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External Force Impact
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- The second law of motion specifies that an unbalanced external force on an object results in a change in its velocity, producing acceleration.
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Everyday Observations
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- A table tennis ball doesn’t hurt a player when hit, but a fast-moving cricket ball can.
- A stationary truck isn’t a threat, but a moving one can be fatal.
- A bullet, though small in mass, can be deadly when fired.
- These observations highlight that the impact produced by objects depends on their mass and velocity.
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Greater Force Required
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- To accelerate an object, a greater force is necessary to achieve a higher velocity.
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Momentum
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- Newton introduced momentum, denoted by p, defined as the product of an object’s mass (m) and velocity (v):
p = mv
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- Momentum has both magnitude and direction. Its direction coincides with the velocity.
- Its SI unit is kilogram-metre per second (kg ms-1).
- An unbalanced force leads to a change in the object’s momentum.
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Example of a Car With a Dead Battery
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- A sudden push doesn’t start it, but a continuous push over time accelerates it to a speed that can start its engine.
- This implies that momentum change is influenced by both the force magnitude and the duration it’s applied.
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Momentum Change
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- The second law of motion posits that the rate of change of momentum of an object is proportional to the applied unbalanced force and occurs in the direction of this force.
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