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Motion

Motion. GCSE Physics. Learning Intentions. By the end of the lesson we will be able to… State the difference between displacement and distance Recall the equation for calculating speed and apply it to solve simple problems State the difference between speed and velocity.

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Motion

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  1. Motion GCSE Physics

  2. Learning Intentions • By the end of the lesson we will be able to… • State the difference between displacement and distance • Recall the equation for calculating speed and apply it to solve simple problems • State the difference between speed and velocity

  3. By definition… • Distance (…travelled)- the total length of journey taken from start to finish (metre) • Displacement- a measure of the overall change of position, including the direction (metre with direction) Finish Start 2m 2m N 4m Eg. Distance travelled is 8 metres Displacement is 4 metres, east

  4. Coleraine 8 miles Questions Ballymoney Ballymena • A man drives from Ballymena to Coleraine. The 2 towns are 22 miles apart. • What is the distance travelled? • What is his displacement? • What is his displacement if he turns around at Coleraine and stops at Ballymoney? • a) 22 miles b) 22 miles N c) 14 miles N

  5. Displacement • Extra wee bit The displacement of an object after a journey can be zero- The total distance travelled was 50 metres 25m Journey A – B and then B - A A B 10m A B Total displacement from A to B and B back to A… zero

  6. Ferrari 360 Spider Speed The rate at which an object changes the distance it has travelled is called its speed. For a complete journey the speed of an object can be calculated by dividing the total distance covered by the time taken to complete the journey- Average Speed = Total Distance / Time Taken metres/second = metre / second distance speed time

  7. Lance Armstrong Velocity • This is the quantity given to the displacement travelled in unit time in a given direction OR • The rate of change of displacement • Velocity is a vector quantity e.g. the bike’s velocity is 24 m/s East Size direction

  8. Scalar versus Vector • Scalars are quantities which are only described by their size • Vectors are quantities which require both a size and a direction.

  9. Question Time • Page 69 • Questions 1-4 1 mile = 1600 m

  10. Learning Intentions • By the end of the lesson we will be able to… • Recall the equation for calculating acceleration and apply it to solve simple problems • Recognise acceleration as a vector quantity

  11. Acceleration • Which object has the greatest Acceleration?

  12. Snap Shots • Constant Velocity • Changing Velocity Disp Disp.

  13. Acceleration Equation • The average acceleration of an object is given by the change in velocity per unit time- Acceleration = Change in Velocity / Time Taken Acceleration = (Final Velocity – Initial Velocity) / Time Taken a = (v – u) / t m/s2 = m/s / s Δv a t

  14. Usain Bolt’s Acceleration • Work out Usain’s change in motion during • first 30 metres • last 20 metres

  15. Wee bit extra • Acceleration is a vector quantity. It can be a positive or negative value. When an object’s initial velocity is greater than the final velocity then it is said to be slowing down or decelerating (negative acceleration)

  16. Examples • Example A • Acceleration = change in velocity / time taken = (8 – 0) / 4 = 8 / 4 = 2 m/s2 • Example B • a = Δv / t = (0 – (-8)) / 4 = 8 / 4 = 2 m/s2

  17. Complete the Chart showing steady acceleration • All Velocities are in m/s • Calculate the accelerations of X and Y • What is special about the acceleration of X? Explain it’s journey… 8.0 4.0 10.0 5.0 X = 2 m/s2 Y = -2.5 m/s2

  18. Homework Questions • Page 70, Qs 5 - 8

  19. Vectors and Scalars • Spot the vectors among thescalars 67 m/s 94 Joules 12 seconds 5 m/s - 17 m/s2 16 Newtons 7 N 16 m due North Weight

  20. Learning Intentions • By the end of the lesson we will be able to… • Construct a distance-time graph to represent motion • Identify common shapes of a d-t graph • Use a d-t graph to calculate an unknown speed

  21. Distance – Time Graphs • This is a visual way of representing motion by using a graph.

  22. Distance- Time Graphs Dist. Distance (m) Straight line, positive correlation, both increase at the same rate

  23. Distance- Time Graphs Dist. Distance (m) Curves up, as seconds pass, the car covers more distance than the second before

