Describing MotionDescribing Motion

Section 2-1Section 2-1

MotionMotion

• Motion occurs when an object changes Motion occurs when an object changes its position.its position.

• Both Both DistanceDistance and and TimeTime are important are important in describing motion.in describing motion.

• Sometimes you know motion has Sometimes you know motion has occurred even if you didn’t see it occurred even if you didn’t see it happen. (mail truck)happen. (mail truck)

• Relative motion: you are moving even Relative motion: you are moving even when you are sitting in your chair. You when you are sitting in your chair. You are moving relative to the other planets.are moving relative to the other planets.

Distance vs. Distance vs. DisplacementDisplacement

• Distance:Distance: How far an object has How far an object has moved (total)moved (total)

• Displacement: Displacement: How far and in what How far and in what direction an object has moved from its direction an object has moved from its start position.start position.

• Figure 2 pg. 39Figure 2 pg. 39

SpeedSpeed

• Speed = the distance an object Speed = the distance an object travels in a given amount of timetravels in a given amount of time

• Speed = Speed = distancedistance

timetime

• SI unit of speed is m/sSI unit of speed is m/s

Calculating speedCalculating speed

• Calculate the speed that you are Calculate the speed that you are running, if you run 400 meters in 72 running, if you run 400 meters in 72 seconds.seconds.

Types of SpeedTypes of Speed• Constant speedConstant speed: speed doesn’t change : speed doesn’t change

(set your car on cruise control)(set your car on cruise control)• Changing speedChanging speed: Riding a bike for 5 : Riding a bike for 5

km. Take off and increase speed, slow km. Take off and increase speed, slow down up hill, speed up down hill, stop down up hill, speed up down hill, stop for stop sign. The trip took you 15 min for stop sign. The trip took you 15 min (.25 h)(.25 h)

• Average speedAverage speed: : total distancetotal distance total timetotal time Instantaneous speedInstantaneous speed: speed at any : speed at any

given moment.given moment.

Graphing motionGraphing motion

• Distance – time graphsDistance – time graphs

• Figure 5 pg. 43Figure 5 pg. 43

VelocityVelocity

• Velocity: includes speed and Velocity: includes speed and DIRECTIONDIRECTION

• Storm is moving at 20km/hr. Should Storm is moving at 20km/hr. Should you be seeking shelter?you be seeking shelter?

• Two trains could be going the same Two trains could be going the same speed, but have different velocities.speed, but have different velocities.

• Race car going around an oval track Race car going around an oval track might have constant speed, but might have constant speed, but different velocities.different velocities.