Warm Up February 3, 2016 Speed-Time Graphs Motion and Acceleration Velocity Velocity the SPEED and DIRECTION of an object. Example: An airplane moving North at 500 mph A missile moving towards you at 200 m/s Acceleration Acceleration the rate at which velocity changes Can be an: Increase in speed Decrease in speed Change in direction Types of Acceleration Increasing speed Example: Car speeds up at green light Decreasing speed Example: Car slows down at stop light Changing Direction Example: Car takes turn (can be at constant speed) screeeeech Question How can a car be accelerating if its speed is a constant 65 km/h? Answer: If it is changing directions it is accelerating. Calculating Acceleration If an object is moving in a straight line Units of acceleration: m/s 2 Graphing Acceleration Can use 2 kinds of graphs to show acceleration. Speed vs. time Distance vs. time Constant Speed in a Speed vs. Time Graph Speed does not change over time, therefore speed is constant. Speed is 8 m/s. Acceleration in a Speed vs. Time Graph Speed is increasing with time, therefore it is accelerating. The straight line indicates that acceleration is constant. Acceleration in a Speed vs. Time Graph Speed is decreasing with time, therefore it is accelerating (deceleration). No Speed in a Speed vs. Time Graph Speed stays at 0 m/s over time. The object is stationary (standing still). Graphing Acceleration: Speed vs. Time Graphs In Speed vs. Time graphs: Acceleration = Rise/Run = 4 m/s 2 s = 2 m/s 2 Above is a graph showing the speed of a car over time. 1) How is the speed of the car changing? (speeding up, slowing down, or staying the same) 2) What is this cars acceleration? Answer: Acceleration = rise/run = -6m/s 3s = -2 m/s 2 Answer: The car is slowing down REVIEW QUESTIONS Which of the following words describes a speed and a direction? A) Speed B) Acceleration C) Velocity D) Displacement Answer: Velocity = speed and a direction (Ex: 50 mph northeast) REVIEW QUESTIONS Which of the following words describes when velocity changes? A) Speed B) Acceleration C) Velocity D) Displacement Answer: Answer = acceleration occurs whenever velocity changes. REVIEW QUESTIONS Which of the following are examples of velocity changing? A) Going a constant speed of 50 mph. B) Going a constant speed of 50 mph and curving to the left. C) Decreasing speed to 30 mph. D) Increasing speed to 60 mph. Answer: Answer = acceleration occurs whenever velocity changes, since velocity is a speed and a direction, the answer is B,C,D. RQ: In this D/T graph, which lines show acceleration? 1)Which line represents an object that is accelerating? The black (D) and red (A) lines represent a objects that are accelerating. Black is going a greater distance each second, so it must be speeding up. Red is going less each second, so must be slowing down Remember: in distance vs. time graphs: curved line = accelerating, flat line = constant speed REVIEW QUESTIONS Draw an example of constant speed on a Distance-Time graph. REVIEW QUESTIONS Draw an example of constant speed on a Speed-Time graph. REVIEW QUESTIONS Draw an example of acceleration (INCREASING speed) on a Distance-Time graph. REVIEW QUESTIONS Draw an example of acceleration (INCREASING speed) on a Speed-Time graph. REVIEW QUESTIONS Draw an example of acceleration (DECREASING speed) on a Distance-Time graph. REVIEW QUESTIONS Draw an example of acceleration (DECREASING speed) on a Speed-Time graph. REVIEW QUESTIONS Draw an example of a stationary object on a distance-time graph. REVIEW QUESTIONS Draw an example of a stationary object on a speed-time graph.