Chapter 11: MotionChapter 11: MotionSection 1: Describing Motion

MotionMotion

Motion occurs when: ◦an object moves a

certain distance in a certain amount of time◦an object’s position

changes

DistanceDistanceDistance is how far something has movedMeasured in METERS, km, cm, mm, etc.

DisplacementDisplacement

Displacement is the change in position of an object

Also measured in METERS, km, cm, mm, etc.

SpeedSpeed

Speed is the distance an object travels over the amount of time it takes to travel

Measured in m/s (meters per second)Speed (m/s) = distance (m) ÷ time (s)

Calculating SpeedCalculating Speed1. After driving for exactly 60 seconds, you

have driven 600 meters. What speed were you driving?

2. After driving for 1 hour, you have driven 72 kilometers. What speed were you driving?

a. Calculate the speed in km/hrb. Calculate the speed in m/s

Constant & Changing SpeedConstant & Changing Speed

Constant speed means an object does not speed up or slow down.

Changing speed means an object gets faster or slower.

Average SpeedAverage Speed We usually calculate the average speed:

Average speed (m/s) = total distance (m) ÷ total time (s)

Yesterday, John Doe ran 6 km in 30 minutes. Sometimes he sped up and sometimes he slowed down. What was his average speed?

a. Convert 6km to m: 6km x 1000m/1km = 6000 mb. Convert 30 mins to sec: 30 min x 60sec/1min = 1800

secc. Calculate avg. speed: 6000 m ÷ 1800 sec = 3.33m/s

Instantaneous SpeedInstantaneous SpeedSpeed can be

measured at a certain point in time.

For instance, if you are driving, your speedometer may read 30 mi/hr.

You don’t have to drive for an hour for your car to know this – your speed is instantaneous.

Graphing SpeedGraphing Speed

Distance and Time are variables!◦Independent

Variable: time◦Dependent Variable:

distance

Graphing Constant SpeedGraphing Constant Speed

Graphing Changing SpeedGraphing Changing Speed

Graphing Changing SpeedGraphing Changing Speed

Graphing Changing SpeedGraphing Changing Speed

VelocityVelocityVelocity is a measure of an object’s

SPEED and DIRECTION.Velocity is measured by:

velocity = displacement ÷ time

v = d/t

Velocity & DisplacementVelocity & Displacement

If you run around a circular track and end up in the same position you started, your displacement is 0.

So is your velocity: v = 0/time, so v=0

Calculating VelocityCalculating Velocity

1. You walk down a winding road and end up 80 meters from your starting point. It took 1 minute and 20 seconds to walk from one end to the other. What was your velocity?

2. Was your speed greater or less than the velocity you calculated in #1?