# Observe, describe, and compare the motion of objects using speed. Describe and calculate acceleration using change in the speed over time. WARM-UP Student.

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Observe, describe, and compare the motion of objects using speed. Describe and calculate acceleration using change in the speed over time. WARM-UP Student Objective What does a straight steep line pointing up mean on a speed graph?

2 http://www.bbc.co.uk/schools/gcsebitesize/scienc e/add_ocr_gateway/forces/changingspeedact.sht ml BBC Bitesize http://www.pbslearningmedia.org/resource/phy03.s ci.phys.mfw.accel/virtual-car-velocity-and- acceleration/

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A B C D Look at the graph below: Which line shows an object that is moving”? _____ Which line shows a fast, steady speed? ______ Which line shows no movement? ______ Which line shows a slow, but steady speed? _________

6 Which line shows a constant speed? _____ Which lines show acceleration? ______and _____ Which lines shows deceleration? ______ A D B C SPEEDSPEED Interpreting Acceleration Graphs The steeper the line, the greater the acceleration. A horizontal line means the object is moving at a steady speed. A downward sloping line means the object is slowing down or “decelerating”.

7 Practice Worksheet Interpreting Speed & Acceleration worksheet Match the Graph http://www.physicsclassroom.com/Physics- Interactives/1-D-Kinematics/Graphs-and- Ramps/Graphs-and-Ramps-Interactive Science of football… https://www.nbclearn.com/nfl/cuecard/50770

8 Calculating Acceleration As a roller-coaster car starts down a slope, its speed is 4 m/s. But 3 seconds later, at the bottom, its speed is 22 m/s. What is its average acceleration? Read and Understand What information have you been given? Initial speed = 4 m/s Final Speed = 22 m/s Time = 3 s

9 Calculating Acceleration As a roller-coaster car starts down a slope, its speed is 4 m/s. But 3 seconds later, at the bottom, its speed is 22 m/s. What is its average acceleration? Plan and Solve What quantity are you trying to calculate? The average acceleration of the roller-coaster car = __ What formula contains the given quantities and the unknown quantity? Acceleration = (Final speed – Initial speed) ÷ Time Perform the calculation. Acceleration = (22 m/s – 4 m/s)/3 s = m/s/3 s Acceleration = m/s 2 The roller-coaster car’s average acceleration is m/s 2. 18 6 6

10 Calculating Acceleration As a roller-coaster car starts down a slope, its speed is 4 m/s. But 3 seconds later, at the bottom, its speed is 22 m/s. What is its average acceleration? Look Back and Check Does your answer make sense? The answer is reasonable. If the car’s speed increases by 6 m/s each second, its speed will be 10 m/s after 1 second, 16 m/s after 2 seconds, and 22 m/s after 3 seconds.

11 - Acceleration To determine the acceleration of an object moving in a straight line, you must calculate the change in speed per unit of time. Acceleration = (24m/s -0m/s) ÷ 3 m/s = 8 m/s 2

12 Calculating Acceleration A falling raindrop accelerates from 10 m/s to 30 m/s in 2 seconds. What is the raindrop’s average acceleration? A certain car can accelerate from rest to 2.7 m/s in 9 seconds. Find the car’s average acceleration.

13 Calculating Acceleration Practice Problem A falling raindrop accelerates from 10 m/s to 30 m/s in 2 seconds. What is the raindrop’s average acceleration? (30 m/s – 10 m/s) ÷ 2 seconds = 10 m/s 2

14 Calculating Acceleration A certain car can accelerate from rest to 2.7 m/s in 9 seconds. Find the car’s average acceleration. (2.7 m/s – 0 m/s) ÷ 9 s = 2.7 m/s ÷ 9 s = 0.3 m/s 2

15 Motion Interactives Graph That Motion – Challenging!Graph That Motion Click on the following link to watch a movie about speed, velocity and acceleration and to take an online quiz! Video and Quiz

16 Homework Worksheet Graphing Notes: Interpreting Speed Graphs

17 Conclusion Answer the following questions: If you know an object’s speed and the time they have traveled then you can calculate the _____________. If you know an objects speed and the direction it is travelling in then you know the object’s ____________. Three ways an object can accelerate are _______, _______ and _______. 17

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