# Motion Three Terms to know: Position. This is precisely where an object is located. Speed. Precisely how fast an object is moving. Acceleration. Precisely.

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Motion

Three Terms to know: Position. This is precisely where an object is located. Speed. Precisely how fast an object is moving. Acceleration. Precisely how fast an object's speed is changing. (most challenging for people)

What is Motion? Motion can be described as a change in position. To know whether the position of something has changed, you need a reference point. (Train Example)

Motion and Time Descriptions of motion often include speed motion speedIf you think of motion as a change in position, then speed is an expression of how much time it takes for that change in position to occur

Speed…more definitions Speed is the rate of change in position. Speed can also be described as simply a “rate of motion”

Measuring Speed The speedometer in a car shows instantaneous speed Instantaneous speed is the rate of motion at any given instant.

Average vs. Instantaneous Speed

Speed Triangle/Pyramid

The Equations Distance = Speed x TimeDistance = Speed x Time Speed = Distance / TimeSpeed = Distance / Time Time = Distance / SpeedTime = Distance / Speed

Changing Speed Think about riding a bicycle to your friends house 2 km away You start from a stop. Speed = 0 km/hr You reach a speed of 20 km/hr As you pedal up a steep hill your speed drops to 12 km/hr As you go down the hill your speed increases to 35 km/hr, and you pull into your friend’s driveway You look at your watch and see the trip has taken you 30 minutes How would you express your speed on such a trip? Would you use your fastest time, your slowest time, or some speed in between?

Average Speed In cases where the rate of motion (speed) varies a great deal, the best way to describe speed is to use average speed. Average Speed is the total distance traveled divided by total time of travel So from the last slide: If the total distance was 2 km, and the total time was 30 minutes how fast was the cyclist going?

Example Problem Your neighbor says she can skate at a speed of 4 m/s. To see if you can skate faster, she times you as you skate as fast as you can for 100 m. Your time is 20 seconds. Who skates faster?

Answer 1.What is known/given? Distance, d = 100m Time, t = 20s 2.What is unknown? (what are you trying to find?) Average Speed = ? 3.Choose an equation with the appropriate variables s = d / t 4.Input the values and solve the equation s = 100m / 20 seconds = 5 m/s s = 100m / 20 seconds = 5 m/s

Velocity Speed with a direction… –2 m/s SOUTH –5.6 km/s NORTHWEST

Graphing Speed Distance on the Y-axis Time on the X-axis Title your graphs correctly Label your axes correctly

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