Acceleration is the rate that velocity changes over time.

An object is accelerating if◦ Its speed changes◦ Its direction changes◦ Both its speed and direction change

Speeding up◦ From red light to green light◦ When you are in a car as it speeds up, your body

goes backward. Slowing down

◦ From green light to red light◦ When you are in a car as it slows down, your body

goes forward.

The variable for acceleration is “a.”

a = Δv / t

The units for acceleration are m/s2

If the object’s acceleration is negative, the object is probably slowing down.

A car can get from rest to 27m/s (around 60mph) is 2.5seconds. What was the car’s acceleration?

Given:

Vi = 0

Vf = 27m/s

t = 2.5s

a = (vf – vi) / t

a = (27-0) / 2.5

a = 27 / 2.5

a = 10.8m/s2

Page 375: #1-5 SHOW YOUR WORK!!

Before, we used v = d / t, or d = v x t This equation only works if velocity is

constant (not changing) By definition, velocity changes if an object

is accelerating.

If an object is speeding up,◦ It covers a distance of

V x t plus a little bit. If an object is slowing down,

◦ It covers a distance of V x t minus a little bit.

Instead of the equation we learned when velocity was constant…

We use the following equation when accelerating,

d = vit + ½ at2

Example: A runner accelerates at 1.2m/s2 for 30seconds at the beginning of a race. How far does he travel in those 30 seconds?

d = vit + ½ at2

d = 0 + ½ (1.2)(30)2

d = 540m

Given:

a = 1.2m/s2

t = 30s

Vi = 0