2 Acceleration Acceleration = speeding up Acceleration – the rate at which velocity changesCan be an:Increase in speedDecrease in speedChange in direction
3 Types of acceleration Increasing speed Decreasing speed Example: Car speeds up at green lightDecreasing speedExample: Car slows down at stop lightChanging DirectionExample: Car takes turn (can be at constant speed)screeeeech
4 QuestionHow can a car be accelerating if its speed is a constant 65 km/h?If it is changing directions it is accelerating
5 Calculating Acceleration If an object is moving in a straight lineUnits of acceleration:Distance/ time = distance/time2timem/s2
7 QuestionA skydiver accelerates from 20 m/s to 40 m/s in 2 seconds. What is the skydiver’s average acceleration?
8 Graphing Acceleration Can use 2 kinds of graphsSpeed vs. timePosition vs. time
9 Graphing Acceleration: Speed vs. Time Graphs Speed is increasing with time = acceleratingLine is straight = acceleration is constant
10 Graphing Acceleration: Speed vs. Time Graphs Rise = 4 m/sRun = 2 sIn Speed vs. Time graphs:Acceleration = Rise/Run= 4 m/s ÷ 2 s = 2 m/s2
11 Graphing Acceleration: Position vs. Time Graphs On Position vs. Time graphs a curved line means the object is accelerating.Curved line also means your speed is increasing. Remember slope = speed.
12 Question Run = 3 s Rise = -6 m/s 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 car’s acceleration?The car is slowing downAcceleration = rise/run = -6m/s ÷3s = -2 m/s2
13 curved line = accelerating, straight line = constant speed Question:The black and red 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 downRemember: in position vs. time graphs:curved line = accelerating,straight line = constant speedWhich line represents an object that is accelerating?
15 Free fallThe constant acceleration of an object moving only under the force of gravityIf there was no air, all objects would fall at the same speed regardless of the masses
16 Acceleration due to gravitational force d = vit + ½gt2If vi = 0, then d = ½ gt2g = acceleration due to the force of gravity= 9.8 m/s2= 10 m/s2
17 Free fall After 1 second falling: v= 10 m/s After 2 seconds: v = 20 m/sAfter 3 seconds: v = 30 m/s
18 Falling Air resistance will increase as it falls faster An upward force on the objectEventually gravity will balance with air resistanceReaches terminal velocity - highest speed reached by a falling object.
20 QuestionsAnswer the following questions and me your answers. )1. How can a car accelerate without the speedometer changing?2. What does the slope of a velocity vs time graph give you?3. What is the value of the acceleration due to the force of gravity on Earth?4. What is the color of the object that is rolled across the table by Mr. Andersen?