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Motion and Forces
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Students are expected to use this as a resource and complete all assignments in a
timely manner as laid out by teacher.
When appropriate labs will be completed.
Motion

Velocity

Acceleration

Motion Graphs
SPS8. Students will determine relationships among force, mass, and motion.
a. Calculate velocity and acceleration.
Essential Question:
How do we use position, velocity, and acceleration to describe the motion of an object?
Assessment:

Calculate velocity of an object, given the displacement and time of measurement
for that object

Calculate acceleration of an object, given the change in velocity and time for that
object

Interpret Motion Graphs.
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Motion
How can you tell if an object has moved?
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
When we describe motion, we use and object’s position and time.
Position
 Distance:
________________________________________________________
o The distance around the track is 440 meters.
o SI unit for measuring distance is meter (m) or meters
 Displacement: Describes how far an object has moved from
___________________________________________________________
o A vector is a quality that has magnitude (number) and direction
o If you run 25 meters straight, your displacement is 25 meters
o If you walk to your friend’s house and later walk back home, the
displacement is 0.
o If your displacement is 0, your velocity is 0.
o If a car travels one mile east and then returns one mile west, to the same
position, the total displacement is zero and so is the average velocity over
this time period.
Speed
 How fast an object moves
 Speed = Distance / Time
 SI units: meters/second, kilometers/hour
 Regular units: miles/hour
 A car travels 750 meters in 25 seconds. What is the cars average speed?
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Velocity
 The speed of an object plus the direction it is moving. (5 m/s North)
 Velocity = displacement / time

SI units: meters/second, kilometers/hour
 Regular units: miles/hour
 Directions: up, down, north, south, east, west, to Georgia, top of mountain, etc.
Sample Problems:
1. Calculate the velocity of a car that travels 556 kilometers northeast in 3.4 hours.
Leave your answer in kilometers per hour.
2. Calculate the velocity, a ball rolling down a 3.4 meter hill in six seconds?
3. A Tom and his family travel 240 miles to the mountains. They spend 3 days, then
return home.
A) What is the total distance Tom’s family traveled?
B) What is the displacement?
Acceleration (m/s2)
 Speed up, slow down, change directions
 Like velocity, has magnitude and direction.
 Acceleration = change in velocity / change in time
 SI units: m/s2
Sample Problems:
1. A car travels from rest to 65 m/s in 10 seconds, what is its acceleration?
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2. A cyclist accelerates from 0 m/s to 8 m/s in 3 seconds. What is his acceleration?
3. A car advertisement states that a certain car can accelerate from rest to 70 km/h
in 7 seconds. Find the car’s average acceleration
4. A lizard accelerates from 2 m/s to 10 m/s in 4 seconds. What is the lizard’s
average acceleration?
5. A train traveling 80 m/s slows down to a stop as it reaches the station. What is
the train’s acceleration?
6. Does a merry-go-round at the fair accelerate? Explain.
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Motion Graphs: Distance / Time and Velocity (speed) / Time
Distance /Time graph
Velocity (speed) /Time Graph
No movement
Constant
movement
Acceleration
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Displacement
-time Graphs
Journey of a Sports Car
A bicycler moves as follows:
Usatestprep.com Assignment: Motion
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Forces
SPS8. Students will determine relationships among force, mass, and motion.
b. Apply Newton’s three laws to everyday situations by explaining the following:

Inertia

Relationship between force, mass and acceleration

Equal and opposite forces
c. Relate falling objects to gravitational force
d. Explain the difference in mass and weight.
Essential Question:
How do forces affect the motion of an object?
Assessment:

Measure and analyze the effects of balanced and unbalanced forces on an object
in motion

Define inertia and recognize common examples of inertia

Recognize the relationship between force mass and acceleration, as described in
Newton’s second law

Calculate the force of an object, given the mass and the acceleration of that
object

Recognize and determine the outcome of common examples of Newton’s third
law

Identify common forces, including friction

Relate falling objects to gravitational force

Contrast mass and weight
Force
A force is a push or a pull
The net force is determined by adding the forces together.
If the forces are pulling in opposite directions with the same strength, the forces will
cancel each other out. If the forces cancel each other out. There is no net force.
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Balanced and Unbalanced Forces
If the net force = 0, the force is balanced.
If the net force NOT = 0, the force is unbalanced
Examples:
Look at the examples
To find the net force, add the opposite forces or the forces moving in the
same direction together.
Picture A:
5 N to the right

