Download FORCES MOTION and ENERGY Teacher Notes

January 20, 2016
Essential Questions:

1. Why is choosing a reference point
important when describing your motion?

2. How is motion related to energy?

An object is considered to be in motion
when it’s distance changes in
relationship to another object.

Right now, are you in motion? How do
you know?

An object is considered to be in motion
IF it changes position relative to its
reference point.

So now that you are thinking about your
reference point, are you currently in
motion? How do you know? What is your
reference point?

Hmmm….ever heard of Kinetic Energy and
Potential Energy?

What do each of these mean and how are
they related to motion?

So if you are in motion are you losing or gaining
energy?

(What does the Law of Conservation of Energy
say??)
Essential Questions:

1. What is the relationship between time,
speed, and distance?

2. How are these (time, speed, and
distance) related to motion?

When you talk about motion, you have
to consider the distance traveled as well
as the speed you are traveling and the
time involved.

So, if you are in motion over a distance
of 75 km and it takes you 2 hours to
arrive, what is your speed?

Speed = Distance
Time
Example: 75km
2hrs
Answer = 37.5km/hr.
Problem: You are going to grandma’s
house for the holiday. You are traveling
at a speed of 50mph going southwest
and grandma lives 238 miles away. How
long will it take you to reach grandma’s
house?

What this means is that if one goes up
the other goes down by the same
proportion 

So...to find Time this is your formula:
Time = Distance
Speed
Time = Distance
Speed
Time = 238 miles
50mph
Answer = 4.76 hours
Well….you would just simply multiply your
Speed x the Time it took you to reach your
destination, and you will get your answer 
Problem: Your school bus is traveling at a
speed of 35mph and you are in the moving
bus (no stop lights and no stop signs) for
18 minutes. How far did you travel?
Distance
=
Speed x Time
(35mph) (18minutes)
OH NO>>>
my units don’t match! 
What am I going to do to find my answer?

35 mph means you went 35 miles in 1
hour, and you traveled for 18 minutes so
how many miles did you go in 18
minutes….(remember: 60 minutes = 1
hour!!) mph stands for miles/hour so…
(35miles) x (18minutes) x (1hour)
1 hour
60 minutes
The answer is 10.5 miles 
Now try another one for distance….
PROBLEM: The jet plane you are on is
leaving Greensboro traveling south to
Charlotte. The plane is traveling at a
speed of 375mph and you arrive in
Charlotte in 17 minutes. How long did it
take you to get to Charlotte by plane?
Remember the formula …
Distance = Speed x Time
375mph x 17minutes x (1hour)
(60 minutes)
Remember: There a 60 minutes in 1 hour
and your speed is in mph (miles/hour)!!
To find the velocity, use the same formula
as you did to find the speed….
Speed = Distance
Time
Then tell what direction you are traveling
(N,S,E,W,SE, SW, NE, NW) and you have
your velocity!!!
1. Why do you need a reference point to
know if an object is moving?
 2. What is the difference between the
speed of an object and its velocity?
 3. A bamboo plant grows 15cm in 4
hours. At what average speed did the
plant grow?
 4. If you went 15mph North and then
turned around and went 15mph south,
what would you say was your velocity?

5. How much time will it take a car to
travel 500 miles, if it is going at the
average speed of 65mph?
 6. If an object is traveling south at a
constant velocity of 35mph, what is its
average speed?
 7. If a car is moving at 55mph and it
takes 5 hours to reach its destination,
what distance did it travel?

8. What is the velocity of a car traveling
west for 5 hours and covering a distance
of 375 miles?
 9. If Earth’s plates move at a rate of 5mm
in 100 days, what is its speed in mm/day?
 What is its speed in mm/year?
 10 What would cause an object to
change its course of direction?

Acceleration is the rate at which velocity
changes.
 In science, acceleration refers to an
increase in speed, a decrease in speed
(deceleration), or a change in direction .
 IMPORTANT NOTE: IF an object is traveling
a constant speed, it can still be
accelerating IF IT IS CHANGING
DIRECTION!

