Acceleration Chapter 8 Section 2 part 1

Changes in Velocity Changes in velocity include:Changes in velocity include: –Speeding up –Slowing down –Any change in direction Any change in velocity is called an Acceleration!Any change in velocity is called an Acceleration!

Acceleration The acceleration of an object then is its change in velocity over a certain period of time.The acceleration of an object then is its change in velocity over a certain period of time. We calculate acceleration by the following equation:We calculate acceleration by the following equation:  Acceleration (a) = final velocity – initial velocity time  a =  v t

The SI unit for acceleration is:The SI unit for acceleration is: –Meters per second per second –m/s 2 VV at  v = final v – initial v

Acceleration Values Acceleration values may be positive or negative.Acceleration values may be positive or negative. Positive acceleration means that the object is speeding up.Positive acceleration means that the object is speeding up. Negative acceleration means that the object is slowing down.Negative acceleration means that the object is slowing down.

Acceleration Values cont. A small acceleration value means that speed is increasing or decreasing slowly.A small acceleration value means that speed is increasing or decreasing slowly. A large acceleration value means that speed is increasing or decreasing rapidly.A large acceleration value means that speed is increasing or decreasing rapidly. An object at constant velocity has no acceleration – it is not speeding up, slowing down or changing direction!An object at constant velocity has no acceleration – it is not speeding up, slowing down or changing direction!

Let’s Practice! Math Skills P 260 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.

List the given and unknown values.List the given and unknown values. –Given: time, t = 1.5 s initial velocity, initial v = 0 m/s down initial velocity, initial v = 0 m/s down final velocity, final v = 14.7 m/s down –Unknown: acceleration, a = ? m/s 2 down Write the equation for acceleration.Write the equation for acceleration.  Acceleration (a) = final velocity – initial velocity time time  a =  v t

Insert the known values and solve.Insert the known values and solve.  a =  v = (final v – initial v) = t t = (14.7 m/s – 0 m/s) = (14.7 m/s – 0 m/s) 1.5 s 1.5 s  a = 14.7 m/s = 9.8 m/s 2 down 1.5 s 1.5 s

Now you get to practice! Do the five practice problems on page 260 # 1-5. HINTS  On # 4, use t =  v a  On # 5, final v = initial v + at

1)Natalie accelerates her skateboard along a straight path from 0 m/s to 4.0 m/s in 2.5 s. Find her average acceleration.  1.6 m/s 2 along her path 2)A turtle swimming in a straight line toward the shore has a speed of 0.50 m/s. After 4.0 s, its speed is 0.80 m/s. What is the turtle’s average acceleration? .075 m/s 2 toward the shore

3)Find the average acceleration of a northbound subway train that slows down from 12 m/s to 9.6 m/s in 0.8 s.  -3 m/s 2 north 4)Marissa’s car accelerates at an average rate of 2.6 m/s 2. Calculate how long it takes her car to accelerate from 24.6 m/s to 26.8 m/s.  0.85 s

5)A cyclist travels at a constant velocity of 4.5 m/s westward, then speeds up with a steady acceleration of 2.3 m/s 2. Calculate the cyclist’s speed after accelerating for 5.0 s.  16 m/s

Motion Graphs When the motion of an object is graphed by plotting the distance it travels versus time, the slope of the resulting line is the object’s speed.

Data for a Bicycle at Constant Velocity

Data for a Slowing Bicycle