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Chapter 11 Motion Key Concepts What is needed to describe motion completely? How are distance and displacement different? How do you add displacement? Frame of Reference To describe motion accurately and completely, a frame of reference is necessary. A system of objects that are not moving with respect to each other. Frame of Reference Relative Motion Relative motion is movement in relation to the frame of reference. Distance Distance is the length of a path between two points. 5m Total Distance is 20m 10m 10m Displacement Distance between two points. Displacement has a magnitude (distance). Displacement also has a direction (north). Displacement is a vector quantity. Straight Line Displacement Displacement is 1.75km To the right 1km .75km Straight Line Displacement Displacement is 0.25km To the right .75km 1km Straight Line Displacement Displacement is 0.25km To the left!!!! 1.25km 1km Distance is 20m 10m 10m Displacement is 14m at an angle of 45° Homework 11-1 Worksheet 11-1 11-1 Assessment: 1-8 Book - Page: 331 Due: 2/2/09 11-2 Key Concepts How are instantaneous speed and average speed different? How can you find the speed from a distance-time graph? How are speed and velocity different? How do velocities add? Motion and Speed Position: A point of reference. Motion: A change of position. Speed(v) Rate at which an object changes position. Speed =(meters/second) v = (m/s) The rate of motion at a given instant. Instantaneous Speed Constant Speed A speed that does not vary. Average Speed Total distance traveled divided by the total time of travel. Total distance Average Speed = total time d v= t Average Speed Oneonta Norwell Calculating Speed Distance {d, meter(m)} Time {t,seconds(s)} Speed {v, meters per second(m/s)} v = d/t Speed Equation d v t Wheel of Answers Find Speed(v) d v t d v= t Find Distance(d) d v t d = vxt Find time(t) d v t d t= v Steps to Solving Problems 1. Read the problem carefully!!! 2. Pick out the information needed to solve the problem. Given 3. What is it that you have to find: Find 4. What equations are needed to solve the problem: Equation Solve Box your answer – units are important!!!! 5. Solve the problem: 6. Example Mr. Clune is traveling to Chatham this weekend. Chatham is approximately 70 miles away. A good estimate of his speed is 50 miles per hour. How long will it take to get there? Given: d = 70 mi v = 50 mi/hr Find: t = ? ? Let’s go to the Wheel of Answers!!!! Equation: Find time(t) d v t d t= v Given: d = 70 mi v = 50 mi/hr Find: t = ? d Equation: t = v 70 mi Solve: t = 50 mi/hr t = 1.4 hr Let’s Practice Page 333 Problems: 1-2 Page 337 Problems: 8-9 Page 351 Problems: 19-20 Due: 2/4/09 Example d = 400 km t = 5 hr Given: d = 400 km t = 5 hr Find: Average Speed (v) = ? Equation: v = d/t Solve: v = d/t v = (400 km) / (5 hr) v = 80 km/hr Velocity Velocity: The speed and direction of an object. (Vector quantity.) 50 km/hr 50 km/hr Graphing Speed Distance(m) 50 D 40 30 B 20 10 C A 10 20 30 40 50 Speed A: Forward B: Zero C: Backward D: Forward Faster than A Time(s) Slope of d vs. t is Speed 50 Distance(m) D 40 30 B C 20 10 A 10 20 30 Time(s) 40 50 Slope of the d vs. t curve Speed!! rise y Slope = run = x distance y = x time = Speed 50 Distance(m) D 40 30 B C 20 10 A 10 20 30 Time(s) 40 50 Line A Distance(m) 50 D 40 30 B 20 10 C A 10 20 30 Time(s) 40 50 Graphing Speed Line A: Line B: Line C: Line D: d v = = 2m/s t 20m 10s 0m = 0m/s 10s 10m = -1m/s 10s 40m = 4m/s 10s Graphing Speed D 4 3 2 A Speed(m/s) 1 B 0 10 -1 -2 Time(s) 20 30 C 40 50 Combining Velocities Velocity, like displacement, is a vector quantity. Velocity vectors can be added together to find a resultant. 