  24. Graphs of motion • Distance -Time graph (Pg 71) Some of the common shapes that describe the motion of an object are- speed speed speed Increasing speed Decreasing speed

  25. Question time... • Page 73 in CCEA • Question 10 (answer in full!)

  26. Learning Intentions • By the end of the lesson we will be able to… • Identify common shapes of a d-t graph • Use a d-t graph to calculate an unknown speed • Recognise the link between the gradient of a d-t graph for an object and the motion of that object

  27. Gradient • The word ‘gradient’ is used to explain the shape of the line on the graph 3 1 2 4 5 • Match the phrases to the correct graphs

  28. Gradient • A value for the gradient of a graph can be calculated by dividing the change in the ‘y value’ by the change in the ‘x value’ 75 4.8 y y 0 0 15 1.2 x x Gradient = -4.8 / 1.2 = -4 Gradient = 75 / 15 = 5 Negative gradient, slope down

  29. The change in y is the distance the object has travelled The change in x is the time the object was travelling Speed equals distance divided by time, therefore the gradient of the graph is thesameas the speed of the object

  30. What is the gradient, and hence the speed of the car? Change in y = Distance travelled = 800 – 200 = 600 m Change in x = Time taken = 36 - 16 = 20 s Gradient = Speed = Distance / Time = 600 / 20 = 30 m/s

  31. Learning Intentions • By the end of the lesson we will be able to… • Identify common shapes of a v-t graph • Use a v-t graph to calculate an unknown acceleration • Recognise the link between the gradient of a v-t graph for an object and the motion of that object

  32. Graphs of motion • We’ve seen how Distance-Time graphs can be a clear illustration of an object’s motion. Another usefully way to present this motion is in the form of a Velocity- Time graph.

  33. Felix is bonkers…

  34. Graphs of motion • Velocity -Time graph Some of the common shapes that describe the motion of an object are- v v v t t Slower constant speed Acceleration Constant speed speed speed speed v v v t Deceleration t Increasing speed Decreasing speed Stopped Slower Acceleration

  35. Gradient Summary • For a Distance-Time Graph the gradient at any instant represents the speed - eg. Zero (flat) gradient means no speed • For a Velocity-Time Graph, the gradient at any instant represents the acceleration - eg. Steep (high) gradient means large acceleration

  36. Learning Intentions • By the end of the lesson we will be able to… • Calculate displacement from a v-t graph • Recall what is meant by an object’s momentum • State the equation for momentum and solve simple problems related to momentum

  37. Wee Bit Extra Consider this example- A car travels at 4 m/s for 10 s • Velocity / Time graph for the motion 4 Velocity (m/s) 10 Time (s)

  38. 4 Velocity (m/s) Area under the graph!! 10 Time (s) Velocity = Displacement / Time From the graph- Velocity = 4 m/s Time = 10 s Re-arrange the equation- d = v x t = 4 x 10 = 40 m d v t

  39. Displacement • For a Velocity-Time graph the displacement can be calculated by finding the area under the line

  40. Examples • What is the total displacement of each of the object’s motion illustrated in the graphs below- V V 15 5 t t 8 16 200 Area under line = (5 x 8) + (0.5 x 8 x 5) Displacement = 60 m Area under line = 15 x 200 Displacement = 3000 m

  41. Try this one… • Pg 74 • Questions 13 (Ignore the last sentence in Q13 about the ‘graphical method’)

  42. Momentum • The Superhero factor! verses

  43. Momentum • If an object is moving then it has momentum. This can be calculated by using the equation- Momentum = Mass x Velocity p = m x v kgm/s = kg x m/s Momentum is a vector quantity

  44. Example • What is the momentum of i) the car, ii) the motorcycle? • Which would have more momentum if they were both travelling at the same velocity, why?

  45. Momentum = mass x velocity p = m x v - For the car p = 1000 x 5 = 5000 kgm/s - For the motorcycle p = 200 x 30 = 6000 kgm/s • If they were both travelling at the same speed the car would have the most momentum as it has the most mass

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