MOTION! CHAPTER 11
To describe motion accurately, a frame of reference is necessary These are objects which are NOT moving with respect to the “moving” object. Some possible frames are -- the interior of the airliner, -- the surface of the Earth, or -- the distant stars with respect to which the Earth rotates and moves.
Relative motion….depends where you are… Relative Motion (frame of reference)
DISTANCE = length between 2 points In science, we use METRICS to measure everything…so start thinking in metrics… 1 m = 100 cm 1 km = 1000 m 10 mm = 1 cm
Displacement is the distance between start and finish… If you walk in a circle, your displacement is ZERO!
VECTORS… A vector is magnitude AND direction. Go north 4 km. Turn around and go south 2 km. Your total displacement is 2 km. Vectors are used to navigate in an airplane or ship. Sometimes you have to fly or sail “around” something.
P. 331 has a nice illustration…
SPEED! Average speed is total distance/total time traveled. m/s Miles/hour Km/hour Etc…… Average speed = total distance = d/t total time
Let’s practice! A person jogs 4 km in 32 min. Then, he jogs 2 km in 22 min. Finally, after a drink of water, he jogs 1 km in 16 min. What is the jogger’s average speed?
A train travels 190 km in 3 hours A train travels 190 km in 3 hours. Then the train speeds 120 km in 2 hours. What is the train’s average speed?
Instantaneous Speed… The speed you are going right this second! A cheetah can be clocked at 90 km/hr!
So, how do you GRAPH speed? The slope of the line on a distance time graph is speed. P. 334 figure 7
VELOCITY is a vector… Speed and direction is aka velocity.
p. 337 Why do you need to know this? If you are on a boat or ski-doo, you can calculate true speed if you add your vectors. (same with an airplane) So, when you fly to LAX, it may take longer than when you fly back to DAY. It’s important for pilots to calculate this to estimate how much fuel they need.
Oh yeah, there’s a big “jet stream” that adds or subtracts true ground speed of the plane.
ACCELERATION! (11.3) Changes in speed Changes in direction Or Changes in both Acceleration is a vector!
What is the acceleration of gravity? 9.8 m/s2
How do you calculate acceleration? change of velocity/total time a = (vf – vi)/t
MATH PRACTICE!!! A car goes 10 m/s starts to decelerate steadily. It comes to a complete stop in 20 seconds. What is its acceleration?
An Airplane travels down a runway for 4 seconds with an acceleration of 9.0 m/s2. What is its change in velocity during this time?
A kid drops a ball from a bridge A kid drops a ball from a bridge. The ball strikes the water under the bridge 2.0 seconds later. What was the velocity of the ball when it strikes the water?
A stupid boy throws a rock straight up into the air A stupid boy throws a rock straight up into the air. It reaches the highest point of its flight after 2.5 seconds. How fast was it going when it left the boy’s hand?
How fast will the rock hit the kid in the eye when it returns to earth?
Confucius say…. Never spit into the wind!