Frames of Reference

 Displacement is a _______________ line distance between where something ______________ and where it ends.  Average velocity is displacement divided by the _______ during which the displacement occurs.  Acceleration is the _____________ in an object’s  _________ divided by the time during which this occurs.

 All motion is relative.  Relative to what? Let’s see.

GROUND 30 m/s 

SOLAR ORBIT 1000 miles / hour--east

GALACTIC ORBIT miles / hour around Sun

OBSERVER BEYOND GALAXY miles / hour around Milky Way

BEYOND THAT?

 Now, we often assume the ground to be our reference frame, but be aware that others can and do exist.

 Every complete description of velocity includes its relation to some frame of reference.

1. Suppose a car travels at a constant 12 m/s relative to the ground. What distance does it cover in 1.0 hour?

 Solution: x v = --- so, t x = v. t = = m 12 m1.0 hr60 min60 s s hr min

 A train leaves the station at the 0.0-m marker traveling at a constant 36m/s. a. How many seconds later will the train pass the m marker?

 Solution: x x v = ---- or, t = ---- t v m t = = 45 s 36m/s

 You accelerate your car from a dead stop. Find your velocity relative to the ground after 6.0 s if your acceleration was 5m/s 2 ?

 Solution: v f - v i a = so v f = v i + at t = 0m/s + (5m/s 2 )(6.0s) = 30m/s