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Force - a push or pull on an object
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A force can change the direction of an object.
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Scientists express force using a unit called the
Newton (N). One Newton of force is the
amount needed to accelerate a mass 1kg in size
1.0 m/s/s.
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Forces affect how objects move.
Motion is any physical movement
or change in position or place.
The starting point you use to describe the motion
of an object is called the reference point.
 While using a reference point to describe motion,
you will also need to state the direction of the
movement.
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Direction may be up or down, right or left, north
or south, east or west, etc.
PRACTICE

Describe the force needed to put each
object in motion.
Net Force is the combination of ALL the forces
acting on an object. The Net Force is dependent
upon the direction of the forces.
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Balanced Forces = NO Motion
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The net force = Zero
Unbalanced Forces = MOTION

The net force = SUM of the two
forces

When two unequal forces act in opposite
directions on an object, the net force is the
difference of the two forces. The final force and
its direction are called a resultant.
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Practice
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1. The forces shown above are PUSHING / PULLING
forces.
2. The forces shown above are WORKING
TOGETHER / OPPOSITE FORCES.
3. The forces are EQUAL / NOT EQUAL.
4. The forces DO / DO NOT balance each other.
5. The resultant force is 1000 N TO THE RIGHT / 1000
N TO THE LEFT / ZERO.
6. There IS / IS NO motion.
Answers:
1. The forces shown above are PUSHING /
PULLING forces.
2. The forces shown above are WORKING
TOGETHER / OPPOSITE FORCES.
3. The forces are EQUAL / NOT EQUAL.
4. The forces DO / DO NOT balance each other.
5. The resultant force is 1000 N TO THE RIGHT /
1000 N TO THE LEFT /ZERO.
6. There IS / IS NO motion.
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Practice

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1. The forces shown above are WORKING
TOGETHER / OPPOSITE FORCES.
2. The forces are EQUAL / NOT EQUAL.
3. The forces DO / DO NOT balance each other.
4. The stronger force is pulling to the RIGHT /
LEFT.
5. The weaker force is pulling to the RIGHT /
LEFT.
6. Motion is to the RIGHT / LEFT.
Answers:
1. The forces shown above are WORKING
TOGETHER / OPPOSITE FORCES.
2. The forces are EQUAL / NOT EQUAL.
3. The forces DO / DO NOT balance each other.
4. The stronger force is pulling to the RIGHT /
LEFT.
5. The weaker force is pulling to the RIGHT /
LEFT.
6. Motion is to the RIGHT / LEFT.
Forces Acting on Objects
Depending on the situation, there will be certain forces
acting upon an object.
 Here are a few forces that we will be using for this unit:
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Normal Force: The support force applied to an object that is in
contact with another stable object.
Gravity Force: The force with which the earth, moon, or other
massively large object attracts another object towards itself.
Gravity will always be a force acting on an object.
Air Resistance: A special type of frictional force that acts upon
objects as they travel through the air. The force of air resistance is
often observed to oppose the motion of an object.
Vectors
Despicable Me Clip:
https://www.youtube.com/watch?v=bOIe0
Each square represents 1 N.
DIMbI8
 A vector shows the direction and the
magnitude (amount) of a force.

It is a line with an arrow and begins with a
dot.
 The length of the arrow shows the amount of
force.
 The arrow shows the direction of the force.
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Practice
Force Diagrams

A science book is at rest on a table top. Diagram the forces
acting on the science book.
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A skydiver is descending with a constant velocity.
Consider air resistance. Diagram the forces acting on the
skydiver.
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Two teams are competing in a tug-of-war contest. Team A
is pulling at 4000N and Team B is pulling at 4900N is the
opposite direction. Sketch the forces and show the net
force exerted. Which team is winning? Is this force
balanced or unbalanced?

Tommy and John are trying to move a large table. John
pushes with a force of 1150N and Tommy helps him by
pushing on the same side of the table with a force of 800N.
Sketch the individual forces exerted on the table and then
calculate and show the net force exerted on the table.
A science book is at rest on a
table top. Diagram the forces
acting on the science book.
A skydiver is descending with a
constant velocity. Consider air
resistance. Diagram the forces
acting on the skydiver.
Two teams are competing in a tugof-war contest. Team A is pulling
at 4000N and Team B is pulling at
4900N is the opposite direction.
Sketch the forces and show the
net force exerted. Which team is
winning? Is this force balanced or
unbalanced?
Tommy and John are trying to
move a large table. John pushes
with a force of 1150N and Tommy
helps him by pushing on the same
side of the table with a force of
800N. Sketch the individual
forces exerted on the table and
then calculate and show the net
force exerted on the table.
Calculating Net Force Examples
An object has 2 forces pushing on the left.
One force is 30 N and the other force is 15
N. What is the net force? Is it balanced or
unbalanced? What direction is the object
moving?
 An object has a force of 10 N pushing from
the left and 2 forces (15 N and 5 N)
pushing from the right. What is the net
force? Is it balanced or unbalanced? What
direction is the object moving?
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What do you think the activity
in the beginning of class was
demonstrating?