PHYSICS 11 TODAY Acceleration Grading Scale for Physics

PHYSICS 11 TODAY: • Acceleration

Grading Scale for Physics 11 might change) 2013/2014 Assignments (worksheets, labs, homework, pop-quizzes) Quizzes (around 25 of them) Unit Tests (7 of them – 5% each) Projects (posters, ppt presentations, research etc. . ) Final Exam 15% 20% 35% 10% 20% (it

Letter Grades for Physics 11 might change) 2013/2014 A B C+ C D F 100% – 86% 85% – 73% 72% – 67% 66% – 60% 59% - 50% 49% - under (it

2. 2 ACCELERATION

2. 2 ACCELERATION Imagine a train speeding up or slowing down… WHAT HAPPENS TO ITS VELOCITY? ? Whenever velocity changes:

2. 2 ACCELERATION

3. 2 ACCELERATION

ACCELERATION SI Units: meters per second square (m/s 2) It has DIRECTION and MAGNITUDE

Find the acceleration of an amusement park ride that falls from rest to a speed of 28. 0 m/s in 3. 0 s HINT: from “rest” means (vi = 0 m/s) “comes to rest” means (vf = 0 m/s) 9. 3 2 m/s

Velocity has two aspect to it: Speed Direction Acceleration can occur under 3 conditions:

When… 1. Speed changes 2. Direction changes 3. Speed and Direction change

1. Speed changes The object is speeding up The object is slowing down vf > v 0 vf < v 0

1. Speed changes The object is speeding up

1. Speed changes The object is slowing down

2. Direction changes If direction changes, velocity changes because:

3. Speed and Direction change

Practice Problems: 2. 2. 1 (pg. 49) - 15. 0 2 m/s The car is slowing down…

Negative ACCELERATION Is an object speeding up OR slowing down? OR

Homework Textbook: pg. 49 – PRACTICE B (1 – 5)

Magnitude and Direction of Acceleration Imagine a train moving to the right… What can you say about displacement and velocity? STATION 1 STATION 2 displacement is positive velocity is positive

Magnitude and Direction of Acceleration Case #1: Imagine a train going with no speeding up, or stopping = at a constant velocity What can you say about velocity and acceleration? STATION 1 STATION 2 velocity is not changing, therefore Δv is 0 m/s acceleration is zero because velocity is constant

Magnitude and Direction of Acceleration Case #2: Imagine a train speeding up as it moves to the right … STATION 1 STATION 2

Magnitude and Direction of Acceleration Case #2: Imagine a train speeding up as it moves to the right … What can you say about velocity? STATION 1 STATION 2 velocity’s magnitude increases (from 5 m/s to 10 m/s) so Δv will be positive

Magnitude and Direction of Acceleration Case #2: Imagine a train speeding up as it moves to the right … What can you say about acceleration? STATION 1 STATION 2 acceleration will be positive because the change in velocity (Δv) is positive

Magnitude and Direction of Acceleration Case #3: Imagine a train going in the positive direction, direction but it is slowing down (not stopping) as it approaches the next station STATION 1 STATION 2 What can you say about displacement, velocity, change in velocity and acceleration?

Magnitude and Direction of Acceleration Case #3: Imagine a train going in the positive direction, direction but it is slowing down as it approaches the next station STATION 1 STATION 2 displacement is positive because Δx (xf – xi) is > 0

Magnitude and Direction of Acceleration Case #3: Imagine a train going in the positive direction, direction but it is slowing down as it approaches the next station STATION 1 STATION 2 velocity is still positive (for example: vi = 10 m/s and vf = 2 m/s) but Δv is negative (vf – vi) is < 0

Magnitude and Direction of Acceleration Case #3: Imagine a train going in the positive direction, direction but it is slowing down as it approaches the next station STATION 1 STATION 2 Because Δv is negative acceleration is also negative

Magnitude and Direction of Acceleration Case #4: Imagine a train going in the negative direction, direction and it is speeding up as it approaches the next station STATION -1 STATION 1 velocity is negative (for example: vi = - 2 m/s and vf = - 10 m/s) and Δv is negative (vf – vi) is < 0

Magnitude and Direction of Acceleration Case #4: Imagine a train going in the negative direction, direction and it is speeding up as it approaches the next station STATION 1 STATION 2 Because Δv is negative acceleration is also negative Notice: acceleration is negative and the object is speeding up!

Magnitude and Direction of Acceleration Case #5: Imagine a train going in the negative direction, direction and it is slowing down as it approaches the next station STATION -1 STATION 1 velocity is negative (for example: vi = - 10 m/s and vf = - 2 m/s) and Δv is positive (vf – vi) is > 0 (!!)

Magnitude and Direction of Acceleration Case #5: Imagine a train going in the negative direction, direction and it is slowing down as it approaches the next station STATION 1 STATION 2 Because Δv is positive acceleration is also positive Notice: acceleration is positive and the object is slowing down!

SUMMARY Speeding up Slowing down

Think About it… When Scott is out for a bike ride, he slows down on his bike as he approaches a group of hikers on a trail. Explain how his accelaration can be positive even though his speed is decreasing If Scott is moving in the NEGATIVE direction vi = -10 m/s vf = -5 m/s Slowing down

The slope of the graph of velocity (speed) vs. time is the average acceleration Slope of velocity (speed) vs time graph = acceleration The equation for the line (y = mx +b) will have form: v = a·t + (y – intercept) v = 69 t + 7. 0

The slope of the graph of velocity (speed) vs. time is the average acceleration Point A The slope at that The velocity in the point is positive = positive direction is acceleration is increasing POSITIVE (E. g. train just left the station and its speed is increasing)

The slope of the graph of velocity vs. time is the average acceleration The slope at that point is zero = acceleration is ZERO Point B The velocity is constant (E. g. train is moving with out any change in velocity

The slope of the graph of velocity vs. time is the average acceleration The slope at that point is negative = acceleration is NEGATIVE Point C The velocity is decreasing over time (E. g. train is approaching a station, and it is slowing down

HOMEWORK 2. 2 Review Questions PAGE: 52 - 53 PROBLEMS: 1, 3, 5 39

Velocity vs. Time graph Area Under the Curve = Acceleration vs. Time graph Area Under the Curve =

Graphing Practice Handouts 41

QUIZ Thursday? 42