2. Forces Intro #4 (New Pink) May the Forces be with you.....

3. 1) Force: a push or pull on an object
Has its own unit… The Newton (N)
Anytime you see something moving… a force caused it.
Where is this jeep exerting a force?
What’s keeping it from moving?

4. What are some forces you cannot see?
Write Down 3
Wind
Water
Underwater currents at the beach
Magnets
Gravity
Static cling

5. 2) Forces in combination
The net force is the result of 2 or more
forces acting on a object.
Forces combine in 2 ways

6. Forces in the same direction are added together
Julio was pulling at the front of the car (20N) and Alex was pushing at the back (35N).
What was the net force?
20 N + 35 N = 55 N

7. Forces in Different Directions are subtracted.
Subtract the largest from the smallest
Vader and Snow were in a
rough tug of war for the rope.
Vader was pulling 55 N. Snow was pulling 57 N.
What was the net force?
57 N – 55 N = 2 N

8. Practice Jorge, Tony, and Chris we're all pushing a
couch into the other room.
What is their net force?
Jorge 13 N,
Tony 14N,
Chris 17 N
13N + 14N + 17N = 44N
Sharon and Destiny
were both pushing on
opposite sides of a soda
machine attempting to
rock it.
What is their net force?
Sharon 13N, Destiny 14 N
14N – 13 N = 1 N

9. Unbalanced vs. Balanced Forces
Net force is not zero so there is a change in motion
Ex. Car was pushed and pulled, snow won the tug of war
Can also include a change in direction…
Ex. Kicking a Soccer ball
Balanced
Forces acting on an object that cancel each other out... = no motion!
Ex. Hat resting on your head… what forces are generated?
This also called Equilibrium

10. There are two forces acting upon the book.
Since these two forces are
• equal size (also called magnitude) and
• opposite directions, they balance each other out.
The forces are balanced so the book is not moving
either direction. It is in equilibrium.

11. Again (because it’s important!)
When the forces are balanced, the net force is zero.
When the net force on an object is zero, we say the object is in equilibrium.

12. Equilibrium and normal forces
A normal force is created whenever an object is in contact with a surface.
The normal force is equal to the downward force (weight.)

13. Another example of a balanced force
A person standing
upon the ground is in equilibrium.
(What is the normal force observed here?)

14. Solving equilibrium problems
For an object to be in equilibrium, all the forces acting on the object must add to zero.
Do not mix forces in the horizontal direction with forces in the vertical (up and down) direction.
What is the net force on this block?
Will it move?