1 / 14

Understanding Motion

Understanding Motion. Linear Motion. Motion. The motion of an object can only be recognized when something is established as a basis of comparison…a reference point We say an object is moving when its position changes compared to that reference point

redford
Download Presentation

Understanding 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. Understanding Motion Linear Motion

  2. Motion • The motion of an object can only be recognized when something is established as a basis of comparison…a reference point • We say an object is moving when its position changes compared to that reference point • For most day-to-day situations, the Earth, and those things affixed to it, serve as a convenient reference frame.

  3. Position and Time • These are the two most fundamental physical quantities that can be measured to describe an object’s motion. • The relationship between these variables can be discovered experimentally and modeled using mathematics in both graphical and equation form.

  4. Position vs. Time Graphs • The magnitude (size) of the slope tells us… • The algebraic sign of the slope tells us… • The magnitude and sign together tell us… • The vertical intercept tells us… • When this graph is a straight line we know…

  5. Position vs. Time Graphs The generic equation for a linear graph is… y = mx + b In terms of the physical quantities being plotted this becomes… x = mt + b Position, x (m) Time, t (s)

  6. Position vs. Time Graphs If we replace the slope and intercept terms with what they tell us we get… x = vt + xi Where v is the velocity (m/s) and xi is the initial position (m) of the object in motion m = v Position, x (m) xi Time, t (s)

  7. x = vt + xi • This equation (straight line with slope v and intercept xi) is a model that describes the relationship between position and time for an object moving with constant velocity. x = position of object after time, t v = velocity of object (speed in a direction) t = elapsed time xi = starting position of the object

  8. Constantly Accelerated Motion(ball on a ramp) • Position-time graphs are NOT linear, they are quadratic… x  t2 • slope is NOT constant  Velocity is changing • Velocity-time graphs are linear… v  t • Slope is constant  The rate at which velocity is changing is constant SLOPE = ACCELERATION

  9. v = at + vo • This equation is a model describing the relationship between velocity and time for an object that is constantly accelerating v – velocity after time, t a – acceleration t – elapsed time vo – starting velocity

  10. x = ½ at2 + vot + xo • This equation models the relationship between position and time for constantly accelerated motion • This equation emerges from our ball on a ramp data or it could be derived (we will!) x = position after time, t a = acceleration vo = starting velocity t = elapsed time xo = starting position

  11. Free Fall • An object is considered to be in free fall when it is only under the influence of gravity • Objects in free fall near the surface of Earth experience constant acceleration… a = g = 9.80 m/s2 downwards

  12. “Fall” is misleading • An object can be in free fall while it is traveling upwards (only under the influence of g) • Slows down at a constant rate equal to the rate that a falling object gains speed

  13. Free Fall Equations Nothing new here! Free fall is constantly accelerated motion so the kinematics equations are all applicable. Remember a = g = 9.80m/s2 (downward) ***When problem solving, pay close attention to direction of quantities!!!! vavg = x/t a = v/t v = vo + at x = vot + ½ at2 v2 = vo2 + 2a x Often you will find x changed to y when working on vertical motion problems

  14. Sample Problem • A volley ball is hit straight upward with a speed of 6.0 m/s. If the volley ball starts 2.0 m above the floor, how long will it be in the air before hitting the floor?

More Related