Title: Average Speed
1Average Speed
- Mrs. Martinez
- Sixth Grade
2Welcoming Work
- Review
- What is Force?
- What is a balanced force? Describe by using
arrows to draw a diagram. - What is an unbalanced force? Describe by using
arrows to draw a diagram. - Getting your brain gears turning.
- What is a distance-time graph?
- What is Motion?
- What is the connection between Speed, Distance,
and Time?
3Forces
- A force is a push or pull that one body exerts on
another. A force can cause the motion of an
object to change. There are two types of forces - Balanced force one in which the net force is
zero. - Unbalanced force one in which the net force has
a numerical value.
4Forces
Balanced Force Net force 0
- 1 force
1 force
Unbalanced Force Net force -1
1 force
- 2 force
Unbalanced Force Net force 2
1 force
1 force
5Turn and Talk
6What Is Motion?
- Motion is when an object changes place or
position. To properly describe motion, you need
to use the following - Start and end position?
- Movement relative to what?
- How far did it go?
- In what direction did it go?
7Motion Re-Cap
- When an object changes its position, motion has
occurred. - Distance- How far an object has moved.
- Displacement- How far an object has moved in
relation to its starting point. - Consider direction
- Example Two runners travel along the same
straight path in a straight line for 500 meters.
At the end of the run their distances are the
same but their displacements are different. How
can this be so?
8SPEED
Describes how fast an object is moving.
9What Is Speed?
- Speed is the distance an object travels in a
certain amount of time (relationship of all 3) - To calculate speed, you use the following
formula - Speed (s) Distance(d)
- Time (t)
10Speed- Distance an object travels per unit of
time
- Relationships between speed, distance, and time
- Speed Distance/ Time d/ t
- Constant Speed- speed does not change over time
- Average Speed- speed of motion when speed is
changing - Avg Speed Total Distance/ Total Time
- Instantaneous Speed- speed at any given moment in
time (speedometer)
11The 3 formulas for Speed, Time Distance Using
your W/B write them down without using your
notes.
Solving for Speed
Solving for Time
Solving for Distance
Remember them from this triangle
12Dont Remember huh? Well lets refresh that
memory!
- http//www.youtube.com/watch?v9x7hP5LM1UE
13Turn and Talk What is the Relationship between
speed, distance and time?
- Speed is the distance an object travels in a
certain amount of time
14Average Speed
Total distance
Average Speed
Total time
15WB Time!
- Lets check out your knowledge! Without using
your notes answer - What is the formula for finding speed?
- What is the formula for finding time, using
distance and speed? - What is the formula for finding distance using
speed and time?
16Try this
- Mrs. Martinez walks home from her sisters house
everyday. It takes her 4 minutes and her house is
240 meters away.What is her average speed? - 240 meters/ 4 minutes
- 60 meters per minute.
17Example Question 1
- Jane drives at an average speed of 45 mph on a
journey of 135 miles.How long does the journey
take? - To find a time, we need to divide distance by
speed. - 135 miles 45 mph 3 hours
18Example Question 2
- Chris cycles at an average speed of 8 mph.If he
cycles for 6½ hours, how far does he travel? - To find a distance, we need to multiply speed by
time. - 8 mph 6.5 hours 52 miles
19Example Question 3
- Nikki has to travel a total of 351 miles. She
travels the first 216 miles in 4 hours.(a) What
is her average speed for the first part of the
journey? - To find average speed, we need to divide
distance by time. - 216 miles 4 hours 54 mph
20- Her average speed is the same for the whole of
her journey. - (b) How long does the whole journey take?
- To find time, we need to divide distance by
speed. - 351 miles 54 mph 6.5 hours
21Reminder How to change minutes into a decimal
15 mins 025 hour So 3 hours 15 mins 325
hours
30 mins 05 hour So 7 hours 30 mins 75
hours
45 mins 075 hour So 2 hours 45 mins 275
hours
22First work it out on your paper then show me on
your WB. A windsurfer travelled 28 km in 1 hour
45 mins. Calculate his speed.
Speed
1 hour 45 mins
16 km/h
Answer His speed was 16 km / hour
23A salesman travelled at an average speed of 50
km/h for 2 hours 30 mins. How far did he travel?
Distance
Speed x Time
2 hour 30 mins
50 x 25
125 km
Answer He travelled 125 km
24A train travelled 555 miles at an average speed
of 60 mph. How long did the journey take?
Time
925 hours
9 hours 15 mins
Answer It took 9 hours 15 minutes
25Speed Problem
- Suppose you ran 2 km in 10 min. What is your
speed? - S 2 km 0.2 km/min
- 10 min
26Ways To Calculate Speed
- Constant speed is when you are traveling at the
same rate of speed, such as 55 mph constantly on
a highway. - Average speed is taking the total distance
traveled, and dividing by the total time it
takes. Used for calculations that involve
changing speed. - Instantaneous speed is the speed at any one given
point in time.
27Sooo What is the formula for speed?
