2 How do you perceive motion? Can two people look at the same object and only one of them see the object as moving?One person says that your schools is 5 blocks from the library, and another says the 2 buildings are 7 blocks apart. Can both be right?When you drop a rock off a cliff, how fast does the rock fall?Can something that is slowing down also be accelerating?We will take a look at these questions as we go through the chapter
3 11.1 Distance and Displacement To describe motion, you must state the direction and how fast the object is moving.You must also tell is location at a certain time.You also use a frame of reference if you want to describe it accurately.Frame of reference – system of objects that are not moving with respect to one anotherTennis ball**
4 Frame of Reference Relative motion – movement in relation How fast are the train passengers in the picture moving?If you are outside the train looking – they are moving quicklyIf you are on the train with them – they don’t appear to be moving.This is “frame of reference”What we are describing is relative motionRelative motion – movement in relationto a frame of reference
5 Measuring DistanceDistance – length of a path between two points (measured in meters- the SI Unit)It’s the actual path takenDisplacement – the direction from the starting pt. and the length of a straight line from the starting pt. to the ending pt.The shortest distance between 2 points
6 Combining Displacements Displacement is a vector.Vector – a quantity that has magnitude and directionMagnitude can be size, length or amount.Arrows used to represent vectors.Length of arrow shows magnitudeMagnitude is the amount or quantity of something
7 Displacement along a straight line When two displacements have the same direction, magnitudes are added.If the two displacements are in opposite directions, magnitudes are subtracted.What is the distance and displacement for A? B?
8 Displacement that’s NOT along a straight path… When 2+ displacement vectors have different directions, they may be combined be graphing.Notice the arrows (vectors) have arrows in the direction of movement and are placed tip to tailResultant vector – sum of two or more vectors (the red vector)Which is the distance and which displacement?If you take the length of the displacement vector, it equals 5 blocks while the distance walked is 7 blocks.
9 11.2 Speed and VelocitySpeed – ratio of the distance an object moves to the amount of time it movesSpeed = distance/time (SI unit)2 ways to express speed of an object are: average speed and instantaneous speedAverage speed = total distance/total time v=Instantaneous speed = measured at a particular instant (like a speedometer)dt
10 Calculating Average Speed 1 While traveling on vacation, you measure the times and distance traveled. You travel 35 kilometers in 0.4 hour, followed by 53 kilometers in 0.6 hour. What is your average speed? (v=d/t)What info are you given?Total Distance(d):Total Time(t):What are you trying to find? What formula do you need to find it?Plug it in, Plug it in!What’s the answer?
11 Calculating Average Speed 2 A person jogs 4.0 kilometers in 32 minutes, then 2.0 kilometers in 22 minutes, and finally 1 km in 16 minutes. What is the jogger’s average speed in kilometers per minute?(v=d/t)What info are you given?Total Distance(d):Total Time(t):What are you trying to find? What formula do you need to find it?Plug it in, Plug it in!What’s the answer?
12 Calculating Average Speed 3 A train travels 190 km in 3 hours, and then 120 kilometers in 2 hours. What is its average speed?(v=d/t)What info are you given?Total Distance(d):Total Time(t):What are you trying to find? What formula do you need to find it?Plug it in, Plug it in!What’s the answer?
13 Graphing Motion Distance-time graph Slope of a d-t graph shows speed Slope is change in y (vertical) divided by change in x (horizontal)Steeper line = faster speedStraight line shows constant speed
14 Velocity V= 17 km/h The resultant velocity is 13 km/h Velocity is speed in a given direction.Velocity is a vectorCalculated the same way as speed. V=d/tVelocities can be combined with vector additionV= 17 km/hThe resultant velocity is 13 km/h
15 11.3 AccelerationWe often think of acceleration when the speed of an object is increasing. However, acceleration results from increases OR decreases in speed.Acceleration – the rate at which velocity changesCan be change in speed OR directionAcceleration is speeding up, slowing down, starting, stopping, or changing direction.Acceleration is a vector.Accel. = final velocity – initial velocity/timea = Vf –Vi / t
16 Free Fall t = 0 s v = 0 m/s t = 1 s v = 9.8 m/s t = 2 s v = 19.6 m/s Free fall – movement of an object toward Earth because of gravityObjects in free fall accelerateAcceleration due to gravity near earth’s surface is a constant, g = 9.8 m/s2Imagine the stone in figure 12 falling from the mouth of the well.After 1S the stone will be falling at 9.8m/sAfter 2S the stone will be going faster by +9.8 to 19.6, then after 3 s, another 9.8 to 29.4t = 2 s v = 19.6 m/st = 3 s v = 29.4 m/s
17 Acceleration Acceleration isn’t always the result of changes in speed. You can accelerate even if your speed is constantRiding a bike around a curve – you have a constant speed, but your change in direction means you are acceleratingSometimes you have change in speed and direction at the same timeA roller coaster ride starts out slowly as the cars travel up, they reach the top and plummet down. You are thrown around as your acceleration changes constantly.
18 Constant Acceleration Constant Acceleration – steady change in velocityThe velocity changes by the same amount each secondEx: constant acceleration during takeoff results in changes in an aircraft’s velocity that are in a constant directionYou calculate acceleration for straight-line motion by dividing the change in velocity by the total timeAcceleration = change in velocity = (Vf-Vi)total time tDo Math Skills on pg
19 Speed-Time Graphs Graphs of Accelerated Motion Linear graphs display dataSpeed-time graphSlope shows accelerationStraight line shows constant accelerationSteeper slope shows greater increase or decrease per unit time
20 Speed vs. TimeIncrease in speed is positive acceleration.
21 Speed vs timeDecrease in speed is negative acceleration.
22 Distance-Time Graphs Nonlinear graph A distance-time graph of accelerated motion is a curveIncreasing slope on a d-t graph means speed is increasing.Instantaneous Acceleration – how fast velocity is changing at a specific instantNonlinear graph
23 Can we answer the questions? Can two people look at the same object and only one of them see the object as moving?One person says that your schools is 5 blocks from the library, and another says the 2 buildings are 7 blocks apart. Can both be right?When you drop a rock off a cliff, how fast does the rock fall?Can something that is slowing down also be accelerating?