V-t graphs and acceleration. Book page 5 8 Syllabus

Transcription

1 V-t graphs and acceleration Book page 5 8 Syllabus

2 What does the graph show?

3 Multiple-choice quiz

4 Does this show acceleration?

5 Aim Interpret velocity / time graphs to: - compare acceleration between graphs - calculate acceleration from the graph - Determine the distance travelled by the object. Demonstrate an understanding of vector quantities Use the equation: acceleration = change in velocity / time taken. Find an equation for acceleration that involves distance, time and initial velocity Key words Vector 벡터, 방향량 - Scalar Acceleration 가속도 V t graphs

6 Learning Outcomes 1. Interpret velocity / time graphs to: - compare acceleration between graphs - calculate acceleration from the graph - Determine the distance travelled by the object. 2. Demonstrate an understanding of vector quantities 3. Use the equation: acceleration = change in velocity / time taken. 4. Find an equation for acceleration that involves distance, time and initial velocity MOTION DISCOVERY LESSON Motion Graphs Use the equipment available to carry out some basic experiments. E.g Video the movement of a toy car down a ramp and then analyse its motion. Look at the WS 1 called motion graphs. Can you make the car move so as to produce a specific shape graph? Finish WS1 Make notes in your book on each type of graph and what the different shapes of line mean. Find out how pictures of velocity and acceleration look different Include a sketch for each Now that you can interpret motion graphs you need to find out how to calculate further information from the graphs. Find out: - How to calculate the acceleration from a velocity time graph - How to calculate the distance travelled from a velocity time graph. TASK You need to find out the information for yourself that will help you understand the learning outcomes. After the lessons you should be confident you understand all of these. Below I have listed different tasks you need to complete to help you understand the topic. Vector quantities. Research to find out what a vector is? What quantities in Physics are vectors? What can we say about two velocities if one of them if positive and one is negative. Homework: When completed all the worksheets, collect the HW from the teacher NEUTRALISATIO N Speed and acceleration calculations. Remember you are given the speed and acceleration equations in your exam paper but you need to be confident in using them including rearranging them. Find some information out about these acceleration equations including an example and make notes in your book. Find an equation for acceleration involving distance and time Practice using the acceleration equation by completing the sheet IGCSE Physics WS2 Use BBC bitesize and the Powerpoints on my website to help you find out the information. Include an example in your books (including drawing out the motion graph) of at least one calculation from each of the 2 bullet points above. Test your knowledge by completing worksheet 3 P2.9b. HW is also available on my website.

7 What is a scalar? Scalar quantities are measured with numbers and units. length (e.g. 16 cm) temperature (e.g. 102 C) time (e.g. 7 s)

8 What is a vector? Vector quantities are measured with numbers and units, but also have a specific direction. acceleration displacement (e.g. 30 m/s 2 upwards) (e.g. 200 miles north-west) force (e.g. 2 N downwards)

9 Speed-Time Graphs Speed (m/s) 20 Simply plots the speed of the car against the time of the journey. 10 Horizontal line means a constant speed. Sloped line means that the car is accelerating Time (s) What s going on? How can we work out the total distance travelled by the car?

10 35 Speed / Time graph for car Metres/second To calculate the distance a So the total distance is car has travelled you must = 975m calculate the area underneath the line 5 0 Time / seconds Area = ½ x 20 x 30 = 300m Area = 15 x 30 08/09/2016 cgrahamphysics.com = 450m 2016 Area = ½ x 15 x 30 = 225m

11 How is acceleration calculated? The acceleration of an object can be calculated using this equation: acceleration = change in speed time taken Change in speed is measured in metres per second (m/s). Time taken is measured in seconds (s). Acceleration is measured in metres per second per second (m/s 2 ).

12 Difference between velocity and acceleration Velocity

13 08/09/2016 Acceleration V-U Acceleration = change in velocity (in m/s) (in m/s 2 ) time taken (in s) A T 1) A cyclist accelerates from 0 to 10m/s in 5 seconds. What is her acceleration? 2) A ball is dropped and accelerates downwards at a rate of 10m/s 2 for 12 seconds. How much will the ball s velocity increase by? 3) A car accelerates from 10 to 20m/s with an acceleration of 2m/s 2. How long did this take? 4) A rocket accelerates from 1,000m/s to 5,000m/s in 2 seconds. What is its acceleration? cgrahamphysics.com m/s 2 120m/s 5s 2000m/s 2

14 08/09/2016 Acceleration V-U Acceleration = change in velocity (in m/s) (in m/s 2 ) time taken (in s) A T 1) Will accelerates from standstill to 50m/s in 25 seconds. What is his acceleration? 2) Pierre accelerates at 5m/s 2 for 5 seconds. He started at 10m/s. What is his new speed? 3) Elliott is in trouble with the police. He is driving up the A29 and sees a police car and brakes from 50m/s to a standstill. His deceleration was 10m/s 2. How long did he brake for? 4) Another boy racer brakes at the same deceleration but only for 3 seconds. What speed did he slow down to? cgrahamphysics.com m/s 2 35m/s 5s 20m/s

15 Key words 08/09/2016 cgrahamphysics.com 2016