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Notes
Application
Balanced means to equal or be in
equilibrium.
The prefix “Un” in front of a word means
“not”. Therefore unbalanced refers to
something that is not balanced or equal.
Label each of the images to the right as
either balanced or unbalanced.
A force is either a push or pull. Unbalanced
forces on objects cause a change in motion.
Change in motion occurs in the direction
where the largest magnitude is present.
Does this image represent a balanced or
unbalanced force? Explain your answer.
The magnitude (or size) of the force
determines the net force (total force).
Arrows are used to show the magnitude of a
force. Large magnitudes have larger arrows.
Look at one of the boxes above to show you
how to draw our arrows.
Illustrate a box moving North East by
placing ALL of the following magnitudes
on the box to the right.
20 N, 10 N, 60 N, 60 N
Make sure to draw arrows that accurately
represent the magnitude.
One can calculate the net force (total force)
by simple addition and subtraction.
There can be more than one force acting on
an object from one direction. In this case,
the forces must be added.
However the forces acting on an object from
different direction must be subtracted.
Use your QR scanner to watch the video.
To fully understand motion and unbalanced
forces, one must understand speed, velocity,
and acceleration.
Based on this video, which of the following
statements is true?
A. To determine the force required to push a
car, the force of each kid must be added.
B. To determine the force required to push a
car, the force of each kid must be subtracted.
C. The force of the car is greater than the
force of the students.
D. The force of the car is equal to the force of
the students.
When driving in a car you can determine the
speed using the spedometer. The spedometer
shows the miles per hour (mi/hr).
Speed refers to "how fast an object is
moving." Speed can be thought of as the
rate at which an object covers distance.
Based on this information, which of the
following would be the formula for speed?
(HINT: focus on the words in bold above).
A fast-moving object has a high speed and
covers a relatively large distance in a short
amount of time.
A. Distance
Time
Contrast this to a slow-moving object that
has a low speed; it covers a relatively small
amount of distance in the same amount of
time.
B.
Distance
Force
C.
Time
Distance
D.
Time
Force
An object with no movement at all has a zero
speed. http://www.physicsclassroom.com/class/1DKin/Lesson1/Speed-and-Velocity
Instantaneous Speed - the speed at any
given instant in time.
Average Speed - the average of allinstantaneous speeds; found simply by a
distance/time ratio.
Practice determining the speed of each of
the following.
1. A car travels 300 km in 6 hours.
2. What is the speed of a jet plane that flies
7200 km in 9 hours (in km/hr)?
3. What is the average speed of a walker who
walks 500 m in 400 seconds?
Instant speed and average speed can be
determined using a graph. Look at the graph
below.
What is the speed of both runners at 4
seconds?
Who covered more distance in 4
seconds?
Distance vs Time graphs provide a great deal
of information. Look at the graph below.
What time did the fastest runner finish
the race?
Point “A” is the starting point. Notice how
the driver start out at a constant rate.
Then, the graph shows a flat horizontal line.
This is the time at rest. The time continues
to run but there is no distance covered.
Circle the runner that stopped for a rest.
How long did he stop?
Finally the graph shows a downward slope.
Here the driver is returning back to the
starting point “A”.
Draw a graph below that shows a student
walking from home to school. She starts
walking at a steady pace. Then she stops to
talk to a friend. Finally she realizes that she
is running late and starts to run to school.
Practice sheet should be provided to students at this point.
Velocity refers to "the rate at which an
object changes its position."
Imagine a person moving rapidly - one step
forward and one step back - always returning
to the original starting position. While this
might result in a frenzy of activity, it would
result in a zero velocity.
Because the person always returns to the
original position, the motion would never
result in a change in position. Since velocity is
defined as the rate at which the position
changes, this motion results in zero velocity.
If a person in motion wishes to maximize
their velocity, then that person must make
every effort to maximize the amount that
they are displaced from their original
position.
The following statements are all false.
Underline the section that makes them
false. Correct each section to make the
sentence true.
1. Balanced force causes a change in
motion.
2. Speed is the rate at which an object
changes its position.
3. Velocity can be calculated by dividing
distance over time.
4. Movement that results in returning to the
original starting position has velocity.
What is the main difference between
speed and velocity?
It would not be enough to say that an object
has a velocity of 55 mi/hr. One must include
direction information in order to fully describe
the velocity of the object. For instance, you
must describe an object's velocity as being 55
mi/hr, east. This is one of the essential
differences between speed and velocity.
Acceleration is defined as the rate at which
an object changes its velocity. An object is
accelerating if it is changing its velocity.
Sports announcers will occasionally say that a
person is accelerating if he/she is moving
fast. Yet acceleration has nothing to do with
going fast. A person can be moving very fast
and still not be accelerating. Acceleration has
to do with changing how fast an object is
moving. If an object is not changing its
velocity, then the object is not accelerating.
An object with a constant acceleration should
not be confused with an object with a
constant velocity. Don't be fooled! If an object
is changing its velocity -whether by a
constant amount or a varying amount - then
it is an accelerating object. And an object with
a constant velocity is not accelerating.
Define the following words in your own
terms.
1. Speed
2. Velocity
3. Acceleration
4. Force
An object is traveling at 10 m/s as it turns.
Which of the following statements describes
the object’s motion?
The object is accelerating and has
constant speed.
A
http://www.physicsclassroom.com/class/1DKin/Lesson1/Acceleration
Use QR scanner to watch the
video.
The object is accelerating and has
constant velocity.
B
The object is not accelerating, but has
constant speed.
C
The object is not accelerating, but has
constant velocity.
After a student investigated the effects of
unbalanced forces on an object, which
statement below should they include in
their conclusion?
D
The following statement summarizes the
relationship between force and motion.
If the forces acting on an object are balanced
and the object is in motion, then it will
continue in motion with the same velocity.
Forces do not cause motion. Forces cause
accelerations.
F
Unbalanced forces cause the net force of
an object to be zero.
G
Unbalanced forces cause an object to
maintain its state of motion.
H
Unbalanced forces cause an object to
start moving, stop moving, or change
directions.
Unbalanced forces cause an object to
maintain the same speed and the same
direction.
Provide students the opportunity to practice comparing using a double T chart.
J