General physicsLesson 1 of 2 in the course Linear Momentum and Collisions

Linear Momentum: Definition, Direction, and Units

5 flashcards · 5 quiz questions · 5 match pairs · 2 fill-in sentences · English

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Summary

Momentum describes an object's motion by combining its mass and velocity. Unlike kinetic energy, momentum also tells us the direction in which an object is moving. This makes momentum useful for comparing moving objects and understanding how difficult their motion may be to change.

Here, mm is the object's mass and v⃗\vec{v} is its velocity. Since mass is a scalar and velocity is a vector, momentum points in the same direction as the object's velocity. For an object moving in one dimension, a chosen positive direction gives momentum a positive or negative sign according to the direction of motion.

All flashcards

What is linear momentum?
Linear momentum is the vector product of an object's mass and velocity, given by p⃗=mv⃗\vec{p}=m\vec{v}.
Why does momentum have a direction?
Momentum has the direction of velocity because mass is a scalar and velocity is a vector.
What is the SI unit of momentum?
The SI unit is the kilogram-meter per second, written kg⋅m/s\text{kg} \cdot \text{m/s}.
How does momentum differ from kinetic energy?
Momentum is a vector that includes direction and equals mv⃗m\vec{v}. Kinetic energy is a scalar, equals 12mv2\frac{1}{2}mv^2, and does not indicate direction.
How can a slower object have more momentum than a faster one?
Momentum depends on both mass and velocity. A sufficiently massive object can have greater momentum despite moving more slowly.

Quiz questions

  1. How is an object's linear momentum defined?Answer: As the product of its mass and velocity: p⃗=mv⃗\vec{p}=m\vec{v}.
  2. Why is momentum a vector quantity?Answer: Velocity has magnitude and direction, while mass is scalar.
  3. What is the SI unit of linear momentum?Answer: kg⋅m/s\text{kg} \cdot \text{m/s}
  4. Two objects have equal masses and equal speeds but move in opposite directions. How do their momentum vectors compare?Answer: They have equal magnitudes and point in opposite directions.
  5. A fast, light object has less momentum than a slower, massive object. What best explains this?Answer: The greater mass more than compensates for the lower speed.

Based on University Physics Volume 1 by William Moebs, Samuel J. Ling, Jeff Sanny (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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