Net Force =
15 N
Picture B:
3 N to the left
4 N to the right
- 3 N to the left
2 N to the right
Net Force= 1 N to the right
20 N
What is the net force? ____________
What direction will the object move?
________________________
Is the force balanced or unbalanced?
________________________
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5N
What is the net force? ____________
5N
What direction will the object move? ________
Is the force balanced or unbalanced? _________
2. What is the net force of diagram a.? ______________ Balanced or Unbalanced?
3. What is the net force for diagram b.? ______________ Balanced or Unbalanced?
4. What is the net force of diagram c.? ______________ Balanced or Unbalanced?
5. What is the net force of diagram d.? ______________ Balanced or Unbalanced?
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Friction
Friction is a force that always acts in a direction opposite to the direction of motion.
The amount of friction depends on two things:
1.) The kind of surface the objects have – how smooth or rough
2.) The force that is pressing the objects together – the harder they are pressed
together the more friction there will be
Type of
Friction
Description
Picture
Sliding
Static
Rolling
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Air resistance:
Fluid
Friction
Ways to decrease friction:

We put oil in our cars to reduce friction in the engine. Parts can easily move
against each other with oil. This prevents heat buildup and wearing down parts.

Ball bearings are used to overcome rolling friction.

Aerodynamic designs are used to overcome fluid friction such as air resistance.
Reasons to increase friction:

Provide traction on slippery surfaces: increase roughness

Slow objects down: increase surface area

Generate heat: increase speed
Practice Questions.
1. You push on a crate with a force of 10 N to the right, and your friend pushes on the
crate with a force of 25 N to the left. Describe and explain the motion of the crate.
Draw a picture.
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2. Why do warehouse workers move heavy boxes around on carts with wheels?
3. You push a heavy crate. At first it doesn't move. You push harder, and it finally starts
to move, but you still have to exert some force to keep it moving at a constant velocity.
Explain using the different types of friction.
4. Two crates, one heavy and one light, are at rest on a waxed floor. Which crate will
need the greater force to give the same change in speed? Explain.
5. A boy on a skateboard is pushed down the sidewalk by a friend. The skateboard rolls
for a while but eventually comes to a stop. What force is causing the skateboard to stop
rolling?
6. Explain what the net force on an object will be if balanced forces are acting on it.
What will happen to the net force if unbalanced forces are acting on an object?
7. A large, semi-truck hauling a full load and a small car are traveling in the same
direction. As they approach a sharp curve in the road, which will have a harder time
changing direction and why?
8. A 10.0 kg box is on a frictionless surface. Two forces act on the box as shown below.
What is the net force in the diagram above? In which direction will the box move?
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Gravity
EQ: What is gravity and how does it influence objects?
Gravity attracts all objects towards each other.
Two factors that affect gravity:

Size of the objects

Distance between objects
The bigger an object is, and the closer you are to it, the stronger its gravitational pull is.
The moon’s mass is smaller than Earth’s, so Earth has a greater gravitational pull on the
moon than the moon on Earth. This is why the moon is in Earth’s orbit. The moon’s
gravity affects Earth’s tides.
Jupiter has a much greater mass than Earth, so, it has a greater gravitational pull, but
because our moon is so much closer to Earth than it is to Jupiter, the Earth's
gravitational pull exerts a greater force on the moon than Jupiter does. That's why the
moon isn't pulled out of Earth's orbit by the gravity of larger planets or by the sun.
Gravity is measured in Newtons (N).
Gravity determines an object’s weight.
Mass is a measure of the amount of material in an object. Mass does not change
unless material is added or removed.

