Ch. 3 & 4 Motion & Forces

Ch. 11 Motion II. Describing Motion Motion Speed & Velocity Acceleration A. Motion Problem: Is your desk moving? To describe motion completely, we need a frame of reference a

system of objects that are not moving with respect to one another. A. Motion Relative Motion Movement in relation to a frame of reference. Reference point Motion Quick Write Explain a time where you experienced confusion about

your motion. Measuring Distance Distance the length of a path between two points. Units m (meters) km (kilometers) cm (centimeters) Measuring displacement Displacement is independent of the path taken by the object.

Involves the starting point, ending point, and direction. Vector quantity Example: A man travels 4 blocks North and then returns 4 blocks South. What is his displacement? B. Speed & Velocity Speed d rate of motion v t distance traveled per unit time distance speed

time B. Speed & Velocity Instantaneous Speed speed at a given instant Ex. The speed measured by a police officer using a radar gun Average Speed speed over an entire trip total distance avg. speed

total time __ v = d t B. Speed & Velocity Velocity speed in a given direction can change even when the speed is constant! Velocity Problems Graphing d/t

E. Graphing Motion Distance-Time Graph slope A = speed steeper slope = faster speed B

straight line = constant speed flat line = no motion E. Graphing Motion Distance-Time Graph Who started out faster? A (steeper slope) Who had a constant speed? A

Describe B from 10-20 min. B stopped moving A B Find their average speeds. A = (2400m) (30min) A = 80 m/min B = (1200m) (30min) B = 40 m/min Acceleration

C. Acceleration vf - vi a t Acceleration the rate of change of velocity change in speed or direction a v f vi a: acceleration

vf: final velocity t vi: initial velocity t: time C. Acceleration Positive acceleration speeding up Negative acceleration slowing down

Quick Write Given an example of something that you have seen in your daily life that is accelerating. Describe its motion. D. Calculations A roller coaster starts down a hill at 10 m/s. Three seconds later, its speed is 32 m/s.

What is the roller coasters acceleration? GIVEN: WORK: vi = 10 m/s a = (vf - vi) t t=3s vf = 32 m/s a = (32m/s - 10m/s) (3s) a=? vf - vi

a t a = 22 m/s 3 s a = 7.3 m/s2 D. Calculations How long will it take a car traveling 30 m/s to come to a stop if its acceleration is -3 m/s2? GIVEN: WORK: t=? vi = 30 m/s

t = (vf - vi) a t = (0m/s-30m/s)(-3m/s2) vf = 0 m/s a = -3 m/s2 vf - vi a t t = -30 m/s -3m/s2 t = 10 s E. Graphing Motion Distance-Time Graph 400

Acceleration is indicated by a curve on a Distance-Time graph. Distance (m) 300 200 100 Changing

0 0 5 10 Time (s) 15 20 slope = changing velocity

E. Graphing Motion Speed-Time Graph = acceleration +ve = speeds up -ve = slows down slope 3 Speed (m/s) 2 straight

line = constant accel. 1 line = no accel. (constant velocity) flat 0 0 2 4

6 Time (s) 8 10 E. Graphing Motion Speed-Time Graph Specify the time period when the object was... slowing down 5 to 10 seconds speeding up 0 to 3 seconds

3 Speed (m/s) 2 moving at a constant speed 3 to 5 seconds not moving 0 & 10 seconds 1 0

0 2 4 6 Time (s) 8 10