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Force and Motion Standards

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Title: Speed, Velocity, and Acceleration Author: Bishop Last modified by: CCSUSER Created Date: 5/9/2009 12:29:49 PM Document presentation format – PowerPoint PPT presentation

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Title: Force and Motion Standards


1
Force and Motion Standards
  • S8P3 Students will investigate the relationship
    between force, mass, and the motion of objects.
  • a. Determine the relationship between velocity
    and acceleration.
  • b. Demonstrate the effect of balanced and
    unbalanced forces on an object in terms of
    gravity, inertia, and friction.

2
  • S8P3 Students will investigate the relationship
    between force, mass, and the motion of objects.
  • a. Determine the relationship between velocity
    and acceleration. Additional vocabulary
    reference point, meter, speed, average speed,
    instantaneous speed, slope, distance,
    displacement
  • b. Demonstrate the effect of balanced and
    unbalanced forces on an object in terms of
    gravity, inertia, and friction. Additional
    vocabulary newton, net force, mass, weight

3
Force and Motion Standards
  • S8P5 Students will recognize characteristics of
    gravity, electricity, and magnetism as major
    kinds of forces acting in nature.
  • a. Recognize that every object exerts
    gravitational force on every other object and
    that the force exerted depends on how much mass
    the objects have and how far apart they are.

4
What do we need to know and be able to do?
5
Essential Question
  • How would you describe how fast an object is
    moving?
  • Supporting Questions
  • How is it possible to be accelerating and
    traveling at a constant speed?
  • Why is it more important to know a tornados
    velocity than its speed?

6
Speed, Velocity, and Acceleration
7
Goals
  • To investigate what is needed to describe motion
    completely.
  • To compare and contrast speed and velocity.
  • To learn about acceleration.

8
To describe motion accurately and completely, a
frame of reference is needed.
9
An object is in motion if it changes position
relative to a reference point.
  • Objects that we call stationarysuch as a tree, a
    sign, or a buildingmake good reference points.

The passenger can use a tree as a reference point
to decide if the train is moving. A tree makes a
good reference point because it is stationary
from the passengers point of view.
10
Describing Motion
Whether or not an object is in motion depends
on the reference point you choose.
11
Distance
  • When an object moves, it goes from point A to
    point B that is the DISTANCE it traveled. (SI
    unit is the meter)
  • Distance is how much ground an object has covered
    during its motion.

B
A
12
Displacement
  • Knowing how far something moves is not
    sufficient. You must also know in what direction
    the object moved.

  • Displacement is how
  • far our of place the
  • object is it is the
  • objects overall
  • change in position.

13
Speed
  • Calculating Speed If you know the distance an
    object travels in a certain amount of time, you
    can calculate the speed of the object.

What is instantaneous speed? Instantaneous
speed is the velocity of an object at a certain
time.
Speed Distance/time
Average speed Total distance/Total time
14
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15
Describing Motion
2.1
Velocity
Because velocity depends on direction as well as
speed, the velocity of an object can change even
if the speed of the object remains constant.
The speed of this car might be constant, but its
velocity is not constant because the direction of
motion is always changing.
16
Velocity
  • Velocity is a description of an objects speed
    and direction.

As the sailboats direction changes, its velocity
also changes, even if its speed stays the same.
If the sailboat slows down at the same time that
it changes direction, how will its velocity be
changed?
17
Speed v. Velocity
  • How are speed and velocity similar?
  • They both measure how fast something is moving
  • 2. How are speed and velocity different?
  • Velocity includes the direction of motion and
    speed does not (the car is moving 5mph East)
  • Is velocity more like distance or displacement?
    Why?
  • Displacement, because it includes direction.

18
Graphing Speed
D I S T A N C E
Speed increasing
Object begins moving at a different speed
Object is stopped
T I M E
19
The steepness of a line on a graph is called
slope.
  • The steeper the slope is, the greater the speed.
  • A constant slope represents motion at constant
    speed.

Using the points shown, the rise is 400 meters
and the run is 2 minutes. To find the slope, you
divide 400 meters by 2 minutes. The slope is
200 meters per minute.
20
Formula for Calculating SpeedSpeed Distance
time

21
Problem Solving Calculating Speed
What is the speed of a sailboat that is traveling
120 meters in 60 seconds? Step 1 Decide what
the problem is asking? A boat traveled 120 meters
in 60 seconds. What was the speed of the
boat? Step 2 What is the formula to calculate
speed? Speed Distance/Time Step 3 Solve
the problem using the formula Speed 120
meters 60 seconds 2 m/s So, the boat
was traveling at 2 m/s Now you try What is the
speed of a car that is traveling 150 miles in 3
hours?
22
Answer
  • Step 1 What are the facts in the problem?
  • A car is traveling 150 miles in 3 hours.
  • Step 2 What is the formula to solve the
    problem? Speed Distance/Time
  • Step 3 Solve the problem.
  • Speed 150 miles 3 hours
  • Speed 50 miles/hr.
  • So, the car is traveling 50 miles/hr.

