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Bell Ringer

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What is the velocity of the cheetah? 2. What does it mean for an object to have an acceleration? ... Marissa's car accelerates at an average rate of 2.6 m/s2. ... – PowerPoint PPT presentation

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Title: Bell Ringer


1
Bell Ringer
  • Monday 8/31/09
  • 1. A cheetah ran a distance of 274 m in 8.65s
    toward an antelope. What is the velocity of the
    cheetah?
  • 2. What does it mean for an object to have an
    acceleration?

2
Acceleration
  • Science 1A

3
Changes in Velocity
  • Changes in velocity include
  • Speeding up
  • Slowing down
  • Any change in direction
  • Any change in velocity is called an Acceleration!

4
Acceleration
  • The acceleration of an object then is its change
    in velocity over a certain period of time.

5
  • We calculate acceleration by the following
    equation
  • Acceleration (a)
  • final velocity initial velocity
  • time
  • a Dv
  • t

6
Dv final v initial v
  • The SI unit for acceleration is
  • Meters per second per second
  • m/s2

7
Acceleration Values
  • Acceleration values may be positive or negative.
  • Positive acceleration means that the object is
    speeding up.
  • Negative acceleration means that the object is
    slowing down.

8
Acceleration Values cont.
  • A small acceleration value means that speed is
    increasing or decreasing slowly.
  • A large acceleration value means that speed is
    increasing or decreasing rapidly.

9
Acceleration Cont
  • An object at constant velocity has no
    acceleration it is not speeding up, slowing
    down or changing direction!

10
Lets Practice!
  • 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.

11
  • List the given and unknown values.
  • Given time, t 1.5 s
  • initial velocity, initial v 0 m/s down
  • final velocity, final v 14.7 m/s down
  • Unknown acceleration, a ? m/s2 down

12
  • Write the equation for acceleration.
  • Acceleration (a)
  • final velocity initial velocity
  • time
  • a Dv
  • t

13
  • Insert the known values and solve.
  • a Dv (final v initial v)
  • t t
  • (14.7 m/s 0 m/s)
  • 1.5 s
  • a 14.7 m/s 9.8 m/s2 down
  • 1.5 s

14
Now you get to practice!
15
  • 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.

16
  • 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/s2 along her path

17
  • 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 turtles average
    acceleration?

18
  • 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 turtles average
    acceleration?
  • .075 m/s2 toward the shore

19
  • 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.

20
  • 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/s2 north

21
  • Marissas car accelerates at an average rate of
    2.6 m/s2. Calculate how long it takes her car to
    accelerate from 24.6 m/s to 26.8 m/s.

22
  • Marissas car accelerates at an average rate of
    2.6 m/s2. Calculate how long it takes her car to
    accelerate from 24.6 m/s to 26.8 m/s.
  • 0.85 s

23
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 objects
    speed.

24
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25
  • Data for a Bicycle at Constant Speed

26
  • Data for a Bicycle at Constant Velocity

27
  • Data for a Slowing Bicycle (Speed)

28
  • Data for a Slowing Bicycle

29
Acceleration Lab
  • Work with a partner
  • Read through the directions
  • Get the materials
  • Begin the lab

30
Class work
  • Acceleration Worksheet
  • Acceleration (a) final velocity initial
    velocity
  • time
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