Define the term motion. Give an example of something in motion. How do we know an object is in motion? How do we know if we are in motion even if our eyes are closed?
How does a speed-o-meter tell how fast a car is going? How can you tell how fast a sprinter runs? Online Accounts Help! S-10
SPS8 Students will determine relationships among force, mass, and motion. a. Calculate velocity and acceleration.
What is needed to describe motion completely? How are distance and displacement different? How do you add displacements?
How do we know an object is moving? Frame of reference Motion is always relative (compared to) something That something is called the Frame of Reference for us usually the earth)
How do we know an object is moving? Frame of reference We choose a frame that makes sense. Using the ground as a frame, the ball is moving forward Using the truck as a frame of reference, the ball goes up then back down
Distance – the length of a path between two points Displacement – straight line distance (and direction) between the start and end Example: Travel 3.5 miles south
PHET Vector Addition PHET Vector Addition Adding Displacements (vector addition) Vector – has number value and direction If the vectors aren’t in a straight line, then we have to use trigonometry to add the vectors
A walrus scoots 10 m east, then 2 m west, what is his displacement? The same walrus scoots 10 m north, then 2 m west, what is his displacement? S-11
How are instantaneous speed and average speed different? How can you find the speed from a distance-time graph? How are speed and velocity different? How do velocities add?
SR-71 Blackbird Speed: 2070 mph or 920 m/s Speed – ratio of distance to time Measured in meters per second (m/s) Average Speed Example: A car travels 25 km in 0.2 hours, then 45 km in 0.3 hours. What is the average speed? Total distance and then total distance
Practice: A person jog 400 meters in 192 seconds, then 200 meters in 132 seconds, and finally 100 meters in 96 seconds. What is the joggers speed?
Practice: A train travels 190 kilometers in 3.0 hours, and then 120 kilometers in 2.0 hours. What is its average speed?
The fastest car in the world travels at m/s. How long would it take to go 4 km? (4000 m) S-12
Daniel Ling ran the fastest marathon ever (42km or 42,000 m) in a time of 2 hours, 46 minutes and 31 seconds (9991S). A. What was his average speed? B. At that pace, how long would it take to cover a football field (92 m) S-13
A speedometer does not measure average speed, it measures instantaneous speed.
A distance time graph can be used to determine speed. The slope of the graph (distance divided by time) is average speed Gizmo Distance vs. Time
Velocity – speed in a direction (vector) Velocity changes with either A change in speed A change in direction Velocity is added by vector addition (like displacement)
The green sea turtle can run up to 6.22 m/s. A. How far would a green sea turtle get running for 118 s? B. How long would it take a green sea turtle to run a marathon (42,000m)? S-14
The fastest animal in the world is a Cheetah. They can run 100 m in 3.21s. A. What is the speed of a Cheetah? B. How long would it take a Cheetah to run a 40m dash? S-15
How are changes in velocity described? How can you calculate acceleration? How does a speed-time graph indicate acceleration? What is instantaneous acceleration?
Acceleration is a change in velocity, so Change in speed ▪ Either getting faster ▪ Or getting slower Change in direction ▪ Turning Measured in meters per second squared (m/s 2 )
Calculating Acceleration – divide the change in velocity (speed) by the total time Example: A ball rolls down a ramp, starting from rest. 4 seconds later, it’s velocity is 13 m/s. What is the acceleration of the ball? First, what is the initial velocity? 0 m/s
Practice Problem 1 A car traveling at 10 m/s slows down to 3 m/s in 20 seconds. What is the acceleration?
Practice Problem 2 An airplane travels down a runway for 4.0 seconds with an acceleration of 9.0 m/s 2. What is its change in velocity during this time?
Reading a Speed-Time graph The slope of the graph (rise over run) is the acceleration Straight upward – positive constant acceleration Straight downward – negative constant acceleration (slowing down) Flat – constant speed, no acceleration Curved – changing acceleration
A cat is chasing a really cute mouse. A. If the mouse goes from 2 m/s to 11 m/s, what is his v? B. If it took him 4 s to speed up, what is his acceleration? C. If he could keep up that acceleration for 120 s (2 min) how fast would he be going? S-17
The worlds ugliest dog is running away from home. A. As he runs, he accelerates at 1.75 m/s 2 for 3.1s. What is his change in speed? B. If he was originally running at 4 m/s, how fast is he running now? S-18
How does gravity cause acceleration?
Free Fall – when an object is falling under only the influence of gravity The acceleration due to gravity on the surface of the earth is 9.80 m/s 2 So our acceleration equation becomes Everything else is the same
This strange looking thing falls off a cliff and falls for 12 s. What is his change in speed? S-19 I can Calculate using the acceleration due to gravity
Extreme free falling could be fun – unless you forget the parachute. This man will fall for a total of 147 s. How fast would he be going if there was no air friction and he starts with a speed of 0? S-20 I can Calculate using the acceleration due to gravity
Problem 1 How fast will a rock dropped from the top of the empire state building be going after 8.0 seconds?
Bob drives his car 12 m in 3 seconds, then 25 m in 5 seconds. What is his average speed? S-21 I can Calculate using the average speed of an object.
A man walks 18 m east, then 24 m west. What is his displacement. While he is walking west at 5 m/s, a car blows by him going 45 m/s west. What is the relative speed of the car compared to the man? S-22 I can calculate the displacement and relative speed of an object.
Have a fun test S-22 I can calculate the displacement and relative speed of an object.