23
Acceleration
  • Acceleration is the rate at which velocity
    changes.
  • Acceleration can result from a change in speed
    (increase or decrease), a change in direction
    (back, forth, up, down left, right), or changes
    in both.

24
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28
  • The pitcher throws. The ball speeds toward the
    batter. Off the bat it goes. Its going, going,
    gone! A home run!
  • Before landing, the ball went through several
    changes in motion. It sped up in the pitchers
    hand, and lost speed as it traveled toward the
    batter. The ball stopped when it hit the bat,
    changed direction, sped up again, and eventually
    slowed down. Most examples of motion involve
    similar changes. In fact, rarely does any
    objects motion stay the same for very long.

29
Understanding Acceleration
  • 1. As the ball falls from the girls hand, how
    does its speed change?

2. What happens to the speed of the ball as it
rises from the ground back to her hand?
3. At what point does the ball have zero
velocity? When it stops and has no direction.
4. How does the velocity of the ball change when
it bounces on the floor?
30
You can feel acceleration!
If youre moving at 500mph east without
turbulence, there is no acceleration.
But if the plane hits an air pocket and drops 500
feet in 2 seconds, there is a large change in
acceleration and you will feel that!
It does not matter whether you speed up or slow
down it is still considered a change in
acceleration.
31
In science, acceleration refers to increasing
speed, decreasing speed, or changing direction.
  • A car that begins to move from a stopped position
    or speeds up to pass another car is accelerating.
  • A car decelerates when it stops at a red light. A
    water skier decelerates when the boat stops
    pulling.
  • A softball accelerates when it changes direction
    as it is hit.

32
Calculating Acceleration
  • Acceleration Change in velocity
  • Total time

SoAcceleration (Final speed Initial speed)

Time
33
Calculating Acceleration
  • As a roller-coaster car starts down a slope, its
    speed is 4 m/s. But 3 seconds later, at the
    bottom, its speed is 22 m/s. What is its average
    acceleration?

What information have you been given? Initial
speed 4 m/s Final Speed 22 m/s Time 3 s
34
Calculating Acceleration
What quantity are you trying to calculate? The
average acceleration of the roller-coaster
car. What formula contains the given quantities
and the unknown quantity? Acceleration (Final
speed Initial speed)/Time Perform the
calculation. Acceleration (22 m/s 4 m/s)/3
s 18 m/s/3 s Acceleration 6 m/s2 The
roller-coaster cars average acceleration is 6
m/s2.
35
Graphing acceleration
S P E E D
Object accele-rates
Object decelerates
Object moves at constant speed
T i m e
36
Now You TryA roller coasters velocity at
the top of the hill is 10 m/s. Two seconds later
it reaches the bottom of the hill with a velocity
of 26 m/s. What is the acceleration of the
coaster?
37
The slanted, straight line on this
speed-versus-time graph tells you that the
cyclist is accelerating at a constant rate. The
slope of a speed-versus-time graph tells you the
objects acceleration. Predicting How would the
slope of the graph change if the cyclist were
accelerating at a greater rate? At a lesser rate?
38
Since the slope is increasing, you can conclude
that the speed is also increasing. You are
accelerating.
Distance-Versus-Time Graph The curved line on
this distance-versus-time graph tells you that
the cyclist is accelerating.
39
Acceleration Problems
  • A roller coaster is moving at 25 m/s at the
    bottom of a hill. Three seconds later it reaches
    the top of the hill moving at 10 m/s. What was
    the acceleration of the coaster?
  • Initial Speed 25 m/s
  • Final Speed 10 m/s
  • Time 3 seconds
  • Remember (final speed initial speed) time is
    acceleration.
  • (10 m/s 25 m/s) 3 s -15 m/s 3 s -5
    m/s2
  • This roller coaster is decelerating.

40
  • A cars velocity changes from 0 m/s to 30 m/s in
    10 seconds. Calculate acceleration.
  • Final speed 30 m/s
  • Initial speed 0 m/s
  • Time 10 s
  • Remember (final speed initial speed) time is
    acceleration.
  • (30 m/s 0 m/s) 10 s 30 m/s 10 s 3 m/s2

41
  • A satellites original velocity is 10,000 m/s.
    After 60 seconds it s going 5,000 m/s. What is
    the acceleration?
  • Remember (final speed initial speed) time is
    acceleration.
  • Final speed (velocity) 5000 m/s
  • Initial speed (velocity) 10,000 m/s
  • Time 60 seconds
  • (5000 m/s 10,000 m/s) 60 s -5000 m/s 60 s
  • -83.33
    m/s2
  • This satellite is decelerating.

42
  • If a speeding train hits the brakes and it takes
    the train 39 seconds to go from 54.8 m/s to 12
    m/s what is the acceleration?
  • Remember (final speed initial speed) time is
    acceleration.
  • Final speed 12 m/s
  • Initial speed 54.8 m/s
  • Time 39 s
  • 12 m/s 54.8 m/s 39 s -42.8 m/s 39 s
  • -1.097
    m/s2
  • This train is decelerating.
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