Chapter 2: Motion
Compare your maximum speed with that of a cheetah, horse, elephant, and snake. Could you win a race against any of them?
Distinguish between distance and displacement. Explain the difference between speed and velocity. Interpret motion graphs.
A reference point is needed to determine the position of an object. Motion occurs when an object changes position relative to its reference point.
Distance: how far an object has moved Displacement: the distance and direction of an object’s change in position from the starting point The SI unit for distance and displacement is the meter (m).
A runner runs from the start line 50 m north plus 30 m in the opposite direction. What is the distance? What is the displacement?
40 meters 22 meters
Speed: the distance an object travels per unit of time
Speed = distance / time Speed = d/t Distance measured in meters (m) Time measured in seconds (s) Speed measured in meters/seconds (m/s) or kilometers/hour (km/h)
Speed = d/t Distance = Time =
A car traveling at a constant speed covers a distance of 750 m in 25 s. What is the car’s speed?
A man runs at a speed of 2.30 m/s. How long does it take for the man to run 50 m?
A car is travelling at 30 km/hr for 125 s. How far does the car travel in meters?
Average speed: total distance traveled divided by the total time of travel Instantaneous speed: speed at a given point in time
40 meters 22 meters 4 s 11 s 10 s 2 s
Motion can be shown on a distance vs. time graph Time on x-axis Distance on y-axis
On a distance vs. time graph the slope describes the speed Steeper slope = faster speed Horizontal line = zero speed = object at rest
Distance (m) Time (s)
Velocity: includes the speed of an object and the direction of its motion Because velocity depends on direction as well as speed, the velocity of an object can change even when its speed does not!
Car is driving 30 km/hr, but its velocity is constantly changing!
40 meters 22 meters 4 s 11 s 10 s 2 s
Miss Marnik walked a distance of 1.60 km in 30 min. Find her average speed in m/s.