DESCRIBING MOTION Chapter 1 Material on Final Exam

Chapter 1 • Last Scientist Standing! True False Displacement is the distance an object moves along a path Constant speed is the same thing as average speed Physics will have more math than chemistry Velocity is another name for speed An object accelerates when either its speed or direction changes The description of an object’s position depends on a reference point 2

Chapter 1 • Essential Questions: • How does the description of an object’s position depend on a • • reference point? How can you describe the position of an object in two dimensions? What is the difference between distance and displacement? What is speed? How can you use a distance-time-graph to calculate average speed? What are ways velocity can change? What are three ways an object can accelerate? What does a speed-time graph indicate about an object’s motion? 3

Section 1: Position and motion • A reference point is the starting point you choose to describe the location, or position, or an object distance • The position of an object is its ______ direction and ______ from a reference point nce e r e f e Our r s THE i __ point __T _ H _ ___R ____EAually) (us 4

Section 1: Position and motion Motion • _______ is the process of changing position • When we see things move, it is based on a reference point _________ 5

Section 1: Position and motion • Distance and Displacement path • Distance depends on the _______ taken • Displacement is the difference between the initial (first) position and the final position of the object shortest • Always the ______ path! Line Distance Displacement A B C D 6

Section 2: Speed and Velocity • What is speed? Speed • _____ is a measure of the distance an object travels per unit of time m/s • SI unit is _____ • Other units: mi/h, km/h, ft/s 7

Section 2: Speed and Velocity • Constant Speed • Rate of change of position in which the same ____ distance is traveled each second. • Instantaneous Speed specific • Speed at a _____ instant in time = distance time 8

Section 2: Speed and Velocity • Average Speed • _______ distance traveled divided by the ____ Total time taken to travel that distance = total distance total time 9

Section 2: Speed and Velocity 1. Write the formula What is the average speed for the whole trip? 2. Identify variables 3. Plug in numbers 4. Solve and circle 10

Section 2: Speed and Velocity 1. Write the formula A snail moves 1 m in 100 seconds. What is the speed ? 2. Identify variables 3. Plug in numbers 4. Solve and circle 11

Section 2: Speed and Velocity 1. Write the formula 2. Identify variables A car is driving along at 25 km/hr. How long will it take me to drive 400 km? 3. Plug in numbers 4. Solve and circle 12

Section 2: Speed and Velocity 1. Write the formula 2. Identify variables A bee is flying by at a speed of. 75 m/s. How far will the bee travel in 60 seconds? 3. Plug in numbers 4. Solve and circle 13

Section 2: Speed and Velocity Distance-Time graphs • This type of graph is based on the most basic things we need to know about the motion of an object (_______ and distance time _____). X • Time goes on the ___ axis Y • Position / Distance goes on the ___-axis away • IF the object moves _____ from start, we increase _________ distance (+) toward • IF the object moves ______ start, we decrease ______ distance (-) • Draw each section a bit at a time • No best fit lines! 14

Section 2: Speed and Velocity • Elements of a Distance-Time Graph • Slowing down- ________ (-) slope Decreasing • Stopping- ____ slope (horizontal line) No • Speeding up- ________ (+) slope Increasing • Average speed- Find the distance changed and the time changed between a starting point and a stopping point. 15

Section 2: Speed and Velocity Dance Class Movement 100 90 Distance from wall (feet) 80 70 60 50 40 30 20 10 0 0 15 30 45 60 75 Time (seconds) 90 105 120 135 150 16

Section 2: Speed and Velocity • What is happening from 0 -30 seconds? • What is happening from 0 -60 seconds? • From 60 -75 seconds? • From 75 -90 seconds? • From 90 -105 seconds? • 105 to 120? • 120 to 135? • 135 to 150? 17

Section 2: Speed and Velocity • What is the speed of the dancer from… • 30 to 60 seconds? • 90 to 105 seconds? • 135 to 150 seconds? 18

Section 2: Speed and Velocity Speed ≠ Velocity • _______ is the speed of an object in a Velocity given direction • Velocity MUST include a ______! 19

Section 2: Speed and Velocity • Which is it? Speed or Velocity? • 7 miles per hour • 2. 345 inches/minute east • 18. 7 ft/s down • 7. 77 km/day 20

Section 2: Speed and Velocity • Changes in Velocity speed • Could be a change in the actual ____ direction • Could be a change in _______ both • Could be _____! 21

Section 2: Speed and Velocity • Combining Velocities • When you combine velocities together, you have to look at the direction ADD • If they are in the same direction, you ______ them • If they are in different directions, you _______ SUBTRACT THEM • ***MAKE SURE TO INCLUDE THE DIRECTION*** 22

Section 2: Speed and Velocity • Combining velocities • I walk 3 ft/s down while the escalator pushes me 5 ft/s up. What is the resultant velocity? • A bird is flying at a velocity of 5 km/hr west when a gust of wind pushes her with a velocity of 10 km/hr west. What is the resultant velocity? 23

Section 3: Acceleration • Acceleration not • Does ____ always mean “speed up”! Acceleration • __________ is a measure of the change in velocity during a period of time 24

Section 3: Acceleration • Calculating Average Acceleration • Units for acceleration: _____ m/s 2 25

Section 3: Acceleration • Math Practice • Use the equation for average acceleration to do the following problem. • A plane passes over point A at a velocity of 240 m/s north. Forty seconds later, it passes over point B at a velocity of 260 m/s north. What is the plane’s average acceleration? • Write the formula • Show your work • Solve with correct number • Include correct units 26

Section 3: Acceleration • Math Practice—Solving for Acceleration (a) • A roller coaster’s velocity at the top of the hill is 10 m/s. Two seconds later it reaches the bottom of the hill with a velocity of 26 m/s. What is the acceleration of the coaster? 27

Section 3: Acceleration • Math Practice—Solving for time (t) • How long will it take a car to go from 0 to 45 km/hr if they are accelerating at 5 km/hr 2? 28

Section 3: Acceleration • Math Practice—Solving for starting/initial velocity (vi) • You roll a bowling ball for 4 s. The ball traveled at a constant acceleration of 2 m/s 2 down the lane and was traveling at a speed of 9 m/s by the time it reached the pins at the end of the lane. How fast was the ball going when it left Tim’s hand? 29

Section 3: Acceleration • Math Practice—Solving for final velocity (vf) • If a truck, with an initial velocity of 10 m/s, accelerates at a rate of 30 m/s 2 for 3 seconds, what will its final velocity be? 30

Section 3: Acceleration 31

Section 3: Acceleration • Recognizing Acceleration on a Graph • Velocity has to CHANGE over time 32

Section 3: Acceleration • Speed-Time graphs time • X-axis is the same (____) Velocity (m/s) • Y-axis is now ______ • Elements of a speed-time graph • Object at rest- horizontal line where _______ Y=0 • Constant speed- _______ line horizontal positive • Speeding up- _____ (+) slope • Slowing down- ______ (-) slope negative 33