MOTION HOW CAN WE TELL IF AN OBJECT

MOTION

HOW CAN WE TELL IF AN OBJECT HAS MOVED? ?

MOTION AND POSITION � Motion: when an object changes its position relative to a reference point � Frame of Reference: a coordinate system in which the position of the objects is measured � Reference Point: where the x-axis and the y -axis of the frame of reference intersect

DISTANCE VS. DISPLACEMENT � Distance: how far an object has moved � Displacement: the distance and direction of an object’s change in position from the starting point

DISTANCE VS. DISPLACEMENT � Can the displacement of an object every be more than the distance an object traveled?

CALCULATING DISPLACEMENT �A squirrel runs 4. 8 m across a lawn, stops and runs 2. 3 m back in the opposite direction. What is the squirrels displacement from its starting point? � Displacement = 4. 8 m – 2. 3 m = 2. 5 m

CALCULATING DISPLACEMENT �A cyclist leaves home and rides due east for a distance of 45 km. She returns home on the same bike path. What is her displacement? � Displacement = 45 km – 45 km = 0 km

SPEED � Speed: the distance an object travels per unit time Speed (s) = distance (d) / time (t)

SPEED metres Speed = distance traveled time taken Metres per second (m/s) seconds

SPEED kilometres Speed = distance traveled time taken Kilometres per hour (km/h) hours

UNITS OF SPEED Unit of Speed Examples of Uses Approximate Speed km/s Rocket escaping Earth’s atmosphere 11. 2 km/s km/h Car Traveling on the highway 100 km/h cm/yr Geologic Plate Movement 2 cm/year – 17 cm/yr

PRACTICE CALCULATING SPEED �A car traveling at a constant speed covers a distance of 750 m in 25 s. What is the car’s speed? � Distance = 750 m � Time = 25 s � s = d/t � 750/25 = 30 m/s

DISTANCE TRAVELED � What if we know the speed of an object and the time it moved for and need to calculate the distance traveled? � speed = distance/time � Distance = speed x time

CALCULATING DISTANCE TRAVELED � Mrs. Cowley’s drive to work takes her 30 minutes. If she drives at an average speed of 80 km/h, what is the distance between the school and her house? �d = s x t � d = 80 km/h x. 5 h � d = 40 km

MOTION WITH CONSTANT SPEED � Constant Speed: no acceleration or deceleration occurs � Average Speed: the speed of motion when speed is changing over time � Instantaneous speed: the speed at a given point in time

LEARNING CHECK � What are 2 examples of motion in which the instantaneous speed changes?

GRAPHING MOTION � Distance-time graph: shows the motion of an object over a period of time Time is plotted on the x-axis � Distance is plotted on the y-axis �

GRAPHING MOTION � Straight line: the object moves with a constant speed � Steeper slope = faster movement � Horizontal line = object is at rest

GRAPHING MOTION � Curved lines: to the right = getting slower, to the left = getting faster

VELOCITY � Velocity: includes the speed AND direction of an object

ACCELERATION � Acceleration: the rate of change of an objects velocity � Acceleration occurs when an object changes speed, direction or both

ACCELERATION EQUATION �a = Vƒ - Vί t � a = acceleration � Vί = initial velocity � Vƒ = final velocity � t = time

PRACTICE PROBLEM �A plane stars at rest on a runway. After 20 seconds the speed of the plane is 80 m/s. Calculate the acceleration of the plane. � a = Vƒ – Vί t � a = 80 m/s – 0 m/s 20 s � a = 4 m/s

PRACTICE PROBLEM �A skateboarder is slowing down to a stop. He is moving at a speed of 3 m/s. He comes to a stop in 2 seconds. Calculate the skaters acceleration. � a = Vƒ – Vί t � a = 0 m/s – 3 m/s 2 s � a = -1. 5 m/s