Section 1.1.2 –
“Introduction to
Forces (Unbalanced
& Balanced)”
7.P.1.2 Explain the effects of balanced and unbalanced forces acting on an object (including
friction & gravity).
KAHOOT MINI QUIZ –
“INTRODUCTION TO FORCES!”
Lesson Objectives
By the end of this lesson, students will be able to:
I. Explain that motion is a result of forces acting on an object
- Describe how objects at rest resist a change in their position or direction of motion.
- Describe how objects in motion resist a change in their position.
- Use knowledge of forces and inertia to analyze how an object moves.
- Classify that forces are at work in a given situation such as balanced or unbalanced.
II. Explain that changes in motion are due to unbalanced forces acting on an object
III. Describe Newton’s First Law of Motion
IV. Create examples of real life situations where forces are at work.
V. Briefly describe how changes in velocity, acceleration, and speed affect motion.
Lesson Questions
By the end of this lesson, students will be able to answer:
I. What kinds of forces can act on an object?
II. What happens when two unbalanced forces act on an
object?
III. Why does an object change its position when there is
unbalanced force acting on it?
What Kinds of Forces Act
on an Object?
There are many different kinds of forces.
I.
Contact forces: are forces that occur when two masses are
directly touching, such as the force of friction.
II. Frictional forces: oppose motion, and are dependent on the
nature of the materials in contact, the mass of the
materials in contact, and other forces acting on the
materials in contact.
III. Forces that can act from a distance are the electrical force,
magnetic force, and gravitational force. Forces that can act
from a distance tend to be stronger as the distance
between interacting objects decreases.
What Kinds of Forces Act
on an Object?
• On Earth’s surface, the forces of gravity
and friction act on all moving objects, so
moving objects do not stay in motion for
very long.
• Gravity pulls objects downward.
• Friction acts against the direction of
movement.
• For example, when you throw a ball on
Earth’s surface the ball falls back to Earth
and stops rolling on the ground due to
the unbalanced forces of gravity and
friction. However, if you threw a ball in
space it would continue to move in a
straight line until an unbalanced force
acted on the object to change its motion.
I think Bernie wants to play
“fetch”. What types of forces
allow bernie to play fetch on
Earth? How is Bernie able to run
after the ball?
What Kinds of Forces Act
on an Object?
Frictional Force
Gravitational Force
What happens when two unbalanced
forces act on an object?
• A force is a push or a pull.
How do you suppose a vector diagram
should look according to the car?
• When a force is applied to one object by a Include Friction, Gravity, and the
second object, the first object will exert an “Motor” of the car.
equal and opposite force on the second
object. If there is only one force acting on
an object, that object will move in the
direction of the applied force.
• If there are multiple forces acting on an
object from different directions, the net
movement of the object will be in the
direction indicated by the sum of the
vectors corresponding to each force.
• Note that this net movement will not be in
the direction of the strongest force.
Why does an object change its position when
there is unbalanced force acting on it?
• A force is a push or a pull
• Objects move due to forces that act on
an object.
• When all the forces acting on an object
are balanced, the object’s motion does
not change.
• This phenomenon is described by
Newton’s First Law of Motion, which
states that an object at rest will stay at
rest and an object in motion will
continue moving in a straight line unless
an unbalanced force acts on the object.
• This tendency to resist a change in
motion is called inertia. It takes an
unbalanced force to overcome inertia
and change an object’s motion.
Does the coin have inertia?
Explain your reasoning?
Common Misconceptions
• Students may believe that force is a property that an object
has, and when it stops moving, it has run out of force. In fact,
a force is an interaction between two objects.
• Students may believe that a force must be constantly applied
to an object for that object to stay in motion. In fact,
according to the law of inertia an object in motion will stay
in motion unless acted on by an unbalanced force. This
means that, barring other outside forces, an object that is
moving does not require the constant application of a force
in the direction of motion.
Check for Understanding:
StudyJams – Forces & Motion
• Complete the studyjams activity – Forces & Motion
• View the video, and take notes on a pages document (you may
keep the pages document for future reference)
• Download the pages document labeled “StudyJams – Forces &
Motion Mini-Quiz” on the class weebly website!
Small Group Instructional
Activities
I. Exploration: “Monster
Truck Pull”
II. Reading Exploration:
“Look Out Below”
Make sure you download the pages document on the class website link!
Section 1.1.2 Review
I. What kinds of forces can act on an object?
II. What happens when two unbalanced forces act on an
object?
III. Why does an object change its position when there is
unbalanced force acting on it?
That was a lot for one day!
Let’s take a break!!!