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

Acceleration Chapter 9, Section 3

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

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

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

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

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

Calculating Acceleration Acceleration Acceleration Acceleration 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? 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 On your paper, graph the following: On your paper, graph the following: D (m) T (sec) D (m) T (sec)

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

Graph the following on a distance- time graph: D (m)T (s) D (m)T (s)

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

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

Speed-time graphs Using the distance-time graph from the last frame, draw a speed time graph. First fill in the table below: Using the distance-time graph from the last frame, draw a speed time graph. First fill in the table below: Average Speed (m/s) Time (sec) ____0 to 8 ____8 to 12 ____12 to

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

What do the following speed-time graphs depict?

Acceleration Change in velocity Change in velocity Can be change in speed or direction Can be change in speed or direction Acceleration = ∆V/ ∆T Acceleration = ∆V/ ∆T ∆V ∆V at at

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

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

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

Answers: 1. ∆V 80mi/hr a t20mi/hr/s t 4sec = t 2. Yes! Because it’s changing direction! 3. No! It’s not changing speed or direction!

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

Answer: Acceleration = ∆V/ ∆T Acceleration = ∆V/ ∆T Acceleration = Vf – Vi Acceleration = Vf – Vi t a = 20mi/hr – 60mi/hr a = 20mi/hr – 60mi/hr 4 s a = -40mi/hr 4s 4s a = -10mi/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 What is on the y-axis on a distance-time graph? 2. What is constant speed in your own words? 3. What does acceleration mean? 4. If acceleration is negative, what is it called? 5. If a car goes 20 meters in 5 seconds, what is its speed? (Include units!)