abp_kinematicspresentation for 1819.notebook September 13, 2018 2 A - PDF document

abp_kinematics­presentation for 1819.notebook September 13, 2018 Distance We'll be using meter as our standard for measuring distance. The symbol for distance is "d". And the unit for the meter is "m" Algebra Based Physics Kinematics d = 0.2 m www.njctl.org www.njctl.org Aug 14­2:24 PM Speed Time We will be using the second as our standard for measuring time. Speed is defined as the distance traveled divided by the The symbol for time is "t" time it took to travel that distance. The unit for a second is "s". t = 10s Demo speed = distance time Speed is not a fundamental aspect of nature, it is the ratio of two things that are. Click here a "minute physics" video on measuring time and distance Aug 14­2:24 PM Aug 14­2:24 PM Speed The units of speed can be seen by substituting the units for 1 A car travels at a constant speed of 10m/s. This distance and time into the equation means the car: A increases its speed by 10m every second. B decreases its speed by 10m every second. meters seconds Answer C moves with an acceleration of 10 meters every second. D moves 10 meters every second. We read this unit as "meters per second" E I need help https://www.njctl.org/video/?v=7E8c3jVbN2w Aug 14­2:24 PM May 9­8:46 PM 1

abp_kinematics­presentation for 1819.notebook September 13, 2018 2 A rabbit runs a distance of 60 meters in 20 s; 3 An airplane on a runway can cover 500 m in 10 s; what is the speed of the rabbit? what is the airplane's average speed? A 0.3 m/s A 0.02 m/s B 0.6 m/s B 50 m/s Answer Answer C 3 m/s C 100 m/s D 4 m/s D 5000 m/s E I need help E I need help https://www.njctl.org/video/?v=XrtRbPudROU https://www.njctl.org/video/?v=OJNi1GsWnuI Aug 14­2:24 PM Aug 14­2:24 PM 4 A car travels at a speed of 40 m/s for 4.0 s; 5 You travel at a speed of 20m/s for 6.0s; what what is the distance traveled by the car? distance have you moved? A 4 m A 6 m B 10 m B 20 m Answer Answer C 160 m C 120 m D 320 m D 160 m E I need help E I need help https://www.njctl.org/video/?v=mPMcjq1CNxA https://www.njctl.org/video/?v=CWvo93CQnNI Aug 14­2:24 PM Aug 14­2:24 PM 7 You travel at a constant speed of 30m/s; how much time does it take you to travel a distance of 150m? 6 You travel at a constant speed of 20 m/s; how much time does it take you to travel a distance of 120m? A 0.2 s B 5 s A 6 s Answer C 15 s B 12 s Answer D 30 s C 20 s E I need help D 60 s E I need help https://www.njctl.org/video/?v=k7od93faZ3E https://www.njctl.org/video/?v=_8JNZyQXze4 Aug 14­2:24 PM Aug 14­2:24 PM 2

abp_kinematics­presentation for 1819.notebook September 13, 2018 Average Speed The speed we have been calculating is a constant speed over Average Speed a short period of time. Another name for this is instantaneous speed. Demo If a trip has multiple parts, each part must be treated separately. In this case, we can calculate the average speed for a total trip. Determine the average speed by finding the total distance you traveled and dividing that by the total time it took you to travel that distance. Return to Table of Contents https://www.njctl.org/video/?v=Ry­IJYdAYhk Jun 29­2:17 PM Sep 8­4:20 PM Distance and Time Intervals Average Speed & Non­Uniform Motion The following pattern of steps will help us to find the average In physics we use subscripts in order to avoid any confusion speed: with different distances and time intervals. Find the total distance d total = d 1 + d 2 + d 3 For example: if an object makes a multiple trip that has three parts we present them as d 1 , d 2 , d 3 and the corresponding time Find the total time t total = t 1 + t 2 + t 3 intervals t 1 , t 2 , t 3 . Use the average speed formula s avg = d total t total Jul 13­10:15 AM Jul 13­10:15 AM Average Speed ­ Example 1 It takes Sean 10 minutes to walk 1 km from his house to Wawa. He stays at Wawa for 5 minutes and then continues on to Shane's You ride your bike home from school by way of your friend’s house. It house. Shane's house is 2.5 km past Wawa. takes you 7 minutes (420 s) to travel It takes Sean 15 minutes to get from Wawa to the 2500 m to his house. You spend Shane's house. Calculate Sean's average 10 minutes there, before traveling speed over the entire trip. 3500 m to your house in 9 minutes (540 s). What was your average speed for this trip? Sep 8­4:20 PM Jun 14­8:50 AM 3