Acceleration = Final velocity – initial velocity
time

Problem: A rollercoaster picks up speed
as it rolls down a slope. As it starts down
the slope, its speed is 4m/s. But 3 seconds
later, at the bottom of the slope, its
speed is 22m/s. What is the average
acceleration of the rollercoaster?
Acceleration = Final velocity – Initial velocity
time
Acceleration = 22m/s – 4m/s
3s
Acceleration = 18m/s
3s
= 6m/s²
Question: Why is it m/s² ?

1. A car advertisement states that a
certain care can accelerate from 0 to
90km/hr in 9 seconds. Find the car’s
average acceleration.

2. An eagle accelerates from 15m/s to
22m/s in 4 seconds. What is the eagle’s
average acceleration?
Time (hours)
Distance (km)
http://www.projectsharetexas.org/node/4117
http://www.physicsclassroom.com/class/1DKin/Lesson-3/The-Meaning-of-Shape-for-a-p-t-Graph
http://camillasenior.homestead.com/motion_graphs.pdf

A horse is trotting around a large circular
path, maintaining a constant speed of of
5m/s. Is the horse accelerating? Why or
why not? Explain your answer.
1. How does the steepness of a ramp
affect how fast an object can travel?
 2. How does the acceleration of an
object depend upon its mass and the
force applied?
 3. How does friction affect an object’s
motion and speed?
 4. Do the shoes I wear on the basketball
court affect my speed? Why/Why not?






Force is the push or pull on an object.
Forces are described not only as how strong
they are, but also by the direction in which
they act.
When 2 forces act in the same direction, add
them together.
When 2 forces act in opposite directions,
subtract them from each other.
If one force is greater than the other, the
overall (net) force is in the direction of the
greater one.





The overall, combined force, is called the net
force.
An unbalanced force on an object will change
the object’s direction. (which will result in
acceleration or deceleration)
Balanced forces will NOT change the object’s
direction. (constant force or net force = zero!)
For an object to be in motion, a force must act
upon the object.
All objects tend to resist change to motion. This
resistance to change in motion is called inertia.
An object at rest will remain at rest.
 An object in motion will remain in motion.
 An object that is moving at a constant
speed will remain at that constant speed
unless acted upon by an unbalanced
force.

The amount of inertia an object
has depends upon its mass.
Therefore, mass is the measure of
an object’s inertia.
 Remember: Mass is the amount
of matter in an object.
 Remember: The SI unit for mass is
kilogram (kg)

Force = Mass x Acceleration
KNOW THAT THIS IS NEWTON’S SECOND
LAW OF MOTION!!

Force = kg x m/s².
The unit for Force which is kg x m/s² will be
expressed in Newtons.
Remember: If your units for mass or acceleration
do not match you must convert them!!

Acceleration = Force
Mass

Increase acceleration by either decreasing
the mass or increasing the force.

Decrease acceleration by either increasing
the mass or decreasing the force.
1. Two children are fighting over a toy and
pulling from opposite sides. Which child will
win? Why is this?
 2. Draw a diagram to show balanced
forces. Explain your diagram to your
partner.
 3. A 52kg water skier is being pulled by a
speedboat. The forces causes her to
accelerate at 2m/s². Calculate the force
that causes this acceleration.

4. What 3 quantities are related to Newton’s
laws of motion? How are they related?
 5. Suppose you double the force acting on
an object. How could you change the mass,
to keep the object from accelerating?
 6. If you push a dime, a penny, a nickel,
and a quarter off your desk at the same
time, which one would reach the ground
first? Why?(HINT: Try it and see what
happens!!)

WHAT ARE THE 2 FORCES THAT
USUALLY AFFECT MOTION?

1. FRICTION – The strength of the force of
friction depends upon two factors:
1. the type of surfaces involved.
2. how hard the surfaces push together.
2. GRAVITY – On earth, all objects fall at the
same rate of 9.8m/s2.
 HINT: If acceleration is not given and you are
asked to calculate force, then use your
gravity number, which is 9.8m/s2.

Universal law of Gravitation

The force of gravity acts between all
objects in the universe.
KNOW THIS LAW
WHAT IS THE NUMBER THAT REPRESENTS THIS
LAW?
Remember: Weight = Mass x Acceleration

If one object exerts a force on another
object, then the second object will exert
a force of equal strength in the opposite
direction on the first object.
KEY POINTS:
equal but opposite
action vs. reaction

Why don’t action and reaction forces
cancel each other?

