Physics 1050 Lecture 2 Notes

Course Platforms and Access

• There are two similarly-looking sites for this course with different purposes:
  • UVA Canvas site for 1050: access to syllabus, gradebook, Piazza, lecture slides and videos.
  • WileyPLUS site for 1050: access to textbook, pre-quizzes, homework, practice problems.
• You will need access to both.
• WileyPLUS setup:
  • Go to http://www.wileyplus.com/go/login.
  • Click “Sign up now” to create an account.
  • Enter course section ID B01614 (PHYS 1050 - Fall 2025) to find your course and complete registration.
• Piazza (for questions outside of lecture):
  • Access at https://piazza.com/virginia/fall2025/phys1050/home
  • Or access Piazza from the left-side toolbar in Canvas to post questions and browse answers.
• Poll Everywhere (real-time lecture responses):
  • Go to pollev.com/chrisneu and follow online instructions.
  • You will be asked to authenticate via the virginia.edu SSO, then create a Poll Everywhere account.
  • Use your primary virginia.edu email address when creating your Poll Everywhere account (e.g., mst3k@virginia.edu).
• WileyPLUS course ID: B01614
• Optional quick access: PollEv.com/chrisneu or scan the QR code provided in materials.
• Note: These tools support different aspects of the course (textbook vs. interactive questions vs. class-wide discussions).

Tutorial Sessions and Note-Taker Opportunity

• Learning Assistants (LAs) for this class:
  • Itzal De Urioste Terrazas
  • Juliette Steffensen
  • Lihong Yao
• LAs will hold tutorial sessions (timing still To Be Confirmed).
• Volunteer note-taker opportunity:
  • Scan daily notes and send a PDF to the instructor.
  • Several doc scanning apps are available; not a heavy burden.
  • If interested, contact the instructor directly.
• If you can’t attend tutorial sessions or office hours:
  • Use Piazza to pose questions.

Reminders

• Please complete the pre-semester questionnaire if not yet done (sample numbers shown: 113 out of 135 so far).
• Course communications will come via email:
  • Announcements posted to Canvas site
  • Emails to your virginia.edu Inbox
• Do not opt out of receiving messages; check your Inbox regularly for communications about this course and others.

Skating: The Main Topics Today

• Inertia
• Position
• Velocity and speed
• Force
• Acceleration (speeding up, slowing down, changing directions)
• Mass
• Newton’s First and Second Laws

Skating: Conceptual Illustration

• Skating on ice can appear magical: a person on skates can stand stationary, then initiate motion without an external push, glide at a steady speed with nothing pushing them, and continue gliding until they stop.
• Real discussion points:
  • Why does a skater start to move?
  • Why does a skater keep moving?
  • Why does a skater stop?
  • Could a skater travel forever?
• Note: This is a everyday-physics scenario to illustrate inertia and forces, not magic.

Definitions: Speed and Velocity

• Speed
  • A measure of how far an object travels in a given time.
  • Units: \,m/s\ (meters per second).
  • Instantaneous speed: speed at a particular moment (e.g., a car speedometer).
  • Average speed: total distance divided by total time.
• Velocity
  • A measure of how far an object travels in a given direction in a given time.
  • Units: \,m/s\ in a specific direction (e.g., m/s due north).
• Steady velocity: moving in a straight line at a constant speed (no speeding up or slowing down).
• Acceleration: any change in velocity (speed, direction, or both).
  • Acceleration is a vector quantity.
  • If velocity changes, the object experiences acceleration.

Case Studies: Speed and Velocity

• Case 1 (Case 1): Skater gliding straight East for 5 seconds, traveling 1 m each second.
  • Total distance after 5 s: 5 m
  • Average speed: 5 m / 5 s = 1 m/s
  • Instantaneous speed throughout: 1 m/s
  • Velocity: 1 m/s East (constant both magnitude and direction)
  • Conclusion: This is a case of steady velocity.
• Case 2 (Case 2): After 5 seconds, the skater turns North and continues for another 5 seconds, still at 1 m per second.
  • Total distance after 10 s: 10 m
  • Average speed: 10 m / 10 s = 1 m/s
  • Instantaneous speed: 1 m/s throughout
  • Velocity: not constant due to change in direction (east then north)
  • Conclusion: Not a case of steady velocity – velocity is a vector and changes direction.

