PH 201

1. PH 201 Dr. Cecilia Vogel Lecture 1

2. OUTLINE • Motion in 1-D • position • displacement • velocity • speed

3. -3 -2 -1 0 1 2 3 Motion Along a Line • Like a number line. • Position of object is where it is on the number line • Choose an origin – zero position • Choose a positive direction • Forexample, position is positive when object is to right of origin

4. -3 -2 -1 0 1 2 3 Displacement • Displacement is change in position. • final position – initial position:Dx = xf - xi • Object’s displacement is positive if • final position > initial position • object moved in the positive direction Positive displacement: Negative displacement: from -3 to -1 from 1 to 3 from -1 to -3 from 3 to 1

5. -3 -2 -1 0 1 2 3 More on Displacement • Displacement only depends on xf & xi • Doesn’t matter what happens in between • Ex: Object moves from -1 to -3 then to 0. • Overall displacement is 0-(-1) = +1 • Displacement may be positive even tho part of the motion is in the negative direction.

6. -3 -2 -1 0 1 2 3 More on Displacement • Displacement only depends on xf & xi • Doesn’t matter what happens in between • Ex: Object moves from -1 to +3 then to -1. • Overall displacement is (-1)-(-1) = 0 • Displacement of zero does not mean the object didn’t move.

7. Instantaneous Speed and velocity • Instantaneous speed is how fast object is going at an instant in time • Always positive • Instantaneous velocity is speed and direction • (instantaneous) speed =the magnitude of the (instantaneous) velocity.

8. Summary • Positive velocity • Moving forward • Value of position, x, increasing • Slope of x vs. t is positive • Negative velocity • Moving backward • Value of position, x, decreasing • Slope of x vs. t is negative • Zero velocity • Stopped (maybe just for an instant) • Occurs any time motion changes direction • x vs. t graph is horizontal (maybe just for an instant)