CHAPTER 9 ENERGY AND MOTION Section 1 Describing

CHAPTER 9 ENERGY AND MOTION

Section 1: Describing Motion When is an object in motion? What is the difference between distance and displacement?

I. Motion- distance from another object is changing A. B. C. D. E. Reference point- object used for comparison to determine motion 1. Best = Stationary- not moving pair of opposing directions a. 3 seats in front = +3, 5 rows back = -5 Relative motion- Whether or not an object is in motion depends on the reference point you choose. 1. Reading book- chair = ref pt = not moving 2. Reading book - sun = ref pt = moving Distance- length of a path between 2 points Displacement- length and direction that an obj moved from starting point Vector- both magnitude and direction 1. uses arrows

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

Chapter 9 Motion and Energy Distance and Displacement o 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.

Chapter 9 Motion and Energy End of Section: Describing Motion

Chapter 9 Motion and Energy Section 2: Speed and Velocity

I. Speed and Velocity A. Calculate Speed (rate) 1. Speed (rate) = distance/time 2. R= d/t or D=rt or t= r/d B. Average speed 1. Speed on trip usually not constant 2. Total distance/total time C. Instantaneous speed- rate at a specific instant

Chapter 9 Motion and Energy Calculating Speed o If you know the distance an object travels in a certain amount of time, you can calculate the speed of the object.

II. Velocity - speed AND direction A. Vector- shown by length and direction of an arrow B. Change in velocity = change in speed, direction or both

III. Graphing Speed A. Distance vs. time graphs = linear equation 1. 2. 3. 4. Slope = speed Positive correlation X = time, y = distance Usually not at constant speed- shows on graph

Graphing Motion o You can use distance-versus-time graphs to interpret motion.

Chapter 9 Motion and Energy Graphing Motion Activity

Chapter 9 Motion and Energy Velocity o Click the Video button to watch a movie about velocity.

Chapter 9 Motion and Energy End of Section 2: Speed and Velocity

Section 3: Acceleration What kind of motion does acceleration refer to? How do you calculate acceleration? What graphs can be used to analyze the motion of an accelerating object?

I. Changing velocity A. Acceleration- rate velocity changes 1. Increase or decrease in speed 2. Change in direction B. Calculate acceleration = final v – initial v/ time C. Graphing acceleration 1. Speed v time a. Straight line = accelerating at constant rate b. m/s(2) 2. Distance v time a. m/s b. Curved line = increasing speed

Calculating Acceleration-To determine the acceleration of an object, you must calculate its change in velocity per unit of time. (fv)40 m/s – (iv) 0 m/s / 5 s (time) = 8 m/s 2

Chapter 9 Motion and Energy Calculating Acceleration 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? What information have you been given? o Initial velocity = 4 m/s o Final velocity = 22 m/s o Time = 3 s

Chapter 9 Motion and Energy Calculating Acceleration What quantity are you trying to calculate? o The acceleration of the roller-coaster car = __ What formula contains the given quantities and the unknown quantity? o Acceleration = (Final velocity - Initial velocity)/Time Perform the calculation. o Acceleration = (22 m/s - 4 m/s)/3 s = 18 m/s/3 Acceleration = 6 m/s 2

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

Chapter 9 Motion and Energy Graphing Acceleration o 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 Links on Acceleration o Click the Sci. Links button for links on acceleration.

Chapter 9 Motion and Energy End of Section: Acceleration

Section 4: Energy What factors affect an object’s kinetic energy and potential energy? How can kinetic energy and potential energy be transformed? What is the law of conservation of energy?

I. Kinetic Energy- energy an object has due to motion A. Depends on both its mass (g) and speed (m/s) B. ½ x mass x speed (2) g x m/s (2) C. Spinning, vibrating, moving from one point to another

Chapter 9 Motion and Energy Exponents o An exponent tells how many times a number is used as a factor. For example, 3 x 3 can be written as 32. You read this number as “three squared. ” In the formula for kinetic energy, speed is squared. For example, you can calculate the kinetic energy of a 70 -kg person moving at a speed of 2 m/s by using the formula below. KE = ½ x Mass x Speed 2 = ½ x 70 kg x (2 m/s) 2 = 140 kg • m 2/s 2 or 140 joules. Note: 1 kg • m 2/s 2 = 1 joule

Chapter 9 Motion and Energy Exponents o Practice Problem What is the kinetic energy of a 30 -kg rock moving at a speed of 10 m/s? 1, 500 joules

Chapter 9 Motion and Energy Kinetic Energy o Kinetic energy increases as mass and speed increase.

II. Potential Energy- stored energy that results from the position or shape of an object A. Gravitational- weight and height relative to ref point 1. Gpe = weight x height 2. Ex. = skier at top of hill weighs 500 n and jump is 40 m, 500 x 40 = 20, 000 J of gpe B. Elastic- stretched or compressed A. Ex- bow pulled, spring squeezed

Potential Energy o Gravitational potential energy increases as weight and height increase.

III. Energy transformation and conservation A. Mechanical energy- combined kinetic and potential (me = ke + pe) B. Most common transf = potential to kinectic A. Ex. Waterfall- top = pe, once spills over edge = ke (gravitational) C. Conservation- transformation doesn’t destroy energy (ke changes into thermal energy, ect. )

Transformations Between Potential and Kinetic Energy o A pendulum continuously transforms energy from kinetic to potential energy and back.

Chapter 9 Motion and Energy Transformations Activity o Click the Active Art button to open a browser window and access Active Art about energy transformations.

Chapter 9 Motion and Energy Links on Energy o Click the Sci. Links button for links on energy.

Chapter 9 Motion and Energy Links on Forms of Energy o Click the Sci. Links button for links on forms of energy.

End of Section: Energy