Chapter 3 Day 3 Acceleration

GOALS Describe and calculate acceleration.

When studying one dimensional motion Positive acceleration is toward the right. Negative acceleration is toward the left. CAUTION: The direction of acceleration is independent of the direction of motion.

Acceleration Velocity is changing Vector quantity The change in velocity divided by the elapsed time Units: m/s/s or m/s2

Changing speed When the objects velocity and acceleration are in the same direction the object will increase in velocity. When the objects velocity and acceleration are in the opposite directions the object will decrease its velocity..

Solving Problems Given: “I know what values I have.” G.U.E.S.S. method Given: “I know what values I have.” Unknown: “I know where I am going.” Equation: “ I know the physics relationship.” Substitute: “I know how to apply the physics.” Solve: “I know what the answer means.”

Example 1 a=49m/s2 Δt=15s vi = 0 m/s (vf - vi) = aΔt vf = ? m/s A dragster starting from rest accelerates at a rate of 49m/s2. How fast is it going after an elapsed time of 15s? a=49m/s2 Δt=15s vi = 0 m/s vf = ? m/s (vf - vi) = aΔt (vf - 0)=(49m/s2)(15s) vf = 740 m/s

Graphing Acceleration vs. time a (m/s/s) Shows the rate of acceleration and its direction. +a t (s) -a

Stationary v a d t t t

Constant velocity v a d t t t

Accelerating v a d t t t