 # Acceleration 1D motion with Constant Acceleration Free Fall Lecture 04 (Chap. 2, Sec. 6-10 ) General Physics (PHYS101) Sections 30 and 33 are canceled.

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Acceleration 1D motion with Constant Acceleration Free Fall Lecture 04 (Chap. 2, Sec. 6-10 ) General Physics (PHYS101) Sections 30 and 33 are canceled and became section 27

Lightning Review Displacement - change of position Average velocity - displacement over time interval Instantaneous velocity - the same but for very small time interval Last lecture:

Average Acceleration Average acceleration is the rate of change of the velocity Changing velocity (non-uniform) means an acceleration is present Average acceleration is a vector quantity (i.e described by both magnitude and direction) SI unit: m/s 2

Instantaneous Acceleration Instantaneous acceleration is the limiting case of the average acceleration as the time interval goes to zero.

Graphical Interpretation of Acceleration Average acceleration is the slope of the line connecting the initial and final velocities on the velocity-time graph Instantaneous acceleration is the slope of the tangent to the curve of the velocity-time graph for the given value of time

1D motion: uniform velocity Uniform velocity (shown by red arrows maintaining the same size) Acceleration equals zero

1D motion: constant (positive) acceleration Velocity and acceleration are in the same direction Acceleration is uniform (blue arrows maintain the same length) Velocity is increasing in time (red arrows are getting longer)

1D motion: constant (negative) acceleration Velocity and acceleration are in opposite directions Acceleration is uniform (blue arrows maintain the same length) Velocity is decreasing (red arrows are getting longer)

1D motion: constant acceleration Our job: to find the equation for the position and velocity of the object to make predictions!

10 1D motion with constant acceleration Recall that We know that We find v t v0v0 Since x t x0x0

11 1D motion with constant acceleration

12 Summary of kinematic equations: 1D motion acceleration is constant displacement as a function of velocity and time displacement as a function of time velocity as a function of time velocity as a function of displacement average velocity Displacement as a function of velocity

13 Free fall - 1D motion with constant acceleration

14 Free fall - 1D motion with constant acceleration 0 x 1 2 3 0 y 1 2 3 All objects moving under the influence of only gravity are said to be in free fall All objects falling near the earth’s surface fall with a constant acceleration This acceleration is called gravitations acceleration, indicated by g and always points perpendicular to the earth’s surface y

15 acceleration displacement vs velocity and time displacement vs time velocity vs time velocity vs displacement average velocity displacement vs velocity Free fall - 1D motion with constant acceleration

16 Case 1: zero initial velocity y

17 Case 2: NONzero initial velocity y y Case 1 Case 2

18 Case 3: object thrown upward

19 Case 4: object thrown upward

Free fall Mass does not matter, if the air resistance is neglected

21 Positive acceleration

22 Negative acceleration

23 1D motion with constant acceleration Example 1: A car is traveling with a constant speed v 0. At some time, the driver puts on the brakes, which slows the car down at a rate of a. Find:  how much farther does the car travel for time t f, before it stops completely.  low long does it travel if the stopping distance is x f. Given: v 0 =v 0 a=-a x 0 =0 t 0 =0 v=0 Find: 1) x f =?, knowing t f. 2) t f =?, knowing x f.

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