Exam (elaborations)
XI_Phy_New_Chap-04 Laws of Motion (95 A&R Items).
XI_Phy_New_Chap-04 Laws of Motion (95 A&R Items).
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Spread the Happiness. Assertion and Reason Statements Feedback: 9008271516XI_Phy_New_Chap-04 _ LAWS OF MOTION
S# Correct Assertion Correct Reason
4.1 INTRODUCTION; 4.2 ARISTOTLE’S FALLACY
Objects at rest need external force to start Initiating motion (kicking a ball, throwing a stone) requires
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moving. applying force.
Stopping a moving object requires external force. Applying force against its motion halts the object (e.g.,
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stopping a rolling ball).
Force can act on objects with contact or at a Gravity (falling object) and magnetism (magnet attracting
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distance. nail) demonstrate both.
Uniform motion doesn't require constant external A skater on frictionless ice exemplifies this scenario.
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force.
Aristotle believed constant external force is His explanation involved air continuously pushing a flying
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needed for motion. arrow.
Friction challenges Aristotle's view on Friction opposes motion, eventually stopping the object
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maintaining motion. (child's toy car).
Friction necessitates continuous external force The child pulling the toy car counteracts friction to
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for uniform motion. maintain motion.
Without friction, uniform motion persists without The toy car example suggests this possibility in a
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external force. frictionless environment.
4.3 THE LAW OF INERTIA
Objects in motion stay in motion with constant Galileo's inclined plane experiments show this - motion
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velocity (ideally frictionless). continues on a frictionless plane.
Objects at rest stay at rest absent external forces. Inertia applies to both motion and rest - zero net force
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means no change in state.
Inertia is an object's tendency to resist changes Explains why a moving object keeps moving and a
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in its motion state (rest or constant velocity). stationary object stays still.
Aristotle believed constant external force is This contradicts inertia - objects in motion can maintain
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needed for sustained motion. constant velocity without constant force.
Friction opposes inertia, slowing and eventually Friction creates a net opposing force, gradually reducing
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stopping a moving object. the object's velocity.
4.4 NEWTON’S FIRST LAW OF MOTION
Inertia is an object's tendency to resist changes Explains why an object stays still or keeps moving at a
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in its motion state (rest or constant velocity). constant speed unless acted upon by an external force.
A stationary object remains at rest due to inertia. Inertia prevents motion change (staying at rest) without an
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external push or pull.
A moving object maintains constant velocity due Inertia prevents motion change (maintaining constant
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to inertia. velocity) without an external push or pull.
Net external force is zero when an object is at Inertia dictates this - no change in motion requires no net
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rest or in constant motion. external force.
Friction opposes inertia, eventually stopping a Friction creates a net opposing force, slowing the object
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moving object. down until it stops.
A coasting spaceship experiences zero net force Inertia aligns with this - no net force means no
19 and maintains constant velocity (evidence from acceleration, so the object keeps moving at the same
space travel). speed.
Unlike internal forces, external forces can change Internal forces cause internal rearrangement, not a change
20 an object's motion state. in overall motion (different from external push/pull).
4.5 NEWTON’S SECOND LAW OF MOTION
Momentum captures the combined effect of an It's the product of mass (inertia) and speed, influencing
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object's mass and velocity. how much force is needed to change its motion.
A more massive object requires a greater net Mass is a measure of inertia, an object's resistance to
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A higher speed necessitates a stronger opposing A faster object has greater momentum, requiring a larger
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force for the same stopping time. force to overcome it in a specific time frame.
The rate of momentum change determines the A quicker change in momentum necessitates a greater
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force needed. applied force.
The second law applies to both the direction and Force can alter the direction of momentum along with its
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magnitude of momentum change. speed.
The second law applies to a single particle, a This concept is valid beyond simple objects, extending to
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rigid body, or a system of particles. complex systems as well.
The force acting at a specific moment dictates the An object's past motion is irrelevant; the current force
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acceleration at that instant. determines the current acceleration.
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