What is a Force?
Station 2
When you drop something it is
pulled to the ground by gravity.
When you ride your bike, your foot
pushes against the pedal. The push
makes the wheels of the bike move.
1. What is a Force?
Any push or pull which causes something to
move or change its speed or direction
2. Give an example of a pushing force
and a pulling force at school:
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3. Forces can affect motion in several ways
They can make objects:
• Start moving
• Stop moving
• Slow down
• Speed up
• Change direction
• Change shape
Task: Match up the examples from the
station card with the changes in motion they
represent. Record your answers in your
student packet!
They can make objects:
• Start moving
Push a shopping cart
Skateboarding down a hill
Slam on the brakes
Hit a baseball with a bat
Coast to a stop on a bike
Mold a piece of clay
They can make objects:
• Stop moving
Push a shopping cart
Skateboarding down a hill
Slam on the brakes
Hit a baseball with a bat
Coast to a stop on a bike
Mold a piece of clay
They can make objects:
• Slow down
Push a shopping cart
Skateboarding down a hill
Slam on the brakes
Hit a baseball with a bat
Coast to a stop on a bike
Mold a piece of clay
They can make objects:
• Speed up
Push a shopping cart
Skateboarding down a hill
Slam on the brakes
Hit a baseball with a bat
Coast to a stop on a bike
Mold a piece of clay
They can make objects:
• Change direction
Push a shopping cart
Skateboarding down a hill
Slam on the brakes
Hit a baseball with a bat
Coast to a stop on a bike
Mold a piece of clay
They can make objects:
• Change shape
Push a shopping cart
Skateboarding down a hill
Slam on the brakes
Hit a baseball with a bat
Coast to a stop on a bike
Mold a piece of clay
4. Force Facts
 Forces
are measured in Newtons (N)
 Forces usually act in pairs
 Forces can usually not be seen but their effects
can!
5. How Do Forces Combine?
When all of the forces acting on the object
are added together, you determine the net force.
Solve the following net
force practice problems
in your student packet.
Make sure you show
your work!!
6. Net Force Practice Problems:
Problem A: You and your brother are pushing
a car with a dead battery with forces of 20 N
and 25 N in the same direction. What is the net
force applied on the car?
6. Net Force Practice Problems:
Solution A:
Since you are pushing the car in the same
direction, the forces will be added together.
Net force = 20 N + 25 N
Net force = 45 N
6. Net Force Practice Problems:
Problem B: What is the net force on the
airplane?
6. Net Force Practice Problems:
Solution B:
The airplane is moving with a force of 800 N.
However, there are two forces moving in opposite
directions on the airplane.
6. Net Force Practice Problems:
Solution B:
Just add these two forces: 40 N + 60 N = 100 N
Subtract to get the net force: 800 N - 100 N = 700 N
The net force is 700 N.
The airplane will move with a force of 700 N as a result
of air friction and wind.
6. Net Force Practice Problems:
Problem C:
A brother is pulling a toy from his sister with a
force of 6 N. The sister is pulling back with a
force of 8 N.
Draw a picture showing the situation and
determine the net force.
Who gets the toy?
6. Net Force Practice Problems:
Problem C:
A brother is pulling a toy from his sister with a
force of 6 N. The sister is pulling back with a
force of 8 N.
8N
8N-6N
=2N
Sister!
6N
6. Net Force Practice Problems:
Problem D:
4 people are playing tug of war. Two are pulling
on the right side. Two are pulling on the left
side. On the right side, one is pulling with a
force of 60 N and the other with a force of 70 N.
On the left side, one is pulling with a force of 30
N.
Draw a picture to represent the situation.
6. Net Force Practice Problems:
Problem D:
How much force should the second person on
the left apply to keep the rope in equilibrium?
30 + X
60 + 70
30 + 100
130 N
7. Balanced Forces
All forces acting on an
object are equal in size
and in opposite directions
There is no motion
Net force of zero
8. Unbalanced Forces
All forces acting on an
object are NOT equal in
size
There IS motion
One of the forces is
stronger than the other
9. Balanced or Unbalanced?
Car at a stop sign
9. Balanced or Unbalanced?
Running to first base
9. Balanced or Unbalanced?
Books on the desk
!
9. Balanced or Unbalanced?
Airplane taking off
10. Look at this
picture and give two
examples of a
balanced force and
two examples of an
unbalanced force:
Force
and
Motion