Interpreting Motion

1. Interpreting Motion How to read a Velocity vs. Time graph

2. Velocity vs. Time Graphs v v t t Constant velocity Constant positive acceleration

3. Velocity vs.Time graphs v v t t Constant negative acceleration but object has changed direction (WHY?) Constant negative acceleration

4. If you want to know what the average acceleration is calculate the slope. Slope = Δv / Δt = aave Δv = vf - vi Δt = tf - ti

5. Using slope to predict motion • On a velocity vs. time graph • If slope is 0, then acceleration is 0. The velocity is constant. • If slope is positive, acceleration is constant. • If slope is negative, acceleration is constant in the opposite direction.

6. Is the object changing speed? • You must consider both the direction of the velocity and the direction of the acceleration. • If velocity and acceleration are in the same direction object is speeding up. • If the velocity and acceleration are in opposite direction object is slowing down.

7. Speeding up v Is the velocity positive or negative? +v +a Is the acceleration positive or negative? t 0 -a -v The sign for a and v are the same so both objects are speeding up!

8. Slowingdown (deceleration) v Is the velocity positive or negative? +v -a Is the acceleration positive or negative? t 0 -v +a The sign for a and v are opposite so both objects are slowing down!

9. FindingDisplacement • Equal to the “area under the curve” on a v vs. t graph • Triangle A = ½ b×h • Rectangle A = l×w • Base and length are measured in s. • Height and width are measured in m/s. Area = (m/s)(s) = m

10. V (m/s) Area = l × w length = 3 s width = 50 m/s 50 Δd=150 m 3s ×50 m/s t (s) 1 2 3 4 5 6 7 -25

11. Velocity vs. Time Graphs • The slope of the line tells you the ____________ of the object. • The “area under the curve” represents the change in position or ____________of an object. displacement acceleration

12. pg 93 #13,15-16 and section review #1-2,4 On your own…