UNIT 2: PHYSICS
Chapter 1: Describing Motion
NAME:____________________
MAJOR CONCEPT #1: Ch.1 - One-dimensional motion
I CAN
…
o
Distinguish between scalar and vector quantities (distance vs displacement,
speed vs velocity).
o
Define and calculate velocity and acceleration using the formulas:
o
Compare and perform calculations involving uniform motion and uniform
accelerated motion, using the formulas:
o
Analyze position-time and velocity-time graphs to explain the relationships
between displacement, velocity and acceleration.
o
Apply Newton’s first law of motion (Law of Inertia) by explaining an objects
state at rest or uniform motion.
o
Apply Newton’s second of law of motion to relate force, mass and motion by
Explaining how an unbalanced force causes change in motion .
MAJOR CONCEPT #2: Ch.2 - Momentum
I CAN
…
o
Define and calculate momentum in one-dimensional collisions using .
o
Define change in momentum as impulse, calculate impulse
and relate impulse to Newton’s second law of motion using .
o
Apply the concept of impulse to explain how safety devices work.
o
Apply Newton’s third law of motion to explain the interaction between two
objects in a collision.
1 Vector Quantity:
-a quantity consisting of magnitude and direction.
Learning Objectives:
1) I can distinguish between scalar & vector quantities (distance vs displacement, speed vs velocity)
2) Define velocity as v = /
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Gizmo "d vs t"
UNIFORM MOTION:
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7 HOMEWORK: p.173 #2-4
G - what info is given?
R - what is required/requested?
A - analyze
(what formula, manipulate formula, sig digs, unit conversion)S - solve by substituting into the formula
P - paraphrase your answer in a sentence
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Learning Objectives:
1) I can distinguish between scalar and vector quantities, including distance and displacement, speed and velocity.
2) I can define velocity and acceleration as v = ∆d / ∆t and a = ∆v / ∆t , respectively.
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(p.179 in Textbook)
Using Scale Diagrams
Distance vs Position
When calculating the position of an object it is easier if you use
sign
5 (p.179 & 180 in Textbook)
Displacement
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9
17. a) Determine the displacement from the Scalzo Creek crossing to the John Creek crossing and from the John Creek crossing to base camp.
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Name: ______________________________________ Date: ________________________
Student Exploration: Distance-Time Graphs
Vocabulary: speed, y-intercept
Prior Knowledge Questions (Do these BEFORE using the Gizmo.) Max ran 50 meters in 10 seconds. Molly ran 30 meters in 5 seconds.
1. Who ran farther, Max or Molly? ________________
2. Who ran faster? ________________ Explain: ____________________________________
_________________________________________________________________________
Gizmo Warm-up
The Distance-Time Graphs GizmoTM shows a graph and a runner on a track. You can control the motion of the runner by manipulating the graph (drag the red dots).
Check that Number of points is 2, and that under Runner 1 both Show graph and Show animation are turned on.
The graph should look like the one shown to the right –
one point at (0, 0) and the other point at (4, 40).
1. Click the green Start button on the stopwatch.
What happens? _______________________________
____________________________________________
2. Click the red Reset button on the stopwatch. The vertical green probe on the graph allows you to see a snapshot of the runner at any point in time. Drag it back and forth. As you do, watch the runner and the stopwatch.
Runner position Be sure the
Number of Points is 2.
In the Gizmo, run the “race” many times with a variety of different graphs. (The red points on the graph can be dragged vertically.) Pay attention to what the graph tells you about the runner.
1. If a distance-time graph contains the point (4, 15), what does that tell you about the runner?
(Be specific, and answer in a complete sentence.) _________________________________
_________________________________________________________________________
2. Look at the graph to the right. Notice where the green probe is. If you could see the runner and the stopwatch at this moment, what would you see?
