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Motion and Speed

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**MOTION Motion occurs when an object changes it’s position**

To know whether the position of something changed, you need a reference point (fixed point)---helps determine how far something has moved

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**DISTANCE Distance can be used to describe how far something had moved**

SI unit for distance is the meter

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DISPLACEMENT Displacement is the distance and direction of an object’s change in position from the starting point

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SPEED Speed is the distance an object travels per unit of time (how fast something is moving)

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CALCULATING SPEED In order to calculate the speed of something you must know the distance the object traveled and the time it took to travel that distance

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**CALCULATING SPEED time t**

Speed = distance = d time t Ex: Suppose you run 2 km in 10 min. Your speed would be calculated by: s = d = 2 km = .2 km/min t min

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**CALCULATING SPEED Practice Problems:**

A runner sprints the 100 meter dash in 12.7 seconds. What is her speed? A car traveled from Baton Rouge to Houston. The distance is 606 miles and the trip was made in 5 hours. At what speed was the car traveling?

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CALCULATING SPEED A car is traveling from New Orleans to Lafayette at a constant speed of 55 miles per hour. It took the car 3 hours to make the trip. What distance did the car travel? A car is traveling at a constant speed of 72 mph. The distance between point a and b is 407 mile. How long did it take the car to get to point b?

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CHANGING SPEED You start out on a bike ride traveling 5km total—as you start your speed increases from 0 km/h to 20 km/hr. You slow down to 10 km/h as you go up a hill and then speed up to 30 km/hr. You stop for a red light then move at a constant speed for a while and at the end of the trip you slow down then stop. You traveled for 15 min. How would you calculate your speed???

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CHANGING SPEED Average speed: the total distance traveled divided by the total time of travel Ex: Bike traveled a total of 5km in 15 min (.25 hours) s = d = 5 km = 20 km/h t h

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CHANGING SPEED A car traveled 25 miles. It started at 0 miles per hour and reached 25 miles per hour before coming to a stop sign. It then traveled at a constant speed of 35 miles per hour until it reached it’s destination where it slowed down and stopped. The travel time was 40 min. What was the car’s speed?

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SPEED Instantaneous speed: the speed at a given point of time

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GRAPHING MOTION Distance-time graph (AKA position time graph)show the motion of an object over a period of time

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**GRAPHING MOTION Straight line represents a constant speed (blue line)**

Steepness of a line represents the slope (speed) Crooked line represents a speed that is not constant (red line) There was a time where the runner rested for 7 minutes

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**GRAPHING MOTION Plotting a distance-time graph:**

Distance is plotted on vertical axis (y-axis) Time is plotted on horizontal axis (x-axis) Must have a scale that covers the distance traveled and the time traveled

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GRAPHING MOTION The following data was obtained for two runners. Make a distance-time graph that shows the motion of both runners. Time (s) 1 2 3 4 Sally’s distance (m) 6 8 Jake’s distance

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**GRAPHING MOTION Questions about your graph:**

What is the average speed of each runner? Which runner stops briefly

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**VELOCITY Speed only describes how fast something is going**

Velocity includes the speed of an object and the direction of it’s motion Velocity can change even if the speed of an object remains constant.

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VELOCITY Escalators have the same speed but different velocities because they are traveling in opposite directions.

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ACCELERATION Section 2

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**ACCELERATION Acceleration is the rate of change of velocity**

Occurs when an object slows down, speeds up, changes direction or all of these.

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**ACCELERATION—speeding up and slowing down**

If a car slows down or speeds up it has acceleration If the car goes faster, speed increases and acceleration is positive If the car slows down, speed decreases and the acceleration is negative Acceleration Animation

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**ACCELERATION—Changing Direction**

Any time a moving object changes direction, it’s velocity changes and it is accelerating Carousel is accelerating b/c it is constantly changing direction

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**CALCULATING ACCELERATION**

Acceleration = change in velocity (speed) time Change in velocity = final vel. – initial vel. ACCELERATION a = (vf – vi) t Units of Acceleration m/s2 (meters per second squared)

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**ACCELERATION-positive**

A jetliner starts at rest at the end of a runway and reaches a speed of 80 m/s in 20 seconds. The liner is traveling in a strait line down the runway, so its speed and velocity are the same. What is its acceleration?

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**ACCELERATION--negative**

A skateboarder is moving in a strait line at a speed of 3 m/s and comes to a stop in 2 seconds. The final speed is zero and the initial speed was 3 m/s. What is the skateboarders acceleration?

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**CALCULATING ACCELERATION**

A swimmer speeds up from 1.1 m/s to 1.3 m/s during the last 20 seconds of a workout. What is the swimmer’s acceleration during this time interval?

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**CALCULATING ACCELERATION**

While walking to school you approach an intersection and slow down from 2 m/s to a stop in 3 seconds. What was your acceleration during this time interval?

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**Practice Problems Vi= 0 m/s Vi= 23.8 m/s Vf= 18 m/s Vf= 15 m/s T= 3 s**

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