What did Newton mean by “QUANTITY
OF MOTION”?
What is Momentum?

The quantity of motion, represented by the
formula:
Momentum = Mass X Velocity

The more momentum an object has, the
harder it is to stop the object motion.

You can change the momentum by
changing its mass or its velocity.

Satellites orbit around the Earth
continually falling toward the earth, BUT
the Earth is curved, so satellites travel
around the Earth. (Remember: A change
in motion causes acceleration!)

Earth’s surface curves away from the
satellite at the same rate the satellite is
falling toward the Earth due to gravity.
1. What is the vocabulary word describing
the push or pull on an object?
 2. What is the vocabulary word that
describes speed divided by time?
 3. What is the vocabulary word that
describes speed divided by acceleration?
 4. If a car is traveling north for 475 miles at a
average speed of 50mph how much time
will it take to reach its destination?

5. If two basketball players collide and one
falls down, what kind of force is
represented?
 6. If an object is traveling at a constant rate
of 10m/s, what is its acceleration?
 7. How far does a train traveling south at
75mph if it takes 4 hours to reach it
destination?
 8. Why do bridges, overpasses, and
wheelchair ramps have rough surfaces?

9. Why does an object sliding across a
smooth flat surface eventually stop?
 10. What type of force causes an object
to change its direction or motion?
 11. If the team score is tied (no one is
winning) what is the net force?
 12. What is the velocity of a car traveling
southwest for 6.5 hours and covering 400
miles?

13. What is the acceleration of ball traveling
for 4 seconds whose initial speed is 16m/s and
its final speed is 28m/s?
 14. What is a race car’s acceleration from rest
to 65m/s in 5 seconds?
 15. What is the best vocabulary word you
should use to describe a force when equal
and opposite forces are acting on an object?
 16. What is the best vocabulary word you
should use when describing resulting forces?

Buoyancy is…

Defined as the force that acts in
an upward direction (the force
opposite gravity!!).

Newton’s 3rd Law states that for
every reaction you have an
equal but opposite reaction.

Buoyancy is the equal to,
but the opposite reaction of
gravity!!

Is equal to the weight of the fluid
displaced by the object. (the reason a
boat floats!!)

Is known as Archimedes Principle.
How can you use the density of an object
to determine if the object will sink or float?
 Density = mass/volume


See page M 95 (NC Integrated Science –
blue book)for a density comparison chart
of various substances.

Question: The density of lead is 11.3g/cm³.
Will lead float or sink in water? How do you know?
Pressure = Force
Area
=
N
m²
= 1 Pascal
(Remember your math: Area = l x w)
 How
could you increase the force?
 How
could you increase the area?
1.
So if air pressure exists, then why don’t you
feel the pressure? (or do you???)
2.
When you climb a mountain (increase
elevation) what happens to the air
pressure? What happens to the
temperature?
3.
As you dive deeper into the ocean, what
happens to the air pressure?

Use Pascal’s Principle which states, “ When
force is applied to a confined fluid, an
increase in pressure is transmitted equally
to all parts of the fluid.

Fire trucks use Pascal’s Principle to put out
fires in tall buildings.

Your heart uses Pascal’s Principle to pump
your blood.
states, “ a pressure exerted by a moving
stream of fluid is less than the surrounding
fluid”.
 Remember: Air consists of fluids (such as water
vapor), so if the wind under an airplane is
moving faster, than it is moving on the top of
the plane, the plane will fly.


So…Your heart is beating
because of Bernoulli’s
Principle!!
In order for you to show evidence of work on
an object, the object must move as the result
of your force. Question: Are you working right
now… this very instant? How do you know?
Hint: Is your pencil moving as you take notes? Is
there evidence of your note taking in your
science journal? How much work are you
doing each day in science class
REMEMBER: Daily grades & Projects in
Karen Storey’s Science Class =
50% of your total grade!!
TO BE TRULY WORKING, THE FORCE YOU
EXERT MUST BE IN THE SAME DIRECTION AS
THE OBJECT’S MOTION!!
 What this means in every day language is
this: Are you increasing in your productivity
(growing)? If you are, then you are working.

 OK…RIGHT NOW Give 3 examples of
evidence of Work, using REAL WORLD
EXAMPLES!!