________________________________________________
________________________________________________
________________________________________________
3. Look at the image below, from the Gizmo. What must be true about this runner’s graph?
_________________________________________________________________________
_________________________________________________________________________
4. The point on the graph that lies on the y-axis (vertical axis) is called the y-intercept. What does the y-intercept tell you about the runner?
_________________________________________________________________________
and speed Click the red Reset button on the stopwatch.
Run the Gizmo several times with different types of graphs. (Remember, the red points on the graph can be dragged vertically.) Pay attention to the speed and direction of the runner.
1. Create a graph of a runner that is running forward (from left to right) in the Gizmo. Sketch your graph to the right.
If the runner is moving from left to right in the Gizmo, how does the graph always look?
__________________________________________________
__________________________________________________
2. Click the red Reset button. Create a graph of a runner that is running from right to left. Sketch it to the right.
How does the graph always look if the runner is moving from right to left in the Gizmo?
__________________________________________________
__________________________________________________
3. Change the Number of Points to 5. Create a graph of a runner that runs left-to-right for one second, rests for two seconds, and then continues running in the same direction. Sketch the graph to the right.
How does a graph show a runner at rest? ________________
__________________________________________________
4. In general, how does a distance-time graph show you which direction the runner is moving?
right. Your graph should include (0, 0), (2, 10), and (4, 40).
A. Where does the runner start? ____________________
B. Where will he be after 2 seconds? ________________
C. Where will he be after 4 seconds? ________________
D. In which time interval do you think the runner will be moving most quickly? (Circle your answer below.)
0 to 2 seconds 2 to 4 seconds
6. Click the Start button and watch the animation. What about the runner changed after 2
seconds of running? ________________________________________________________
_________________________________________________________________________
7. Speed is a measure of how fast something is moving. To calculate speed, divide the distance by the time. In the Gizmo, the units of speed are meters per second (m/s).
A. In the first 2 seconds, how far did the runner go? ____________________________
B. In this time interval, how far did the runner go each second? ___________________
C. In this time interval, what was the runner’s speed? ___________________________
8. Now look at the last two seconds represented on the graph.
A. In the last 2 seconds, how far did the runner go? ____________________________
B. In this time interval, how far did the runner go each second? ___________________
C. In this time interval, what was the runner’s speed? ___________________________
Two runners, two
graphs Under animationRunner 2. , turn on Show graph and Show
1. Experiment with the Gizmo to create each of the following results. (You can use any number of points in your graphs.) Each time you find a solution, click the camera ( ) next to the graph. Then paste the image into a blank document. Label all five images.
Runner 1 wins the race. Runner 2 wins the race.
Runner 2 catches up to and passes runner 1.
Runner 2 is going in the opposite direction as runner 1.
Each runner goes at a different speed, but both reach the finish line together.
2. Based on your experiments, answer the following questions.
A. How does the graph show if a runner gets a head start? ______________________
___________________________________________________________________
B. How does the graph show which runner is faster? ___________________________
___________________________________________________________________
C. How does the graph show which runner wins the race? _______________________
___________________________________________________________________
D. How does the graph show a runner going back and forth? _____________________
___________________________________________________________________
E. What does it mean when the two runners’ graphs cross? _____________________
___________________________________________________________________
3. Challenge: For Runner 2, turn off Show graph. Click New to generate a new random graph
that you can’t see for Runner 2. Click Start, and watch her run. Then try to adjust the graph
solutions in the spaces below. Sketch the graph you made to solve the question in the space to the right of each question.
A. A dog is chasing a cat towards a tree. The cat has a 10-meter lead and runs at a speed of 6 10-meters per second. The dog runs at a speed of 8 meters per second. The
tree is 30 meters away from the dog’s starting position.
Which animal will reach the tree first?
_____________________________________________
B. A police officer is chasing a purse-snatcher down a street. The thief starts 9 meters ahead of the officer and can run 20 meters in 4 seconds (5 m/s). The police officer can run 32 meters in 4 seconds (8 m/s). How long will it take the officer to catch the thief?
