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PhysicsChapter Two - Kinematics
Presented by: Taylor Ripke
Mechanics- Study of Motion Kinematics- Mechanics of Objects
**Assume no rotation** Ex. Cars, Atoms, Planes
Section 2.2 - Kinematics
Position Vector – Where it is Denoted by: r Changes as a function of time r = r (t)
Position and Displacement Vectors
Definition: Difference between final position vector and initial position vector
∆r = r2 – r1
∆r means “difference or change in”
Displacement
**Not the same as Displacement** Recall displacement- how far from origin Definition: Absolute value of the displacement
vector “How far you’ve traveled” Δr = |r1| + |r2|
Distance
Your dorm room is located 0.25 mi from the dairy store. You walk from your room to the Dairy Store and back. Which of the statements is true:
a) The distance is 0.5 mi and displacement is 0.5 mi.
b) The distance is 0.5 mi and displacement is 0.0 mi.
c) The distance is 0.0 mi and displacement is 0.5 mi.
Example
Example ContinuedHome Dairy Store0.25mi
Displacement = ∆r = r2 – r1 = 0.25 – 0.25 = 0mi
Distance = Δr = |r1| + |r2| = |0.25| + |0.25| = 0.5mi
If ri = rf, displacement is 0.
Displacement = How far from origin
Distance = Total ground covered
Key Points
Section 2.3 - Velocity Average velocity – Vx = Instantaneous velocity – V = Speed – absolute value of velocity
Velocity – a vector with direction
**Speed is never negative**
Speed = |v| = |vx|
Average speed = v =
“ ” 𝑙 being distance
Equations
Suppose a swimmer completes the first 50m of the 100m freestyle in 38.2s. She then turns around and swims back in 42.5s.
Question: What is the average velocity and average speed for the first leg?
Example
Vx = = = = 1.31
Average velocity = 1.31Speed is the absolute value = |1.31| = 1.31
Solution
Average acceleration – defined as the velocity change per time interval
ax =
Instantaneous acceleration – defined as the limit of the average acceleration as the time interval approaches 0.
Acceleration
Graph Representations
Average Velocity/Acceleration
Instantaneous Velocity/Acceleration
I.
Fundamental Kinematic Equations
Assuming a constant acceleration of ax = 4.3 m/s2, starting from rest, what is the airplane’s take off velocity after 18.4s?
Example
I. Find an equation
II. At Rest
III. Acceleration
IV. Time
Solution
Displacement – how far from origin Distance – how far you’ve traveled Velocity – vector with direction Speed – absolute value of velocity Acceleration – velocity change with time
Recap
• Campus Party Brasil, “Michio Kaku” February 11, 2012 via Flickr, Attribution-ShareAlike
• Ed Schipul, “Bill Nye” October 21, 2010 via Flickr, Attribution-ShareAlike
• Bauer, W., & Westfall, G. (2014). University physics (Second ed.). New York, NY: McGraw-Hill.
References