 Chapter 1 Matter in Motion

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Chapter 1 Matter in Motion
Shuey/Wolfe

Things to look for How is motion measured? What is a force?
How does friction affect motion? How does gravity affect objects?

Measuring Motion Observing motion
Motion- When an object changes position over time when compared to a reference point.

Common Reference Points
Reference point- an object that appears to stay in place in relation to an object being observed for motion.

Speed Depends on Distance and Time
Speed- The rate at which an object moves. The SI unit for speed is meters per second (m/s).

Determining Average Speed
Average speed= Total distance Total Time

Recognizing 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 distance Total Time 360km/4h=90km/h

Practice Problem #1 1. If you walk 1.5 hours and travel 7.5 km, what is your average speed? Average speed= Total distance Total Time Average speed = 7.5Km 1.5 hours 7.5/1.5= 5m/s

Practice Problem #2 A 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 distance Total Time Average speed = 25 = 2.4 m/s

Riddle Two 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?

Velocity Velocity- 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 forward km/h m/h south

Velocity 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.

Combining 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?

Determining 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.

Sample Problems A 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?

Acceleration 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

Calculating Acceleration
Acceleration = final velocity- starting velocity time it takes to change velocity Example- 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/s 5S Answer = 1 m/s/s south

Problem #1 A 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 velocity time it takes to change velocity Acceleration= 10,000m/s - 8,000m/s 40S 10, = 2000/40 Answer = 50 m/s/s North

Problem #2 A 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 velocity time it takes to change velocity Acceleration 19.6 m/s – 0m/s 2S 19.6 – = 9.8 m/s/s

Examples of acceleration
Acceleration occurs when velocity increases or decreases. Acceleration in which velocity increases is sometimes called positive acceleration Acceleration 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.

Given the following examples of acceleration state how the velocity changes
A plane taking off Increase in speed A car stopping at a stop sign Decrease in speed Jogging on a winding trail Change in direction Driving around a corner

Circular 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 acceleration Centripetal acceleration-the acceleration that occurs in circular motion an object traveling in a circle is constantly changing directions so acceleration occurs continuously.

Recognizing 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?

Homework Section review page 7 #1-4 Section review page 10 #1-3

Section 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.

Section Review Page 10 What is acceleration?
Does a change in direction affect acceleration? Explain your answer How do you think a graph of deceleration would differ from the one on page 10? Explain your reasoning.

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