1 / 0

Dynamics: Cause of Motion

Dynamics: Cause of Motion. Sections 7.1 , 7.2. Reminders…. 10-point In-class Quiz #4 on Tuesday, Feb 27, addressing inertia, momentum, NI, and NII Next reading quiz due prior to class on Thursday LAB A4-PM: Projectile Motion due Friday 4pm Midterm grades posted on March 2.

liz
Download Presentation

Dynamics: Cause of Motion

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Dynamics: Cause of Motion

    Sections 7.1 , 7.2
  2. Reminders… 10-point In-class Quiz #4 on Tuesday, Feb 27, addressing inertia, momentum, NI, and NII Next reading quiz due prior to class on Thursday LAB A4-PM: Projectile Motion due Friday 4pm Midterm grades posted on March 2. Test #2 on Tuesday, March 4 addressing all sections since Examination #1 (Chapters 4, 6, & 7) Final Exam Monday, May 5, 7:50 a.m.
  3. Conservation of Momentum Demonstration: the total momentum of an isolated system is conserved. That is, pi = pfif and only if we have an “isolated system” – no unbalanced outside forces. Example 1 – the collision of carts Example 2 – the “explosion” of carts Numerical problems…
  4. Numerical Problem 1 A truck with a mass of 3,000kg and a velocity of +20m/s collides head on with a car of 1,500kg mass and a velocity of -20m/s. If the vehicles stick together, what is the resulting motion of the pair? Solve using conservation of momentum; that is, pi = pf.
  5. Numerical Problem 2 A train car (mass 11,200kg) is moving along at a speed of +2m/s. A 5,000kg mass of coal with no horizontal motion is dropped into the hopper of the train car. What is the resulting motion of the train car now loaded with coal?
  6. The Second Law of Motion a.k.a. Newton’s Second Law The net instantaneous force acting on an object is precisely the instantaneous change of its momentum per unit time. In symbols, the second law can be written as F = Δp/Δt with Δt very small. Note that F and Δp are vectors. Not very enlightening; time for an experiment.
  7. Newton’s Second Law Experiment: Acceleration as a function of force (constant mass system) Acceleration as a function of mass (constant force system) Results: a is proportional to F a is inversely proportional to m Conclusion: F = kma; k=1 if F defined properly
  8. Second Law Reprise F = Δp/Δt F = Δmv/Δt F = mΔv/Δt F = ma Both F and a are vectors; m is a scalar. The sum of forces acting on a body produce an acceleration inversely proportional to mass. ΣF=ma (where F is expressed in Newtons)
  9. 2nd Law Problem – Examples An car with a mass of 1,500kg accelerates at a rate of -2m/s2 under a constant force. What are the magnitude and direction of that force? How much force would it take to slow a 75kg person riding in a car going +20m/s to a complete stop if the time was 0.03 seconds – the typical time of an auto collision?
  10. More Examples of Newton’s 2nd Law An object accelerates at a rate of 1.5m/s2 under a force of 53N. What is its mass? How much upward force does the ground apply to someone with a mass of 75kg to counter balance the pull of gravity? Note that g = -9.8m/s2 and that Fnet = ma and that a = g.
More Related