500mi/hr 550mi/hr 50mi/hr 450mi/hr 50mi/hr 50mi/hr Homework 11-2 Worksheet 11-2 Due: 2/5/08 Allan Becky 20 Cindy Distance (m) 15 10 5 0 -5 -10 5 10 15 20 Time (s) Acceleration Acceleration (a, m/s²): The rate of change of velocity. Change in Speed!! Accelerate – Faster Decelerate – Slower Change in Direction Turning!! Constant Acceleration A steady change in velocity. Free Fall Free Fall The movement of an object toward Earth because of gravity. 9.8m/s2 32ft/s2 t=0s d=0m v=0m/s a=9.8m/s2 t=1s d=4.9m v=9.8m/s a=9.8m/s2 t=2s d=19.6m v=19.6m/s a=9.8m/s2 Free Fall Acceleration Acceleration (a) = change in velocity time (t) v a = t Delta “Change in” Acceleration a = v = vf - vi t t a v vf vi t – acceleration – change in velocity – final velocity – initial velocity - time Acceleration Equation vf - vi a t Acceleration vf - v i a t vf - vi a= t Time vf - v i a t vf - vi t= a Change in Velocity vf - v i a t vf – vi= at Example: A car’s velocity changes from 0 m/s to 30 m/s in 10 s. Calculate the car’s average acceleration. Given: vi = 0 m/s Find: a = ? vf = 30 m/s t = 10 s Equation : a = vf - vi t Solve : a = (30 m/s) - (0 m/s) 10 s a = 3 m/s² Graphing Acceleration Velocity (m/s) D 5 4 3 2 1 A 1 B 2 C 3 4 5 Time(s) Slope of a Velocity-Time Graph is Acceleration Accleration vs. Time 2 Accelration(m/s ) 12 10 8 9.8m.s2 6 4 2 0 1 2 3 4 Time(s) 5 6 Velocity vs. Time Velocity(m/s) 60 50 Linear Curve 40 30 20 10 0 1 2 3 4 Time(s) 5 6 Distance(m) Distanced vs. Time 140 120 100 80 60 40 20 0 Non-Linear Curve 1 2 3 4 Time(s) 5 6 Homework Worksheet 11-3 Math Practice: 1-4 Page: 346 Due: 2/12/09 Test: 2/13/09 A car traveling at 10 m/s starts to decelerate steadily. It comes to a complete stop in 20 seconds. What is its acceleration? An airplane travels down a runway for 4.0 seconds with an acceleration of 9.0 m/s2. What is its change in velocity during this time? A child drops a ball from a bridge. The ball strikes the water under the bridge 2.0 seconds later. What is the velocity of the ball when it strikes the water? A boy throws a rock straight up into the air. It reaches the highest point of its flight after 2.5 seconds. How fast was the rock going when it left the boy's hand? A car traveling at 10 m/s starts to decelerate steadily. It comes to a complete stop in 20 seconds. What is its acceleration? Homework Worksheet Word Wise - Math Due: 2/13/09 Test: 2/13/09 Connecting Motion and Forces Force (newton, N): A push or pull one body exerts on another. Earth Balanced Forces Balanced Forces: Forces on an object that are equal in size and opposite in direction. Unbalanced Forces Unbalanced Forces: Forces on an object are not equal resulting in a Net Force. 5N 3N Net Force A Net Force on an object always changes the velocity of the object. 2N Inertia Inertia (mass): The tendency of an object to resist any change in its motion. 1kg 25 kg The more mass an object has, the greater its inertia. Newton’s First Law The Law of Inertia An object moving at a constant velocity keeps moving at that velocity unless a net force acts on it. An object at rest, will remain at rest unless a net force acts on it. Friction Friction: The force opposes motion two surfaces that are touching each other. Gravity Gravity: Every object in the universe exerts a force on every other object. This force is Gravity!!! Weight Weight: The measure of the force of gravity on an object. Weight Moon (16.7 lb) Earth (100 lb) Jupiter (254 lb) Physical Science Section Wrap-up Pg: 86 Vocab: 1-10*Pg: 89 Chk Conc: 1-10* Pg:90 Due:10/5/05 * Write out questions!!!