- http//www.youtube.com/watch?featureendscreenvK
_kzgW_OYX0NR1
28Practice Question 1
- Jim travels 45 miles at 15 mph.How long does it
take him?
29 30Practice Question 2
- Jemimah walks at 4 mph for 2½ hours.How far
does she walk? - She walked 10 miles.
- 4 mph x 2.5 hrs 10 miles
31Practice Question 3
- Jenny drives at a constant speed. In the first
three hours she travels 81 miles.How far will
she have travelled after 5 hours? - She will travel 135 miles
- 27 mph for 5 hrs 135 miles
32Graphing Average Speed
- Using a Distance-Time Graph
33Graphing Motion
- Graph distance on the y-axis and time on the
x-axis
- Slope rise distance speed
- run time
34Graphing Speed
- Speed is usually graphed using a line graph, and
it depicts the distance and time. - Time is the independent variable, and thus is
ALWAYS on the x-axis. - Distance is the dependent variable, and is ALWAYS
on the y-axis.
35Average Speed
What is the AVERAGE speed of the bass boat
depicted in the graph?
Average Speed 125 meters 15.6 m/s
8 seconds
36Instantaneous Speed
What is the instantaneous speed of the bass boat
at t7 seconds?
Instantaneous Speed 85 meters 12.1 m/s
7 seconds
37Speed Graphs
- In what time period is the bass boat speeding up?
- In what time period is the bass boat slowing
down? - When is the speed NOT changing?
38Distance - Time Graph
- If something is not moving, a horizontal line is
drawn. - If something starts out slow and then speeds up,
its change in speed can look like this.
39Learning Checkpoint
- This graph shows several stages of motion
- Stage 1 100 m in 10 s
- Stage 2 50 m in 10 s
- Stage 3 150 m in 20 s
- Calculate the speed as indicated by each of the
colors. - Calculate the average speed.
- What is the total distance?
- What is the displacement?
40Solution
Stage 1 S d/ t 100 m/ 10 s 10 m/s Stage 2
S d/t 50 m/ 10 s 5 m/s Stage 3 S d/t 150 m/
20 s 7.5 m/s Avg Speed Tot d/ Tot t 300 m/ 40
s 7.5 m/s Distance 300 meters Displacement 0
meters
413) At a daily basis, you rotate between classes.
Draw a distance vs time graph illustrating the
distance you travel during class rotations here
at school
42Video Recap
- http//www.youtube.com/watch?vSpz8WfmREDMNR1fe
aturefvwp
43Average Speed Recap
- http//www.youtube.com/watch?vWxCgVNqfub8
44Velocity
The speed of an object in a certain direction.
45Velocity
- Velocity is the speed of an object, but the
direction is also included. It is calculated the
same as speed, but you must include a direction
in your answer. - Example the bass boat was moving 12 mph toward
the north.
46d
Velocity
V
t
speed of an object in a certain direction.
V velocity (meters/second) d distance
(meters) t time (seconds)
47Velocity
speed of an object in a certain direction.
0
seconds
3
1
2
48Velocity
- The speed and direction of an objects motion.
- 88 km / hr southwest
49Speed? Velocity?
B
Total time 4 seconds
20 meters
12 meters
16 meters
A
50Acceleration
- Acceleration is the rate of change of velocity.
A change in velocity can be either a change in
speed, or direction, or both. - Deceleration is when acceleration has a negative
value.
51Acceleration
- The formula for calculating acceleration is
- Acceleration (a) final velocity (vf) initial
velocity (vi) - time
(sec) - The unit for velocity, in this case, is
- m/s/s OR m/s2
52Acceleration Math Problem
- A jet starts at rest at the end of a runway and
reaches a speed of 80 m/s in 20 s. What is its
acceleration? - a 80 m/s - 0 m/s 4 m/s2
- 20 s
53Acceleration Math Problem
- A skateboarder is moving in a straight line at a
speed of 3 m/s and comes to a stop in 2 sec.
What is his acceleration? - a 0 m/s - 3 m/s -1.5 m/s2
- 2 m/s
54Inertia
- Inertia is the tendency of an object to resist
any change in motion. Put in another way, if an
object is moving, it will keep moving until an
outside force acts on it. - Inertia is related to mass the greater the mass
of an object, the greater its inertia.
55Newtons 1st Law of Motion
- Newtons 1st Law is also known as the law of
inertia. It says - An object in motion will stay in motion, and an
object at rest will stay at rest, unless acted
upon by an outside force. - Example if you are approaching a fence on a
running horse, and the horse suddenly stops, you
will keep going forward over the horses head
unless you are wearing a seatbelt! (I dont care
who you are thats funny!)
56Inertia
- What does a seat belt do for us,
- in terms of inertia?
- -it helps us OVERCOME inertia!
57http//www.cimt.plymouth.ac.uk/projects/mepres/boo
k8/bk8i18/bk8_18i2.htm http//baldragon.ea.dunde
ecity.sch.uk/Departments/Physics/Movementint1/Aver
agespeedweb.htm