Questions and Answers
What is force?
A force is a push or pull acting on a body which changes or tends to change the state of rest or of uniform motion. It's a vector quantity.
What is the SI/CGS unit of force?
Newton/dyne
What is one newton?
One newton is a force which, when acted upon a body of mass 1 kg, produces in it an acceleration of 1 m/s^2.
1 N is equal to how many dynes?
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What is a balanced force?
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What is an unbalanced force?
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What is Newton's First Law of Motion?
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What is another name for Newton's First Law of Motion?
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What is inertia?
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What is the measure of inertia of a body?
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What is inertia of rest?
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What is inertia of motion?
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What is inertia of direction?
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What is Newton's Second Law of Motion?
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What is momentum?
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What is the SI unit of momentum?
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What does the equation v^2 - u^2 = 2as represent?
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Frictional force is always?
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Give an application of Newton's Second Law.
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What are impulsive forces?
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What is impulse?
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What is Newton's III Law?
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Give an example of Newton's Third Law of Motion.
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What is the Law of Conservation of Momentum?
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What is the formula for recoil velocity?
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When is Newton's III Law applicable?
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Study Notes
Force
- Defined as a push or pull acting on a body, it can change the state of rest or uniform motion.
- Considered a vector quantity, it has both magnitude and direction.
Units of Force
- SI unit is the Newton (N), while the CGS unit is the dyne.
- One Newton is the force needed to accelerate a 1 kg mass at 1 m/s².
Force Conversions
- 1 N = 10^5 dynes.
Balanced and Unbalanced Forces
- Balanced forces do not change an object's state of rest or motion.
- Unbalanced forces result in a change in the state of an object.
Newton's First Law of Motion
- States that an object remains at rest or in uniform motion unless acted upon by an external force.
- Also known as the law of inertia.
Inertia
- Refers to an object's resistance to change in its state of rest or motion.
- Measured by mass, which quantifies the amount of inertia.
Types of Inertia
- Inertia of rest: A stationary object stays at rest; e.g., a passenger falling backward when a bus starts.
- Inertia of motion: A moving object stays in motion; e.g., a passenger leaning forward when the bus stops.
- Inertia of direction: An object's resistance to changing direction; e.g., falling to the left when a bus turns right.
Newton's Second Law of Motion
- The rate of change of momentum is directly proportional to the applied unbalanced force.
- Momentum (P) is the product of mass (m) and velocity (v); expressed as P = m*v, a vector quantity.
Momentum
- SI unit of momentum is kg·m/s.
Friction
- Frictional force is always negative, opposing the direction of motion.
Applications of Newton's Second Law
- High jump athletes land on cushioning to reduce impact.
- Karate experts use focused force to break materials.
- Seat belts are advised for car safety to restrain passengers.
Impulsive Forces and Impulse
- Impulsive forces act for a short time.
- Impulse equals force multiplied by time; SI unit is Newton-seconds (Ns).
Newton's Third Law of Motion
- States that for every action, there is an equal and opposite reaction, influencing different bodies.
Examples of Third Law of Motion
- A gun recoils upon firing a bullet.
- Swimming, walking, and rowing illustrate this law.
- Hitting a nail results in discomfort from reaction force.
Law of Conservation of Momentum
- In an isolated system, total momentum remains constant without external forces.
- Expressed as total initial momentum = total final momentum.
Recoil Velocity
- Calculated as V = -mv/M, where V is recoil velocity, M is the mass of the gun, and m is the mass of the bullet.
Applicability of Newton's Third Law
- Only valid when action and reaction forces act on different bodies.
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This quiz contains flashcards focusing on key concepts from the 'Force and Laws of Motion' chapter relevant to Class 9. Each card presents a term along with its definition, helping students to grasp the fundamental principles of force, motion, and their measurements. Ideal for quick reviews and test preparations.