_____________________________________________
C. In a football game, one team kicks off to the other. At the moment the receiver catches the ball, he is 40 meters from the nearest tackler. The receiver runs left to right at a speed of 10 meters per second (10 m/s). The tackler runs right to left at a speed of 6 meters per second.
How long does it take before they collide? ___________
How far does the receiver go? _____________________
D. A tortoise challenges a hare to a four-hour race. The hare is so confident of winning that he allows the tortoise to start with a 10-km lead. The hare runs at a speed of 14 km per hour, but stops for a two-hour nap in the middle of the race. The tortoise plods along at 4 km per hour the whole race. Who gets farther in four hours?
_____________________________________________
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Uniform motion can be described with position–time and velocity–time graphs. For example, a UMD car travels across a table at 14.0 cm/s for a total of 7.0 s.
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5
1
3
Video Lab - Graphing Acceleration (p.196)
d
t
v
9 Homework:
Example 1: A baseball leaves a bat and travels straight up into the air,
reaching its highest point 15.9m above the bat in just 1.8s. Determine the
initial velocity of the ball.
Example 2: During a volleyball tournament, a player dives to prevent the
ball from hitting the floor. The ball leaves the player’s outstretched arms
with an initial velocity of 14.5 m/s, and travels straight up stopping 10.7m
above her arms. Calculate the time required for the ball to reach this
displacement.
Example 3: A diver steps off the edge of a platform and enters the water
5.0m below. Determine the time it took for the diver to reach the water.
Summary of Uniform Acceleration:
Equations
Variables
Vi
Vf
a
d
t
Practice:
1. An object that is initially traveling at a velocity of 7.0 m/s east
accelerates uniformly to a velocity of 22.00 m/s in a time of 1.7s.
Calculate the acceleration of the object.
4. Juanita leaves the surface of a trampoline with an initial velocity of
11.8 m/s. Determine her displacement after 0.80s.
5. An object accelerates uniformly from rest. If it travels 26.0 m south
and reaches a velocity of 11.0 m/s south, how long was the object
accelerating?
6. A ball is dropped (not thrown) 10.6 m from the leaning tower of Pisa.
How long does it fall for?
7. A car is traveling 9.5 m/s and accelerates to 13.5 m/s in 6.0 s. How far
does it travel in this time period?
Key Points
• Kinematics describes __________ an object moves (i.e., displacement, velocity, acceleration), while dynamics deals with __________ it moves (i.e., effects of forces).
• Force is a __________ quantity measuring a __________ or __________ on an object. It can have
different magnitudes and can be in different directions.
• In general, any force acting on an object can change the ________________ of an object. • The symbol for force is
F
, and the SI unit for force is the __________ ( ), named after Isaac_________________ (1642-1727).
• One newton is the force required to move a __________ object with an acceleration of __________. That is, 1 newton = 1 ____________.
• An unbalanced force is the __________ of all forces acting on the object. It is also called the ______ force,
F
net.• Newton’s second law of motion states: “When an unbalanced (net) force acts on an object, the object accelerates in the direction of the net force.
• Mathematically, this can be represented as
m
F
a
=
net , wherem
is the mass (in kg).• Newton’s second law is usually written
F
net=
maPractice Problems
1. Suzie takes her 1.5-kg cat for a walk. She exerts a constant force of 30 N on the cat. If the force of friction is 10 N, then what is the cat’s acceleration?
2. A net force of 9.0 N [east] is used to push a 20.0 kg object. What is the acceleration of the object? • Newton’s first law of motion states: “An object will continue either being __________________ or
4. A net force of 10.2 N [east] acts on an object and causes it to accelerate at 0.850 m/s2 [east]. What is the mass of the object?
5. A 16.0-kg object is accelerated at a rate of 2.0 m/s2 by a net force. What is the magnitude of the net force?
