force.
- Strongest = Nuclear force
Q – What is the SI unit of weight?