Imagine the thrill of riding on a roller coaster like this one! The coaster slowly crawls to the top of the track and then flies down the other side. It also zooms around twists and turns at breakneck speeds. These in and are what make a roller coaster ride so exciting. Changes in or are called .

DEFINING ACCELERATION
is a measure of the change in of a moving object. It measures the rate at which . , in turn, is a measure of the and of motion, so a change in velocity may reflect a change in , a change in , or . Both velocity and acceleration are . A vector is any measurement that has both and People commonly think of acceleration as in in speed, but a in speed is also acceleration. In this case, acceleration is and called . A change in without a change in speed is acceleration as well.

Q: Describe how velocity is changing in each of the motions you identified from the Figure 1.

A: You should describe how both and are changing. For example, the boy on the carousel is moving and and around in a , so his is constantly changing, but his speed changes only at the g and of the ride. The skydiver is falling straight down toward the ground so her direction changing, but her speed keeps as she falls until she opens her parachute.

FEELING ACCELERATION

If you are accelerating, you may be able to feel the change in . This is true whether the change is in , , or . You often feel acceleration when you ride in a car. As the car up, you feel as though you are being against the seat. When the car down, you feel like you are being pushed , especially if the change in speed is . If the car changes and turns , you feel as though you are being pushed to the . With a left turn, you feel a push to the right. The next time you ride in a car, notice how it feels as the car in each of these ways.