abp_kinematics­presentation for 1819.notebook September 13, 2018 Position and Reference Frames Position and Reference Frames Speed, distance and time didn't require us to define where we started and where we ended up. They just measure how far we traveled and how long it took to travel that far. However, much of physics is about knowing where something is and how its position changes with time. To define position we have to use a reference frame. Return to Table of Contents https://www.njctl.org/video/?v=5mPK2E2GkzA Jun 29­2:17 PM Aug 14­2:24 PM Reference Frame Activity Position and Reference Frames Send a volunteer out of the classroom to wait for further A reference frame lets us define where an object is located, instructions. relative to other objects. Place an object somewhere in your classroom. Write specific directions for someone to be able to locate the object For instance, we can use a map to compare Write them in a way that allows you to hand them to someone the location of different cities, or a globe to who can then follow them to the object. compare the location of different continents. Remember: you can't tell them the name of something your object is near, just how they have to move to get to it. For instance 'walk to the SmartBoard' is not a specific direction. However, not every reference frame is appropriate for every problem. Test your directions out on your classmate, (who is hopefully still in the hallway!) Aug 14­2:24 PM Aug 14­2:24 PM Results ­ Reference Frames Reference Frame Activity ­ Reflection In your groups, make a list of the things you needed to include in your directions in order to successfully locate the You probably found that you needed: object in the room. A starting point (an origin) As a class, discuss your findings. A set of directions (for instance left­right, forward­backward, up­down) A unit of measure (to dictate how far to go in each direction) Aug 14­2:24 PM Aug 14­2:24 PM 4

abp_kinematics­presentation for 1819.notebook September 13, 2018 The Axis 8 All of the following are examples of positive In this course, we will be solving problems in one­dimension. direction except: You'll probably find that you need a starting point (an origin) Typically, we use the x­axis for that direction. A to the right A set of directions (for instance left­right, forward­backward, up­ +x will usually be to the right B north down) C west ­x would then be to the left Answer A unit of measure (how far to go in each direction) ­ x +x D up Usually we'll: E I need help We could define it the opposite way, but unless specified otherwise, this is what we'll assume. We also can think about Define the origin as a location labeled "zero" compass directions in terms of positive and negative. For Three axes: x, y and z for direction example, North would be positive and South negative. The meter as our unit of measure The symbol for position is "x". https://www.njctl.org/video/?v=JnzoLC8tbAE Aug 14­2:24 PM May 9­9:30 PM 9 All of the following are examples of negative direction except: Displacement A to the right B south C west Answer D down E I need help Return to Table of Contents https://www.njctl.org/video/?v=Wm­YzMopcY8 https://www.njctl.org/video/?v=yXc9uj­Qolc May 9­9:30 PM Jun 29­2:17 PM Displacement Displacement +y Displacement describes how far Now that we understand how to define position, we can talk you are from where you started, about a change in position; a displacement . regardless of how you got there. ­x +x The symbol for "change" is the Greek letter "delta" " Δ". So " Δ x" means the change in x or the change in position ­y Aug 14­2:24 PM Aug 14­2:24 PM 5

abp_kinematics­presentation for 1819.notebook September 13, 2018 Displacement Displacement +y +y and then 20 miles back toward For instance, if you drive 60 miles Pennsylvania. from Pennsylvania to New Jersey... x 0 x 0 ­x ­x +x +x x f (In physics, we label the (We also starting label the final ­y position x 0 ) ­y position x f ) Aug 14­2:24 PM Aug 14­2:24 PM Displacement Displacement You have traveled: +y Measurements of distance can only be positive values (magnitudes) since it is impossible to travel a negative a distance of 80 miles , and distance. a displacement of 40 miles , x 0 x f ­x +x since that is how far you are from where you started ­y Imagine trying to measure a negative length with a meter stick... we can calculate displacement with the following formula: Δ x = X f ­ X o Aug 14­2:24 PM Aug 14­2:24 PM Displacement Vectors and Scalars However, displacement can be positive or negative since you can end up to the right or left of where you started. Scalar ­ a quantity that has only a magnitude (number or value) +y +y Vector ­ a quantity that has both a magnitude and a direction Which of the following are vectors? Scalars? ­x x o +x ­x x f x f x o +x Quantity Vector Scalar Time Distance ­y ­y Displacement Speed Displacement is negative. Displacement is positive. Aug 14­2:24 PM Sep 12­2:26 PM 6