Motion and SpeedMotion and Speed

Describing MotionDescribing Motion

MotionMotion

Distance and time are important in Distance and time are important in describing motion.describing motion.

MotionMotion occurs when an object changes occurs when an object changes position.position.

You need a reference point to describe You need a reference point to describe motion.motion.

A reference point helps determine how far A reference point helps determine how far and what direction something has moved.and what direction something has moved.

Relative MotionRelative Motion

Motion is relative.Motion is relative. Is the door to the classroom moving?Is the door to the classroom moving? YES!!! The door is not moving relative to YES!!! The door is not moving relative to

you or your desk or the building, but it is you or your desk or the building, but it is moving when compared to the sun and moving when compared to the sun and other planets.other planets.

Motion is relativeMotion is relative

DistanceDistance

DistanceDistance is how far an object has moved is how far an object has moved TOTALTOTAL..

The SI unit of distance is the meter The SI unit of distance is the meter (kilometer, centimeter, etc.)(kilometer, centimeter, etc.)

Distance is very important in describing Distance is very important in describing motion.motion.

DisplacementDisplacement

Displacement Displacement is the distance AND direction is the distance AND direction of an objects change in in position from the of an objects change in in position from the starting point.starting point.

A running back in football may run 26 yards A running back in football may run 26 yards but only gain 13 yrds from the line of but only gain 13 yrds from the line of scrimmage.scrimmage.

ALWAYS include DIRECTION when ALWAYS include DIRECTION when describing displacement (20m NORTH)describing displacement (20m NORTH)

SpeedSpeed

SpeedSpeed is the distance an object travels per is the distance an object travels per unit of time.unit of time.

70 Miles per hour70 Miles per hour You must always include distance and time You must always include distance and time

when describing speed.when describing speed.

RateRate

RateRate is any change over time. is any change over time. Rate of growth = how much you grow in X Rate of growth = how much you grow in X

amount of time.amount of time.

Calculating SpeedCalculating Speed

Speed = Distance / TimeSpeed = Distance / Time S=D/TS=D/T So if you ran 2 km in 10 mins?????So if you ran 2 km in 10 mins?????

S= 2/10S= 2/10 Speed = .2 km per hrSpeed = .2 km per hr m/s….cm/s…mi/hr… etcm/s….cm/s…mi/hr… etc

Motion w/ Constant SpeedMotion w/ Constant Speed

If your in a car on an empty freeway with the If your in a car on an empty freeway with the cruise set at 70 miles/hr…. Your at a cruise set at 70 miles/hr…. Your at a CONSTANT speed.CONSTANT speed.

No change in speed means that you can No change in speed means that you can calulate speed over any distance (mm to calulate speed over any distance (mm to miles it is all the same)miles it is all the same)

Changing SpeedChanging Speed

Most of the time we are not at a constant Most of the time we are not at a constant speed.speed.

In a car the speed limits change going In a car the speed limits change going through towns.through towns.

You slow down to turnYou slow down to turn Speed up to pass. Etc.Speed up to pass. Etc. How do you express speed that is not How do you express speed that is not

constant????????constant????????

Average SpeedAverage Speed

Average SpeedAverage Speed is the total distance traveled is the total distance traveled divided by the total time of travel.divided by the total time of travel.

Average speed= total distance/total timeAverage speed= total distance/total time SOOOOOOOOOOSOOOOOOOOOO If you traveled 5km in .25 hours…. What If you traveled 5km in .25 hours…. What

would your average speed be?would your average speed be? 5/.25=?????5/.25=????? 20 km/h20 km/h

Instantaneous SpeedInstantaneous Speed

Instantaneous SpeedInstantaneous Speed is the speed at a given is the speed at a given point in time.point in time.

A speedometer shows instantaneous speedA speedometer shows instantaneous speed If an object is speeding up or slowing down If an object is speeding up or slowing down

the I.S. is always different.the I.S. is always different. If an object is staying at the same speed, it’s If an object is staying at the same speed, it’s

I.S. is always the sameI.S. is always the same

Graphing MotionGraphing Motion

A distance-time graph makes it possible to A distance-time graph makes it possible to display the motion of an object over time.display the motion of an object over time.

Page 43 in booksPage 43 in books

VelocityVelocity

VelocityVelocity describes the Speed describes the Speed ANDAND direction direction of motion of an object.of motion of an object.

There’s a tornado 6 miles west of WF and is There’s a tornado 6 miles west of WF and is traveling at 30 miles per hour… are we in traveling at 30 miles per hour… are we in danger???danger???

We’re not sure… we need to know what We’re not sure… we need to know what direction the tornado is traveling…direction the tornado is traveling…

If east… we take shelter… if west… we’re If east… we take shelter… if west… we’re OKOK

Velocity (cont.)Velocity (cont.)

If your driving 60 mph east and pass If your driving 60 mph east and pass someone who is driving 60 mph west, your someone who is driving 60 mph west, your speeds are the same but your velocities are speeds are the same but your velocities are different because your moving in different different because your moving in different directions.directions.

Velocity can change even if the speed is Velocity can change even if the speed is constant.constant.

It can also change if the direction is It can also change if the direction is constant.constant.

We’re doneWe’re done