Chapter 11: Section 2 Acceleration
Acceleration and Motion Recall that velocity has both a speed and a direction. Like velocity, acceleration has a value and a direction. When an object undergoes acceleration, its velocity changes. acceleration: the rate at which velocity changes over time.
An object accelerates if its speed, direction, or both change. Acceleration can be a change in speed. An increase or decrease in speed is an acceleration. Acceleration can also be a change in direction. A motorcyclist who rides around the inside of a large barrel is constantly accelerating. A person riding a Ferris wheel at an amusement park is accelerating.
Calculating Acceleration
Calculating Acceleration For straight-line motion, a positive acceleration means that the object’s velocity is increasing—the object is speeding up. Ex. 5.6 m/s2 Negative acceleration means that the object’s velocity is decreasing—the object is slowing down. Ex. -6.89 m/s2 SI Units for Acceleration: m/s2
Let’s Try It! A flowerpot falls off a second-story windowsill. The flowerpot starts from rest and hits the sidewalk 1.5 s later with a velocity of 14.7 m/s. Find the average acceleration of the flowerpot. Given? Unknown?
You Try It! A lizard accelerates from 2 m/s to 10 m/s in 4 seconds. What is the lizard’s average acceleration? A runner covers the last straight stretch of a race in 4 s. During that time, he speeds up from 5 m/s to 9 m/s. What is the runner’s acceleration in this part of the race?
Graphing Acceleration The slope of a straight line on a speed vs. time graph is equal to the acceleration.
Graphing Acceleration Acceleration can also be seen on a distance vs. time graph. The distance vs. time graph is not a straight line when the velocity is not constant. This curved line indicates that the object is under acceleration.
Exit Slip Identify the straight-line accelerations below as either speeding up or slowing down: 5.7 m/s/s -29.8 m/s/s -2.43 m/s/s 9.8 m/s/s