How do you know you are moving? use a reference point = place/object used for comparison you are moving when your position relative to reference point changes Good reference point: stationary object – it doesn’t move in relation to the Earth You might be moving or not at the same time!!! It depends on the reference point you use. Can you think of an example of it?
Average Speed how fast you go in a period of time rate = the amount of something that changes /occurs in a certain amount of time speed (m/s) = distance (m/km) time (s/h) Unit: m/s or km/h
Practice A cyclist travels 30km in 3 hours. What is his average speed? An ant moves 5 cm in 2 seconds. What is its average speed? The fastest car in the world, the SSC Ultimate Aero, would be able to travel 1505 km in 3.5 hours. What is its average speed? http://br.youtube.com/watch?v=b5zqKWZ-38E Curious facts: Top speed of a human = 40 km/h Fastest dog – greyhound = 64 km/h Fastest fish – sailfish = 109 km/h Fastest bird – peregrine falcon = 439 km/h Fastest land animal = cheetah 112 km/h
Average Speed x Instant Speed Speed is not usually constant = average Do you travel at the same speed the whole time you are driving from your house to the school? Practice: A cyclist travels 32km during the first 2 hours then 13km during the next hour. What is his average speed?
Displacement Minimal distance between 2 points Two towns: A and B 10 km apart Joined by a railway line that is straight, and goes through the hill in a tunnel Joined by a road that goes around the hill – length= 25 km Distance x displacement Distance = 25 km Displacement = 10 km east What happens if you go from A to B and back again?
Velocity What happens when you hear someone saying a storm is traveling at a speed of 25km/h. Should you prepare for it? It depends on the direction! speed + direction = VELOCITY You can say: the storm is moving 25km/h eastward. Why is it important to know the velocity of certain objects? Air traffic controllers must keep track of airplanes. Speed and direction are important!!!
Graphing Speed The steepness = SLOPE = tells you how fast something changes in relation to the other variable The steeper the slope, the greater the speed SLOPE = rise or (y2 – y1) run (x2 – x1)
Interpret the Graph
Interpret the Graph B C A E D
Acceleration Motion doesn’t usually stay the same the whole time. Imagine a soccer game: the player kicks the ball. The ball speeds up and slows down as it travels away from him until it stops. When it speeds up = accelerate When it slows down = decelerates/negative acceleration Acceleration = rate at which velocity changes
What happens with the speed?
Calculating Acceleration A = final speed – initial speed time Unit: m/s2 or m/s/s An airplane is taking off from Guarulhos Airport. It takes 5 seconds for the airplane to reach the speed of 40 m/s. Calculate the airplane’s acceleration.