8.6A Balanced & Unbalanced Forces

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Vers. 08/2020

Balanced &
Unbalanced
Forces

Presented by Kesler Science

© Kesler Science, LLC

Balanced and Unbalanced Forces

Essential Questions:

Reflect on the Essential
Questions before you dive in…

1. If you were quizzed today,
which questions would you know
the answers to already?

2. Which questions would you
need to learn more about to
answer confidently?

1.

What are balanced and
unbalanced forces?

2.

How do unbalanced
forces cause a change
in position, direction,
and speed of an
object?

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Balanced and Unbalanced Forces

Force

• A push or a pull from one object on another. It may or

may not cause movement

• Gravity’s force pulls downward toward Earth’s center;

air resistance pushes against moving objects

• Applied force is when a person or object directly pushes

or pulls another object

• Normal (or supporting) force is the name for force that

holds objects in place against gravity or other forces

Example – Gravity pushes a
book down on a table while the
table pushes up on the book

What is the normal force here?

Multiple Choice

A force is a....

• push

• pull

• both

• neither

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Balanced and Unbalanced Forces
Balanced Forces

•Two forces equal in size
and acting in opposite
directions on an object

•The object stays still or
continues to move at the
same (constant) speed and in the same
direction

Example 1: A soccer
ball sitting on the
ground, not moving –
gravity and the
normal force are
equal and opposite

Provide one more example
of balanced forces:

© Kesler Science, LLC

Vers. 08/2020

Balanced Forces Examples

At
rest

At a constant speed
and same direction

At rest

At a constant

speed and same

direction

At rest

Balanced and Unbalanced Forces

Drag and Drop

Examples of balanced forces include​ ​ ​ ​

Placeholder

​ ​

Placeholder

and ​

Placeholder

a

Drag these tiles and drop them in the correct blank above

a book on a shelf

motorcycle at a constant speed

a man sitting on a bench

skier going down a hill

bowling ball thrown down the lane

Two kids playing catch

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Balanced and Unbalanced Forces

Unbalanced Forces

• Two forces that are unequal in size

and opposite in direction

• Always cause a
change in motion in
one of these areas:

• position
• direction
• speed

Example: the moon
orbiting the earth
because it changes
direction/position

Provide two more examples of
unbalanced forces:

Ex 1:

Ex 2:

Multiple Choice

Unbalanced forces can change all EXCEPT

• position

• speed

• direction

• force

10N

20
N

Moves

Left

The student
exerting the
strongest force will
determine the
direction of
movement

Horse #2
is
stronger

Changing directions

Balanced and Unbalanced Forces

Unbalanced Forces Examples

Drag and Drop

Examples of unbalanced forces include​ ​ ​ ​

Placeholder

​

Placeholder

and ​

Placeholder

Drag these tiles and drop them in the correct blank above

a bowling ball thrown down the lane

two kids playing catch

a skier going down a hill

book on a shelf

man on a bench

motorcycle at a constant speed

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Balanced and Unbalanced Forces

Net Force

•The overall forces acting
on an object

•Measured in Newtons (N)

3N

2N

Net
Force

1N

Which way will the people on the right move? Why?

Multiple Choice

Force is measured in what?

• Newtons

• Neutrons

• Pounds per square inch

  (PSI)

• Net force

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Balanced and Unbalanced Forces

How do unbalanced forces cause a change in
position of an object?

•A skier is at the top of a hill
(balanced force). Another skier
bumps him (unbalanced force)
causing him to fall down

•This unbalanced forced caused
his position to change

In your own words, how does an
unbalanced force cause a change in
position of an object?

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Balanced and Unbalanced Forces

How do unbalanced forces cause a change in
direction of an object?

•A skier is at the top of a hill
(balanced force). Then then the
skier decides to point her skis
down the hill and push off
(unbalanced force)

•This unbalanced force causes her
a change in direction

In your own words, how does an
unbalanced force cause a change in
direction of an object?

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Balanced and Unbalanced Forces

How do unbalanced forces cause a change in
speed of an object?

•A skier is at the top of a hill
(balanced force) at the
beginning of a race. As he flies
down the mountain (unbalanced
force) he picks up speed

•This unbalanced force causes him
a change in speed

In your own words, how does an
unbalanced force cause a change in
speed of an object?

Think About It

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Isaac Newton’s third law of motion states that for
every action, there is an equal and opposite reaction.
That means if a car collides with a brick wall, the
same force pushes back against the car. This is why
cars that drive into brick walls don’t look so good!

If you were about to run into a brick wall, would
hitting your brakes help lessen the force of the
collision? Even if you knew they couldn’t completely
stop you? Why or why not?

Multiple Choice

Based on what you just learned, what direction will this box move and with what amount of force?

• to the left

  43 Newtons of force

• to the right

  43 Newtons of force

• to the left

  7 Newtons of force

• to the right

  7 Newtons of force