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

Speed Speed = distance traveled time taken kilometres 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