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Bell Ringer 1. 2. 3. 4. 1 -13 -10 Give me an example of a unit that measures distance. What ALWAYS needs to go at the top of your graph? What is the formula for acceleration? A football field is about 100 meters long. If it takes a person 20 seconds to run its length, what is the speed of the runner? (You may use your formula sheet. )

More Speed Problems 1. The pitcher’s mound in baseball is 85 m from the plate. It takes 4 seconds for a pitch to reach the plate. How fast is the pitch? 2. A runner covers a distance of 120 m in a time of 80 seconds. What is the runner’s speed?

Objectives l ALCOS Objective # 1 l Identify steps within the scientific process l Applying process skills to interpret data from graphs. l ALCOS Objective # 8 l Identify Newton’s three laws of motion.

Acceleration Chapter 9, Section 3

What is acceleration? l Acceleration is the rate at which velocity changes. l In other words, acceleration means “the process of speeding up. ”

Recall… l What is velocity? l Velocity describes both speed and direction. l In science, acceleration refers to increasing speed, decreasing speed, or changing direction.

l When an object speeds up, it is accelerating. l When an object slows down, it is known as deceleration. (or negative acceleration)

Formula l If direction stays the same… l Acceleration = change in speed time l Acceleration = Final speed – initial speed time

What are the units? l If speed is measured in m/s, acceleration is measured in m/s 2.

Calculating Acceleration l As a roller coaster car starts down a slope, its speed is 4 m/s. But 3 seconds later, at the bottom, its speed is 22 m/s. What is its average acceleration?

Distance-time graphs l On your paper, graph the following: l D (m) 0 5 10 15 T (sec) 0 7 14 21

Was your graph a straight line? l A distance-time graph which is a straight line indicates constant speed. l In constant speed, the object does not speed up or slow down. The acceleration is zero.

Graph the following on a distance-time graph: l D (m) 0 5 20 45 80 125 T (s) 0 1 2 3 4 5

Was your graph a curve? l A graph that curves on a distance-time graph shows that the object is accelerating.

Distance-time graphs l Describe the motion of the object as shown in the graph. From 0 -8 sec, constant speed: (25 m/sec); From 8 -12 sec, no motion; From 12 -16 sec, acceleration; From 16 -20 sec, constant speed

Speed-time graphs l Using the distance-time graph from the last frame, draw a speed time graph. First fill in the table below: Average Speed (m/s) ____ 25 ____ 0 37. 5 Time (sec) 0 to 8 8 to 12 12 to 20

What does your graph look like? l Constant speed will be a horizontal line on a speed time graph. l If the speed decreases, the line will slant down. l If the speed increases, the line will slant up.

What do the following speed-time graphs depict?

Acceleration l Change in velocity l Can be change in speed or direction l Acceleration ∆V l a t = ∆V/ ∆T

Acceleration problem l A roller coaster’s velocity at the top of a hill is 10 m/s. Two seconds later it reaches the bottom of the hill with a velocity of 26 m/s. What is the acceleration of the roller coaster?

Answer l Acceleration = ∆V/ ∆T l a = 26 m/s – 10 m/s 2 s a = 16 m/s 2 s a = 8 m/s/s or 8 m/s 2 Calculating Acceleration

More acceleration problems l 1. A car accelerates at a rate of 20 mi/hr/s. How long does it take to reach a speed of 80 mi/hr? l 2. A car travels at 60 miles per hour around a curve. Is the car accelerating? l 3. A car travels in a straight line at 60 mi/hr. Is the car accelerating?

Answers: 1. ∆V a t 80 mi/hr 20 mi/hr/s t 4 sec = t 2. Yes! Because it’s changing direction! 3. No! It’s not changing speed or direction!

Deceleration l Negative acceleration l Example: A car slows from 60 mi/hr to 20 mi/hr in 4 seconds. What is its acceleration?

Answer: l Acceleration = ∆V/ ∆T l Acceleration = Vf – Vi t l a = 20 mi/hr – 60 mi/hr 4 s a = -40 mi/hr 4 s a = -10 mi/hr/s

Review: Distance-time graph of acceleration

Distance-time graph of deceleration

Review: Speed-time graph of acceleration

Review: Speed-time graph of deceleration

Review: Distance-time graph of constant speed

Exit Quiz 1 -13 -10 1. 2. 3. 4. 5. What is on the y-axis on a distance-time graph? What is constant speed in your own words? What does acceleration mean? If acceleration is negative, what is it called? If a car goes 20 meters in 5 seconds, what is its speed? (Include units!)