Newton's Laws of Motion: 18 flashcards
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1. State Newton's first law of motion.
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An object remains at rest or in uniform motion in a straight line unless acted on by a net external force.
2. What is inertia?
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The tendency of an object to resist changes in its state of motion; it depends on mass.
3. What is another name for Newton's first law?
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The law of inertia.
4. Write Newton's second law as an equation.
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$\vec{F}_{net} = m\vec{a}$
5. How is acceleration related to net force and mass?
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Acceleration is directly proportional to net force and inversely proportional to mass.
6. What is the SI unit of force, and how is it defined?
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The newton (N): $1\,\text{N} = 1\,\text{kg}\cdot\text{m/s}^2$, the force giving a $1\,\text{kg}$ mass an acceleration of $1\,\text{m/s}^2$.
7. State Newton's third law of motion.
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For every action force, there is an equal and opposite reaction force.
8. Why don't action and reaction forces cancel each other out?
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They act on different objects, so each object feels only one force of the pair.
9. What must you find before applying $F = ma$?
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The net force — the vector sum of all forces acting on the object.
10. Why do seatbelts protect passengers?
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Because of inertia (first law): your body keeps moving forward when the car stops, and the belt provides the force to decelerate you.
11. How does a rocket move in space?
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It expels gas downward; the gas pushes the rocket upward with an equal and opposite force (third law).
12. If net force doubles while mass stays fixed, what happens to acceleration?
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Acceleration doubles.
13. If mass doubles while net force stays fixed, what happens to acceleration?
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Acceleration halves.
14. Which law describes zero net force, and which quantifies nonzero net force?
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The first law describes zero net force; the second law quantifies nonzero net force.
15. Under what conditions are Newton's laws accurate?
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When speeds are much less than the speed of light and gravity is not extreme.
16. How does walking depend on Newton's third law?
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You push the ground backward, and the ground pushes you forward with an equal and opposite force.
17. Why does a loaded truck need a longer braking distance than a bicycle at the same speed?
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It has more mass and therefore more inertia, so it resists changes in motion more strongly.
18. In $\vec{F}_{net} = m\vec{a}$, why does direction matter?
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Because force and acceleration are vectors: a force pointing left produces acceleration to the left.
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