1. When you lift your books off your desk,
are you working? Why/Why Not?
 2. When you ride the school bus to school, is
work involved? Why/Why not?
 3. How can using technology help you in
your work?
 4. Does having a pencil in class each day
help you in your work? Why/Why not?
 5. Would a pencil be considered
technology? Why/Why not?

Work = Force x Distance
(KNOW : The SI Unit for work is Joule.

Joule is a measure of the net amount of Kinetic
Energy.
 So how can you prove each day to your
teacher and to your parents that you are truly
working in science class? (Give 3 ways!!)
 How can using the technology (tools/machines)
you need in science class and at home make
your work easier and help you prove to your
teacher and to your parents that you are
working every day??
1. Determine the amount of work you must do
to lift a 600g can of soup 15 cm.
 2. If you want to increase your amount of
work evidence, what do you need to do?
 3. A hydraulic lift raises a 12,000N car 2 m.
How much work is being done on this car?
 4. If the mechanic working on your car (see
above) uses a hydraulic lift, will the use of this
technology be included in your repair bill?
Why/Why not?

5. Suppose Karen Storey is your coach and
Karen (Mrs. Storey) wants you to show
evidence of your work ethics each day.
What are you going to do each day to show
Karen Storey that you are serious about
improving your overall performance?
 6. You want to improve your bowling score.
(Remember: Those working in science class
get to go bowling the end of this semester!!)
If you change your center of mass, could
you change your bowling score? Why/Why
not?


Work = Force x Distance

Power = Force x Distance
Time

Work = Transfer of Energy

Power = Rate at which energy is transferred.

A machine helps make your work easier by
changing the amount of force you exert, or
by changing the distance over which the
force is exerted, or by changing the
direction in which you exert the force.
Is a bowling ball a machine? Why/Why not?
 Is a bowling ball technology? Why/Why not?


Are machines technology? Why/Why not?
Net performance = net efficiency
 If your output force is greater than your input
force you increase your overall
performance. Machines/technology can
help you increase your output force!!
 Think about this: You are a landscaper
(Landscaping is your career) and a dump
truck has just delivered a ton of mulch 10
meters from where it belongs. What could
you do to make your job of moving the
mulch easier?


NOTE: If a machine (technology) allows you
to use less force to do the same amount of
work you must increase your distance.

QUESTION: What type of technology would
allow you to exert a smaller force over a
longer distance? (this would decrease your
work input but increase your work output so
your net work would actually increase!)
Output work
Input work
x 100 %
Remember: Efficiency = performance,
and performance is always out of 100%.
Therefore 100% = perfect efficiency which
equals perfect performance.

If you do 1,500J of work using a hammer,
and the hammer does 825J of work on a
nail, what is the efficiency (the
performance measure) of the hammer?
Efficiency = Output work
Input work
x 100 %
= 825J
x 100 %
1500J
IMPORTANT NOTE: Mathematically speaking
YOU should never be greater than 100%!
Question: What could you do to increase the
efficiency of the hammer? Will this change
increase your work load? Why/Why not?
1. Inclined planes
 2. Wedges
 3. Screws
 4. Levers
 5. Wheels & Axles
 6. Pulleys
Question: Do you see
any of these in the
picture?


are also called complex machines,
because they are a combination of 2 or
more simple machines.

A mechanical pencil sharpener is a good
example of a compound machine.

Question: At WSPA (Winston Salem
Preparatory Academy) do we have any
wheelchair ramps? Should we? Why/Why
not?





1. Suppose you need to move a huge rock.
How would a lever help you?
2. How can changing a fulcrum increase or
decrease your mechanical advantage?
`Give an example to explain your answer.
3. How does a pulley help to change the
direction of the force?
4. How can you increase the mechanical
advantage of a pulley system?
5. What kind of a lever is the “flip top” on a soda
can? Explain your answer using a diagram.
For standardized practice test questions
about Force, Work, & Motion visit:

http://glencoe.mcgrawhill.com/sites/0078768349/student_view0/unit
2/chapter5/standardized_test_practice.html
For some additional questions on Weather
and the Atmosphere, visit the website
below.

http://glencoe.mcgrawhill.com/sites/0078768349/student_view0/u
nit3/chapter12/standardized_test_practice.
html