1 Constant & Changing Motion

2 Reference Point A fixed point from which direction is defined. The reference point can be anything. Position Where something is, relative to the reference point.

Scalarand Vector Scalar- has an amount or magnitude. It is always postive Vector- has magnitude and direction. Can be positive or negative 3

4 Distance The length traveled measured from start to finish. Scalar quantity. Has magnitude only Use meters!!!

5 Example #1 A car drives 4 meters north, 3 meters south, then 5 meters north. What’s its total distance driven? D = 4m + 3m + 5m D = 12m

6 Displacement The net difference between the starting point and the ending point.  d = d final – d initial

7 Example #2 A car drives 4 meters north, 3 meters south then 5 meters north. What’s its displacement? Δd = 9m north – 3m south Δd = 6m north !

8 Speed Total distance traveled divided by the total time elapsed. Speed represents the magnitude of velocity (scalar quantity) speed = distance/time absolute valueSpeed is the absolute value of velocity. positiveIt is always a positive value. SpeedSpeed is the magnitude of velocity.

9 Average Velocity ( V avg ) Velocity is a vector quantity (magnitude & direction) Total distance traveled divided by the total time elapsed. V avg =  d/  tUnits: m/s

10 Average Velocity 1 mile2 miles 3 seconds1 second2 minutes home Dairy Queen 4 hr. EXXON 3 hr. 5 miles Δt includes ALL time, whether you were moving or not! Δt = 1 sec sec sec sec + 3 sec Δt = sec (x 1 hr / 3600 sec = 7.03 hr) V avg = 5 mi / 7.03 hr V avg = 0.71 mi/hr LHS

11 Instantaneous Velocity (V) Velocity at one point Δd and Δt are very, very, very, very……small!

12 Constant Velocity If a body is moving at a constant velocity, the velocity never changes between intervals. Doesn’t happen often in real life! Ex: V = 10 m/s

13 Acceleration Acceleration is the change in velocity over time. Average acceleration (a avg ) = change in velocity time spent a avg = ΔV / Δt Units: (m/s)m ss 2

14 Acceleration Example #1 Find a avg. V i = 10 m/sV f = 40 m/s a avg = 40 – 10 m/s 2 s *This means that the object’s velocity increases 15m/s every second! a avg = 15 m/s 2 Δt = 2 sec

15 Acceleration Example #2 Find a avg. V i = 40 m/sV f = 10 m/s a avg = 10 – 40 m/s 2 s *This means that the object’s velocity decreases 15m/s every second! a avg = - 15 m/s 2 Δt = 2 sec

16 Acceleration Example #3 Find a avg. V i = 40 m/sV f = 40 m/s a avg = 40 – 40 m/s 2 s *This means that the object’s velocity is constant! a avg = 0 m/s 2 Δt = 2 sec

17 Four Basic Equations of Physics Conditions: –One-dimensional motion –Constant acceleration

18 Four Basic Equations of Physics V f = V i + at d = V i t + ½ at 2 2ad = V f 2 – V i 2 V f + V i 2 d =t