Inertia and Newton’s First Law (N1L)

• Inertia: resistance of any object to changes in its motion.
  • In the absence of external influences, an object at rest stays at rest, and a moving object keeps moving at a constant velocity.
  • Inertia is a property of every object; the amount of inertia is quantified by the object's mass.
• Newton’s First Law (N1L): An object free of external influences moves in a straight line with constant speed (i.e., at constant velocity).
• Context note: Inertia is foundational for understanding how forces relate to motion.

Forces and Vector Sums

• A force is a push, pull, or pivot that influences motion.
• A force is a vector quantity; direction matters.
• Objects can experience multiple forces simultaneously.
• Net force: the vector sum of all individual forces acting on the object.
  • Net force determines the resultant acceleration.
• Restatement of N1L: An object not subject to outside forces moves at constant velocity; stationary is a special case of constant velocity (velocity = 0).

Fundamental Lesson of Physics 1060

• If an object speeds up, slows down, or changes direction, it must be experiencing a force.
• The applied force on an object has a magnitude and a direction.
• The magnitude of the applied force is proportional to the change in the object's speed.
• The direction of the applied force depends on the change in trajectory.
• A change in speed or trajectory is called acceleration (a vector quantity).

Back to the Skater: Starting and Stopping

• Starting from rest: if there is a net force on the skater, they will start to move in the direction of that net force.
• Gliding with a net force opposite to motion: the skater will slow and stop.
• Both starting and stopping involve a change in velocity (acceleration).
• Acceleration is a vector, denoted as
  • $\boldsymbol{a}$
  • Represents a change in either the magnitude or the direction of velocity, or both.

Acceleration, Force, and Mass (Newton’s Second Law)

• A net applied force causes acceleration.
• Inertia reflects an object’s resistance to a change in velocity; mass quantifies inertia.
• Relationship (Newton’s Second Law):
  • Vector form: $\boldsymbol{a} = \frac{\boldsymbol{F}}{m}$
  • Equivalent (often used): $\boldsymbol{F}_{net} = m \boldsymbol{a}$
• Implications:
  • More mass -> more inertia -> greater resistance to acceleration for a given net force.
  • Less mass -> less inertia -> easier to accelerate for a given net force.

Demonstrations of Inertia (references on the slides)

• Inertia demonstrations shown in class materials:
  • Bottle & Pencil
  • Tablecloth Pull #1
  • Hanging Masses
• These demonstrations illustrate how inertia resists changes in motion when external forces are removed or redistributed.

Tablecloth Demonstration: Questions to Consider

• What forces are present on the plate, cutlery, wineglass, and tablecloth?
• Why do the plate, cutlery, and wineglass stay largely stationary when the tablecloth is jerked away?
• How does the observed behavior relate to inertia?

What Comes Next

• To do:
  • Complete the pre-semester survey (example: 113/135 responses so far).
  • Register for WileyPLUS, Piazza, and Poll Everywhere if not yet done.
  • Do the readings for next week.
  • PQ1 due Monday, 1 Sept at 1pm.
• Reminders:
  • Office hours: Wed, Fri 2–3 pm in Physics 045.
  • LA optional tutorial sessions: day/time/location TBD.
  • See Online Meetings area in the left-hand sidebar for Zoom details.
  • If you can’t attend office hours or Tutorial Sessions, post questions on Piazza.
• Extra note for the UVA community:
  • The slide content includes a campus event teaser: UVA football vs. Coastal Carolina, Saturday kickoff at 6 pm.