2Things to look for How is motion measured? What is a force? How does friction affect motion?How does gravity affect objects?
3Measuring Motion Observing motion Motion- When an object changes position over time when compared to a reference point.
4Common Reference Points Reference point- an object that appears to stay in place in relation to an object being observed for motion.
5Speed Depends on Distance and Time Speed- The rate at which an object moves.The SI unit for speed is meters per second (m/s).
6Determining Average Speed Average speed= Total distanceTotal Time
7Recognizing Speed on a Graph Open text to page 5.The distance traveled every hour is different because the speed is not constant .How can the average speed be calculated?Average speed= Total distanceTotal Time360km/4h=90km/h
8Practice Problem #11. If you walk 1.5 hours and travel 7.5 km, what is your average speed?Average speed= Total distanceTotal TimeAverage speed = 7.5Km1.5 hours7.5/1.5= 5m/s
9Practice Problem #2A Bird flies at a speed of 15 m/s for 10 s, 20m/s for 10s, and 25m/s for 5s. What is the birds average speed?Average speed= Total distanceTotal TimeAverage speed =25= 2.4 m/s
10RiddleTwo birds leave the same tree at he same time. They both fly at 10km/h for 1 hour, 15km/h for 30minutes, and 5 km/h for 1 hour. Why don’t they end up at the same destination?
11VelocityVelocity- The speed of an object in a particular direction is the object’s Velocity.Speed and Velocity do not mean the same thing since velocity must include a direction.Which of the following are examples of velocity?m/s forwardkm/hm/h south
12Velocity changes as Speed or Direction Changes You can think of velocity as the rate of change of an objects position. ( constant velocity is always in a straight line)An objects velocity will change if either its speed or direction changes.
13Combining Velocities Textbook page 7. If you are a passenger on a bus traveling at a velocity of 15 m/s east and you stand up and walk down the aisle are you still moving at the same velocity as the bus?
14Determining Resultant Velocity Resultant velocity- The combination of two or more velocities.When combing velocities in the same direction add.When combing velocities in the opposite direction subtract the smaller velocity from the larger.
15Sample ProblemsA bus is traveling 17m/s East. Jack stood up and walked towards the front of the bus traveling 1 m/s. What is his resultant velocity?A bus is traveling 17m/s West. Jack stood up and walked towards the rear of the bus at 2 m/s. What is his resultant velocity?
16Acceleration the rate is which velocity changes. Acceleration-the rate at which velocity changes; an object accelerates if its speed changes, if its direction changes or if both its speed and direction change.Acceleration Tim and Moby
17Calculating Acceleration Acceleration = final velocity- starting velocitytime it takes to change velocityExample- You get on your bicycle and accelerate southward at a rate of 1 m/s/s. After 5 seconds your final velocity is 5 m/s. What was your acceleration?Acceleration = 5m/s – 0m/s5SAnswer = 1 m/s/s south
18Problem #1A plane passes over Point A with a velocity of 8,000 m/s north. Forts seconds later it passes over Point B at a velocity of 10,000 m/s north. What is the plan’s acceleration from A to B?Acceleration = final velocity- starting velocitytime it takes to change velocityAcceleration= 10,000m/s - 8,000m/s40S10, = 2000/40 Answer = 50 m/s/s North
19Problem #2A coconut falls from the top of a tree and reaches a velocity of 19.6 m/s when it hits the ground. It takes 2 seconds to reach the ground/ What is the coconut’s acceleration?Acceleration = final velocity- starting velocitytime it takes to change velocityAcceleration 19.6 m/s – 0m/s2S19.6 – = 9.8 m/s/s
20Examples of acceleration Acceleration occurs when velocity increases or decreases.Acceleration in which velocity increases is sometimes called positive accelerationAcceleration in which velocity decreases is sometimes called negative acceleration or deceleration.Change in direction is also acceleration even is there is no change in speed.
21Given the following examples of acceleration state how the velocity changes A plane taking offIncrease in speedA car stopping at a stop signDecrease in speedJogging on a winding trailChange in directionDriving around a corner
22Circular Motion Continuous Acceleration Is standing on the earths equator an example of acceleration?Yes since you are traveling in a circle as the earth rotates.An object traveling in a circular motion is always changing its direction therefore its velocity is always changing. This is known as centripetal accelerationCentripetal acceleration-the acceleration that occurs in circular motion an object traveling in a circle is constantly changing directions so acceleration occurs continuously.
23Recognizing acceleration on a graph Turn to page 10 in text.The graph shows your acceleration on a roller coaster for the 10 seconds coming down a hill.Is the acceleration positive or negative?Is the acceleration constant?
25Section Review Page 7 What is a reference point? What two things must you know to determine speed?What is the difference between speed and velocity?Explain why it is important to know a tornado’s velocity and not just it’s speed.
26Section Review Page 10 What is acceleration? Does a change in direction affect acceleration? Explain your answerHow do you think a graph of deceleration would differ from the one on page 10? Explain your reasoning.