An Introduction to Forces
Definition: A force is a push or a
pull in a particular direction.
How does it balance?
Textbook p. 53
 You probably would be uneasy
standing under Balanced Rock
near Buhl, Idaho. Yet this unusual
rock stays in place year after
year. The rock has forces acting
on it. So, why doesn’t it fall over?
 Answer: The forces acting on the
rock combine, and the rock does
not move.
Now, let’s read page 54.
Remember… A force is a push or
pull in a particular direction.
Forces Packet p. 1
EXAMPLE of a PUSH:
When you ride a bike, your foot
pushes against the pedal. The
push makes the wheels of the
bike move.
EXAMPLE of a PULL:
When you drop something, it is
pulled to the ground by gravity.
Push or Pull
 Push
 Push
 Pull (gravity)
 Push
 Push & Pull
Remember
…
Textbook p. 54, Review from Ch. 2- Lesson 1
There are contact forces.
 Example: Air Resistance, pushing a shopping cart,
pulling on a rope in Tug’o’War
There are non-contact forces.
 Example: Gravity, magnetism, static electricity
The Big Ideas…
Forces Packet p. 1
 Forces can make objects:
start moving.
move faster.
move slower.
stop moving.
change direction.
change an objects shape.
REMEMBER…
Forces Packet p. 1
 Velocity is the speed and direction of a
moving object.
 Acceleration is the measure of the
change in velocity during a period of
time.
 FORCES CAUSE ACCELERATION!
Force Facts…
Forces Packet p. 1
Forces are measured in Newtons (N)
A Newton is equal to the amount of
force required to accelerate a mass of
one kilogram at a rate of one meter per
second
Forces come in pairs.
Forces act in a particular direction.
Forces usually cannot be seen, but
their effects can be seen.
For the next few slides:
Label each picture as
a push or pull.
Forces Packet p. 2
Combining Forces
Textbook p. 55-56, Forces Packet p. 3
Net Force: The combination of all
the forces acting on a object.
 Forces may work together.
This means the forces act in the same direction.
 Forces may be opposite forces.
This means the forces act in opposite directions.
Balanced and Unbalanced Forces
Textbook p. 56, Forces Packet p. 3
Balanced Forces:
Balanced forces
do not cause a
change in
motion.
net force of zero.
 Unbalanced Forces:
 Unbalanced forces
cause a change in
motion.
 net force that
is not zero.
Balanced Forces
Unbalanced Forces
Circle the best answer.
1. The forces above are showing PUSHING/PULLING forces.
2. The forces 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 1000N TO THE LEFT, 1000 N TO THE RIGHT, or
ZERO.
6. There IS/IS NO motion.
Forces Packet p. 4
Answers:
1. The forces above are showing PUSHING/PULLING forces.
2. The forces 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 1000N TO THE LEFT, 1000 N TO THE RIGHT, or
ZERO.
6. There IS/IS NO motion.
Forces Packet p. 4
Circle the best answer.
7. The forces shown above are PUSHING/PULLING forces.
8. The forces shown above are WORKING TOGETHER/OPPOSITE
forces.
9. The forces are EQUAL/NOT EQUAL.
10. The forces DO/DO NOT balance each other.
11. The stronger force is pulling to the RIGHT/LEFT.
12. The weaker force is pulling to the RIGHT/LEFT.
13. The motion is to the RIGHT/LEFT.
Forces Packet p. 5
Answers:
7. The forces shown above are PUSHING/PULLING forces.
8. The forces shown above are WORKING TOGETHER/OPPOSITE
forces.
9. The forces are EQUAL/ NOT EQUAL.
10. The forces DO/ DO NOT balance each other.
11. The stronger force is pulling to theRIGHT / LEFT.
12. The weaker force is pulling to the RIGHT / LEFT.
13. The motion is to the RIGHT/LEFT.
Forces Packet p. 5