An object with a mass of 1 kg on earth would have the same mass of 1 kg on
the moon
Weight is a measure of the force of gravity on an object.
 W = ma
weight = mass x 9.8
o Where “a” is the acceleration due to gravity (9.81 m/s2 on Earth).
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Example:
A car's mass is 1,644 kg. The weight can be calculated:
w = (1,644 kg) (9.8 m/s2)
= 1611.2 N
If the acceleration due to gravity on Jupiter is 26 m/s2, what would your weight be on
Jupiter?
All objects fall toward Earth with the same acceleration regardless of their
mass: 9.8 m/s2 .
This is why if there was no air resistance two falling objects would hit the ground at the
exact same time.
Example Questions:
1. A bowling ball with a mass of 5.44 kg and a soccer ball with a mass of 0.43 kg are
dropped from a 15 m platform, where there is no air friction, identify the correct
description of the acceleration of the bowling ball and the force with it when it hits the
ground, with respect to the soccer ball. Do they hit at the same time?
a. The force of the bowling ball is greater, and its acceleration is greater.
b. The force of the bowling ball is greater, and its acceleration is the same.
c. The force of the bowling ball is the same, and its acceleration is greater.
d. The force on the bowling ball is the same, and the acceleration is the same.
2. What is weight?
a. the force of an object due to gravity
b. the mass of an object
c. the acceleration of gravity
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3. James enjoys throwing the baseball up in the air and catching it. What causes the
baseball to go up, reach its peak,
and then come
down?
a. inertia
b. the downward pull of gravity
c. velocity
Newton’s First Law of Motion
Newton’s Laws of Motion – explain how forces cause motion
Newton’s 1st law – An object at rest remains at rest unless acted on by a force. An
object in_________________ will stay in motion unless stopped by a force.
This is called ________________________ – an object’s resistance to change its
motion.
Inertia is a property of_______________________________.
The amount of inertia that an object has depends on its_____________________. The
more mass an object has, the harder it is to change its __________________________.
Newton’s First Law of Motion is also called the _________________________________
Example of inertia: in an automobile crash a person not wearing a seat belt will keep
moving forward at the car’s speed even after the car has stopped.
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Examples of Newton’s First Law
Blood rushes from your head to your feet while quickly stopping when riding on a
descending elevator.
The head of a hammer can be tightened onto the wooden handle by banging the
bottom of the handle against a hard surface. The top will remain in motion when you
stop the handle. It will slam down on the handle.
To dislodge ketchup from the bottom of a ketchup bottle, it is often turned upside down
and thrusted downward at high speeds and then abruptly halted.
Headrests are placed in cars to prevent whiplash injuries during rear-end collisions.
While riding a skateboard (or wagon or bicycle), you fly forward off the board when
hitting a curb or rock or other object that abruptly halts the motion of the skateboard.
Example Questions:
1. The tendency of an object to resist change in its motion (not wanting to change its
motion) is known as
a. mass.
b. inertia.
c. force.
2. You are riding fast on a skateboard when your wheel suddenly gets stuck in a crack
on the sidewalk. Why does your body go flying forward?
a. there is a net force pushing you off your skateboard
b. your inertia keeps you moving forward
c. someone pushed you
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3. A book is sitting on a dashboard of a car that's stopped at a traffic light. As the car
starts to move forward, the book slides off the dashboard. Pick the most correct
explanation.
a. There was grease on the dashboard
b. The object had inertia.
c. A supernatural force took over.
4. An example of a balanced force is
a. a car sliding on ice.
b. a tug-of-war game in which no one wins.
c. a car hitting a telephone pole.
d. a roller coaster going down the first drop.
Newton’s Second Law of Motion
“A net force acting on an object causes the object to ____________________ in the
direction of the force.”
In other words, force and motion are related.
 The rate of acceleration is determined by the size of the ________ and the mass
of the object.
 An object will have greater acceleration if a _____________ force is applied to it.
 An object with less mass will accelerate faster.
An example of Newton’s Second Law of Motion:
A baseball and a bowling ball are both hit with the same bat and the same force. The
baseball will have a greater acceleration because it has less mass.
All of this is represented mathematically in the equation: F = ma

Where F = force (N)

m = mass (kg)

a = acceleration (m/s2)
“Newton” (N) is a unit of force. It is equal to 1 kg · m/s2.
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Example Questions:
1. What net force is required to accelerate a car at a rate of 5 m/s2 if the car has a
mass of 2,500 kg?
2. What is the acceleration of a 5 kg mass pushed by a 10 N force?
3. Given a force of 56 N and an acceleration of 7 m/s2, what is the mass?
4. How much force is required to accelerate an 8 kg mass at 5 m/s2?
5. What is the acceleration of a 24 kg mass pushed by a 6 N force?
Newton’s Third Law of Motion
“For every ____________ there is an equal and opposite ___________________.”
When you throw a basketball with a force of 3 newtons, the basketball exerts an equal
force back on you.
Example Questions:
1. Joe the fisherman attempts to leap from his small fishing boat to the dock his boat is
next to, but ends up in the water between his boat and the dock, why?
2. Ryan hits a baseball with an acceleration of 45 m/s2. The mass of the baseball is 0.5
kg. What is the force of the swing?
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3. A 2,000 kg car accelerates at the rate of 2.6 m/s2. How much force is required to
achieve his acceleration?
4. A soccer player kicks a 0.5-kilogram stationary ball with a force of 50 newtons. What
is the force on the player’s foot?
a. 0 N
b. 25 N
c. 50 N
d. 100 N
5. What will happen when the skaters push off of each other? Explain using Newton’s
third law. Draw arrows to show the direction the skaters will move.
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