Classical mechanicsLesson 1 of 6 in the course Newton's Laws of Motion

Forces: Classification, Free-Body Diagrams, and Vector Addition

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

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Summary

This lesson distinguishes describing motion from explaining what causes it. It also introduces the range in which Newton’s laws provide a reliable description of nature.

Kinematics describes how objects move, including their position, velocity, and acceleration. It does not focus on the causes of that motion.

Dynamics studies how forces affect the motion of objects and systems. A system is any object or collection of objects selected for analysis. For example, kinematics can describe a ball’s changing velocity, while dynamics asks what forces caused that change.

All flashcards

Force
A push or pull with magnitude and direction; it is a vector quantity.
Contact force
A force that arises from direct physical contact between objects.
Field force
A force that acts without direct contact through a field.
External force
A force that originates outside the object or system being analyzed.
Free-body diagram
A sketch showing all external forces acting on one selected object or system.

Quiz questions

  1. Earth's gravitational pull acts on an object without direct physical contact. What type of force is it?Answer: A field force
  2. A book rests on a table. Which forces belong on a free-body diagram of the book?Answer: Earth's downward gravitational force and the table's upward contact force
  3. Which situation is generally well described by Newtonian mechanics?Answer: A baseball moving at an ordinary speed
  4. At a fundamental level, what interaction gives rise to ordinary contact forces between objects?Answer: Electromagnetic interactions between atoms
  5. Two forces are F⃗1=3.0i^+8.0j^ N\vec{F}_1=3.0\hat{i}+8.0\hat{j}\,\text{N} and F⃗2=5.0i^+4.0j^ N\vec{F}_2=5.0\hat{i}+4.0\hat{j}\,\text{N}. What is their vector sum?Answer: 8.0i^+12.0j^ N8.0\hat{i}+12.0\hat{j}\,\text{N}

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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