Motion and Speed Notes 9-1 & 9-2

 An object is in motion if it changes position relative to a reference point  Stationary objects make good reference points

 Whether or not an object is in motion depends on the reference point you choose.

 Distance is the total length of the actual path between two points. Displacement is the length and direction of a straight line between starting and ending points. What is the total distance this person traveled (in blocks)? 7 Blocks What is the total displacement of this person? 5 Blocks Northeast

 Quantities that have both a magnitude and a direction  Example: Displacement

 If you know the distance an object travels in a certain amount of time, you can calculate the speed of the object.

 An airplane that moves 100 meters in two seconds has an average speed of …  Distance = 100 meters  Time = 2 seconds 100 meters = 50 meters per second 2 seconds

 The speed of most moving objects is not constant

 Rate at which object is moving at a given instant in time

 Speed in a given direction  Velocity is a vector because it has both magnitude and direction  Changes in velocity may be due to changes is speed, changes in direction, or both

 You can use distance-versus-time graphs to interpret motion.

 1 cm = 10 mm  1 m = 100 cm or 1,000 mm  1kilometer (think Sequoia 5K) – 1,000 m or 10,000 cm or 1,000,000

1.Is a moving bus a good reference point from which to measure your position? a. No, because it is often late. b. No, because it is not a stationary object. c. Yes, because it is very large. d. Yes, because it can travel very far.

1.Is a moving bus a good reference point from which to measure your position? a. No, because it is often late. b. No, because it is not a stationary object. c. Yes, because it is very large. d. Yes, because it can travel very far.

2.To describe a friend’s position with respect to you, you need to know a. Your friend’s distance from you. b. The direction your friend is facing. c. Your friend’s distance and direction from you. d. Your friend’s distance from a nearby object.

2.To describe a friend’s position with respect to you, you need to know a. Your friend’s distance from you. b. The direction your friend is facing. c. Your friend’s distance and direction from you. d. Your friend’s distance from a nearby object.

3. Two cars traveling in the same direction pass you at exactly the same time. The car that is going faster a. moves farther in the same amount of time. b. has more mass. c. has the louder engine. d. has less momentum.

3. Two cars traveling in the same direction pass you at exactly the same time. The car that is going faster a. moves farther in the same amount of time. b. has more mass. c. has the louder engine. d. has less momentum.

4. To describe an object’s motion, you need to know its a. position. b. change in position. c. distance. d. change in position over time.

4. To describe an object’s motion, you need to know its a. position. b. change in position. c. distance. d. change in position over time.

Acceleration

 Rate velocity changes with time  Vector quantity  In science, acceleration refers to increasing speed, decreasing speed, or changing direction  Decreasing speed = deceleration

 To determine the acceleration of an object, you must calculate its change in velocity per unit of time.  Acceleration = Final Velocity – Initial Velocity Time Chapter 9 Motion and Energy

 Calculate the plane’s acceleration in the first 5 seconds of motion. A= V f – V i time A = 40 m/s – 0 m/s 5 s A = 8 m/s 2

 A car traveling at 50 m/s speeds up to 80 m/s over a period of 15 seconds. The average acceleration of the car is m/s = 30 m/s = 2 m/s/s or 2m/s ² 15 s 15 s

 As a roller-coaster car starts down a slope, its velocity is 4 m/s. But 3 seconds later, its velocity is 22 m/s in the same direction. What is its acceleration?  Read and Understand  What information have you been given?  Initial velocity = 4 m/s  Final velocity = 22 m/s  Time = 3 s Chapter 9 Motion and Energy

 As a roller-coaster car starts down a slope, its velocity is 4 m/s. But 3 seconds later, its velocity is 22 m/s in the same direction. What is its acceleration?  Plan and Solve  What quantity are you trying to calculate?  The acceleration of the roller-coaster car = __  What formula contains the given quantities and the unknown quantity?  Acceleration = (Final velocity - Initial velocity)/Time  Perform the calculation.  Acceleration = (22 m/s - 4 m/s)/3 s = 18 m/s/3 s  Acceleration = 6 m/s 2  The acceleration is 6 m/s 2 down the slope. Chapter 9 Motion and Energy

 As a roller-coaster car starts down a slope, its velocity is 4 m/s. But 3 seconds later, its velocity is 22 m/s in the same direction. What is its acceleration?  Look Back and Check  Does your answer make sense?  The answer is reasonable. If the car’s velocity increases by 6 m/s each second, its velocity will be 10 m/s after 1 second, 16 m/s after 2 seconds, and 22 m/s after 3 seconds. Chapter 9 Motion and Energy

 Practice Problem  A falling raindrop accelerates from 10 m/s to 30 m/s in 2 seconds. What is the raindrop’s acceleration?  (30 m/s - 10 m/s) ÷ 2 seconds = 10 m/s 2 Chapter 9 Motion and Energy

 Practice Problem  A certain car can accelerate from rest to 27 m/s in 9 seconds. Find the car’s acceleration.  (27 m/s - 0 m/s) ÷ 9 s = 27 m/s ÷ 9 s = 3 m/s 2 Chapter 9 Motion and Energy

 You can use both a speed-versus-time graph and a distance-versus-time graph to analyze the motion of an accelerating object. Chapter 9 Motion and Energy

A student starts the 5K at 12 :15 and finishes at 12:35. What can you calculate with this information? Time: 12:35 – 12:15 = 20 min. Distance: 5K A. Speed = d/t B. Average Speed=Total distance/Total Time C. Velocity=d/t accounting for changes in speed and/or direction D. Acceleration= change in velocity/t

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 Energy of motion is kinetic energy.  Stored energy is referred to as potential energy.  The potential energy of an object depends on its weight and height.  The formula for calculating mechanical energy is  potential energy + kinetic energy = total mechanical energy