Chapter 2 Motion Section 1 Describing Motion Warmup

Chapter 2: Motion Section 1: Describing Motion

Warm-up: �Compare your maximum speed with that of a cheetah, horse, elephant, and snake. Could you win a race against any of them?

Learning Goals: �Distinguish between distance and displacement. �Explain the difference between speed and velocity. �Interpret motion graphs.

Motion and Position �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 and Displacement �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 40 meters

Speed �Speed: the distance an object travels per unit of time

Calculating Speed �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)

Calculating Speed �Speed = d/t �Distance = �Time =

Calculating Speed 1 �A car traveling at a constant speed covers a distance of 750 m in 25 s. What is the car’s speed?

Calculating Speed 2 �A man runs at a speed of 2. 30 m/s. How long does it take for the man to run 50 m?

Calculating Speed 3 �A car is travelling at 30 km/hr for 125 s. How far does the car travel in meters?

Speed �Average speed: total distance traveled divided by the total time of travel �Instantaneous speed: speed at a given point in time

40 meters 4 s 22 meters 11 s 2 s 10 s 40 meters 22 meters

Graphing Motion �Motion can be shown on a distance vs. time graph Time on x-axis Distance on y-axis

Graphing Motion �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 �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!